[Federal Register Volume 72, Number 22 (Friday, February 2, 2007)]
[Proposed Rules]
[Pages 4967-4997]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 07-429]
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DEPARTMENT OF THE INTERIOR
Fish and Wildlife Service
50 CFR Part 17
Endangered and Threatened Wildlife and Plants; 12-Month Finding
on a Petition To List the American Eel as Threatened or Endangered
AGENCY: Fish and Wildlife Service, Interior.
ACTION: Notice of 12-month petition finding.
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SUMMARY: We, the U.S. Fish and Wildlife Service (USFWS), announce our
12-month finding on a petition to list, under the Endangered Species
Act of 1973, (Act) as amended, the American eel (Anguilla rostrata) as
a threatened or endangered species throughout its range. After a
thorough review of all available scientific and commercial information,
we find that listing the American eel as either threatened or
endangered is not warranted at this time. We ask the public to continue
to submit to us any new information that becomes available concerning
the status of or threats to the species. This information will help us
to monitor and encourage the ongoing conservation of this species.
DATES: The finding in this document was made on February 2, 2007.
ADDRESSES: Data, information, comments, or questions regarding this
finding should be sent by postal mail to Martin Miller, Chief, Division
of Endangered Species, Region 5, U.S. Fish and Wildlife Service, 300
Westgate Center Drive, Hadley, Massachusetts 01035-9589; by facsimile
to 413-253-8428; or by electronic mail to [email protected].
FOR FURTHER INFORMATION CONTACT: Heather Bell, at the street address
listed in ADDRESSES (telephone 413-253-8645; facsimile 413-253-8428).
Persons who use a telecommunications device for the deaf (TDD) may call
the Federal Information Relay Service (FIRS) at 800-877-8339, 24 hours
a day, 7 days a week.
SUPPLEMENTARY INFORMATION: The complete administrative file for this
finding is available for inspection, by appointment and during normal
business hours, at the street address listed in ADDRESSES. The petition
finding, the status review for American eel, related Federal Register
notices, and other pertinent information, may be obtained online at
http://www.fws.gov/northeast/ameel/.
Background
Section 4(b)(3)(B) of the Act, as amended (16 U.S.C. 1531 et seq.),
requires that, for any petition to revise the Lists of Endangered and
Threatened Wildlife and Plants that contains substantial scientific and
commercial information that listing may be warranted, we conduct a
status review and make a finding within 12 months of the date of
receipt of the petition (hereafter referred to as a 12-month finding)
on whether the petitioned action is (a) not warranted, (b) warranted,
or (c) warranted but the immediate proposal of a regulation
implementing the petitioned action is precluded by other pending
proposals to determine whether any species is threatened or endangered,
and expeditious progress is being made to add or remove qualified
species from the Lists of Endangered and Threatened Wildlife and
Plants.
On May 27, 2004, the Atlantic States Marine Fisheries Commission
(ASMFC), concerned about extreme declines in the Saint Lawrence River/
Lake Ontario (SLR/LO) portion of the species' range, requested that the
USFWS and the National Oceanic and Atmospheric Administration's
National Marine Fisheries Service (NMFS) conduct a status review of the
American eel. The ASMFC also requested an evaluation of the
appropriateness of a Distinct Population Segment (DPS) listing under
the Act for the SLR/LO and Lake Champlain/Richelieu River portion of
the American eel population, as well as an evaluation of the entire
Atlantic coast American eel population (see Finding for definition of
DPS) (ASMFC 2004a, p. 1). The USFWS responded to this request on
September 24, 2004; our response stated that we had conducted a
preliminary review regarding the potential DPS as described by the
ASMFC, and determined that the American eel was not likely to meet the
discreteness element of the policy requirements due to lack of
population subdivision (further analysis is provided under Finding).
Rather, the USFWS agreed to conduct a rangewide status review of the
American eel in coordination with NMFS and ASMFC (USFWS 2004, p. 1).
On November 18, 2004, the USFWS and the NMFS received a petition,
dated November 12, 2004, from Timothy A. Watts and Douglas H. Watts,
requesting that the USFWS and NMFS list the American eel as an
endangered species under the Act. The petitioners cited destruction and
modification of habitat, overutilization, inadequacy of existing
regulatory mechanisms, and other
[[Page 4968]]
natural and man-made factors (such as contaminants and hydroelectric
turbines) as the threats to the species.
On July 6, 2005, in response to the petition, the USFWS issued a
90-day finding on the petition (70 FR 38849), which found that the
petition presented substantial information indicating that listing the
American eel may be warranted. The finding noted concern that the
dramatic decrease in recruitment of American eel noted at the Moses-
Saunders Dam in Canada (on the St. Lawrence River), coupled with the
significant decline seen in the European eel (ASMFC 2000, pp. 12-14),
could indicate a decline in the American eel. Information on possible
reasons for this suggested decline included the following threats:
Commercial harvest, habitat loss and degradation (primarily the loss of
wetlands and upper tributary habitat), hydropower turbine mortality,
and inadequacy of existing regulatory mechanisms. Other potential
threats, such as seaweed harvest, benthic (sea or lake bottom) habitat
destruction, alterations of stream flow, disease, predation, and
contaminants, were not fully addressed or supported by the information
presented in the petition. Further analysis of oceanic variations (such
as changes in the Gulf Stream) were recommended in the 90-day finding,
particularly in light of the scant direct evidence and the potential
for oceanic variations to be compounding or confounding the impact of
other threats. Additionally, the 90-day finding concluded that the
complex life history and the incompleteness of historical data
(abundance, stock composition, life stage mortality rates, and
exploitation rates) made it challenging to understand the potential
influence of multiple threats to the American eel (USFWS 2005a, p.
38860).
In response to our 90-day finding's request for information for use
in the species' status review, we received comments and information on
American eel from the majority of the State fish and wildlife agencies
within the range of the eel; State universities; State and university
museums; the U.S. Forest Service (USFS); National Park Service (NPS);
U.S. Geological Survey (USGS); Army Corp of Engineers (ACOE); the
Department of Defense; the ASMFC; the Great Lakes Fisheries Commission;
Department of Fisheries and Oceans (Canada); Tribal Nations; academics
and researchers from the United States, Canada, Japan, and several
European countries; hydropower and fishing industries; nongovernmental
organizations; private citizens; and other entities. Additionally, we
coordinated with the USFWS's International Affairs Program (IAP) to
obtain information on international trade and with State and Federal
law enforcement officials on illegal trade. Although all countries
where the American eel is native were contacted regarding information,
there was no available data on eel distribution, habitat use, habitat
degradation or loss, or other threats (other than international harvest
data) from Central or South America. Distribution information was
provided by some Caribbean Islands. Therefore, the status review
focused on where data is available within the North American Continent.
A status review allows for additional collection, clarification,
and interpretation of information on the status of the species by the
USFWS. The resulting status review, from which the 12-month finding is
based, relied on our extensive review of the existing literature, data
resulting from the 90-day finding request for information, and new
information obtained during the status review period. Among the new
information we received, the documents most relevant to the status
review include the recently completed stock assessments for the
Atlantic coast (ASMFC 2006a and b), the American eel data assembled for
the Canadian stock assessment (Cairns et al. 2005), and recently
completed research on life history and potential threats to the
American eel (van den Thillart et al. 2005; Oliviera in USFWS 2006;
Machut 2006; Lamson et al. 2006; Devarut et al. 2006; Knights et al.
2006).
Also, because of the large body of literature and the uncertainty
surrounding several threats, we hosted two scientific workshops with
over 25 scientific experts. The goal of the workshops was to insure
that the USFWS properly utilized the best and most current scientific
and commercial data available in conducting the status review. To reach
this goal, each of the experts was asked a series of facilitated
questions to assess the presented information (which included multiple
factual inputs, data, models, assumptions, etc.), including the
completeness of the literature selected, and to comment on the
relevance and quality of the literature for purposes of our status
review (see workshop summaries Web site at http://www.fws.gov/northeast/ameel/). The USFWS recorded each expert's individual
assessments and the basis for those assessments in a compendium (cited
in the finding as USFWS 2005b and 2006). Workshop objectives included
determining the following: Utility of the information; life history
stages vulnerable to certain threats; the geographic scope of the
threats; the immediacy of the threats; and uncertainties in the
available information and the potential implications of those
uncertainties in making a status determination.
The selection of the expert panelists was based on recommendations
from within and outside of the USFWS and NMFS (the Services). The
panelists selected represented a broad and diverse range of scientific
perspectives relevant to the status review of the American eel coming
from State and Federal agencies, fishery commissions, Tribes, academia,
domestic and foreign research institutions (Canada, Japan, and
England), industry organizations, and nongovernmental organizations.
Participating individuals had expertise on threats or life history
characteristics associated with threats to the American eel.
Therefore, in addition to the published literature, our review
considered: (1) Each expert panelist's characterization of the threat
(the life stages acted upon by the threat, the severity of the threat,
and the timing of the threat) based on their own and other published
and unpublished research on the species; (2) the basis for each expert
panelist's assessments of the literature in the context of a rangewide
status review; and, (3) each expert panelist's assessments of the
implications of the uncertainty in the information. This finding
therefore builds on, clarifies, reinterprets, and, in some cases,
supersedes information presented in the 90-day finding.
In conducting our 12-month finding for American eel, we considered
all scientific and commercial information on the status of American eel
that we had in our files. Parallels in life history traits that are
unknown for the American eel are drawn from other species of Anguilla.
Evolution and Population Structure
The American eel is one of 15 ancient species (evolving circa 52
million years ago) of the worldwide genus Anguilla, whose members spawn
in ocean waters, migrate to coastal and inland continental waters to
grow, and then return to ocean spawning areas to reproduce and die--a
life history strategy known as catadromy (McCleave 2001a, p. 800; Avise
2003, p. 31; Knights et al. 2006, pp. 2-3).
The North Atlantic is home to two, closely related, recognized
species of Anguilla--the American eel and the European eel (A.
anguilla) (Avise 2003, p. 31). Genetic research indicates that the
American eel lacks appreciable phylogeographic population structure,
[[Page 4969]]
meaning that American eels are one, well-mixed, single breeding
population, termed panmixia or panmictic (Avise 2003, pp. 34-35). This
likely occurs from a combination of the random distribution of the
eel's larval stage when they reach continental waters and random mating
among all adults throughout the species' range. This is in contrast to
many anadromous species (which, even though they have an oceanic phase,
return to their rivers of origin to spawn), where mating is within
separate populations that are geographically or temporally isolated.
This panmictic life history strategy maximizes adaptability to
changing environments and is well suited to species that have
unpredictable larval dispersal to many habitats (Stearns 1977 in
Helfman et al. 1987, p. 52). Additionally, by not exhibiting geographic
or habitat-specific adaptations, eels have the ability to rapidly
colonize new habitats and to re-colonize disturbed ones over wide
geographical ranges (McDowall 1996 in Knights et al. 2006, p. 7).
Life History
In brief, the life history of the American eel begins in the
Sargasso Sea, where eggs hatch into a larval stage known as
``leptocephali.'' These leptocephali are transported by ocean currents
to the Atlantic coasts of North America and upper portions of South
America. They enter coastal waters, where they may stay, or they may
move into estuarine waters or migrate up freshwater rivers, where they
grow as juveniles and mature. Upon nearing sexual maturity, these eels
begin migration toward the Sargasso Sea, completing sexual maturation
en route. Spawning occurs in the Sargasso Sea. After spawning, the
adults die; a species with this life history trait is known as a
semelparous species. For a detailed description of the life cycle and
other life history characteristics, see McCleave 2001a, Tesch 2003, and
Cairns et al. 2005. Aspects of the species' life history most relevant
to this finding are discussed in more detail below.
Egg and Larval Life History Stage
The egg and larval stage of the American eel occur in the Atlantic
Ocean, the Sargasso Sea, ocean currents, and Continental Shelf waters.
Sargasso Sea. The Sargasso Sea is part of the North Atlantic Ocean,
lying roughly between the West Indies and the Azores. The Sargasso Sea
is part of the western half of a large clockwise gyre (circular pattern
of ocean circulation). It is here that American eel eggs hatch into a
larval stage known as ``leptocephali.'' The leptocephali are
distributed in the upper 300 meters (m) of the ocean and are subject to
transport from surface currents in the Sargasso Sea. These surface
currents can be complex due to the fronts that form in the Subtropical
Convergence Zone (where equatorial and temperate waters meet) primarily
in the winter and spring, and the eddies that are likely present year
round.
Ocean current transport. The Sargasso Sea includes a powerful
western boundary current, the Florida Current and Gulf Stream, which
flows to the north and northeast along the Atlantic coast of North
America. The Florida Current is the southern half of this flow, from
the Straits of Florida to Cape Hatteras (Schott et al. 1988 in Miller
2005, p. 3). The Florida Current transports water from the Caribbean,
Gulf of Mexico, and more distant regions through the Straits of
Florida. It then combines with Gulf Stream recirculation water from the
Sargasso Sea as it flows north of the Bahamas (Marchese 1999, pp. 29,
549), and forms the Gulf Stream off Cape Hatteras, North Carolina. Once
past Cape Hatteras, the Gulf Stream (which is at least 48 km or 30
miles offshore but more typically 160 km or 100 miles or greater
offshore) usually has pronounced meanders, which, if large enough, can
get separated and cast off to the north into the continental slope
water (a water mass found in the permanent thermocline between the Gulf
Stream and the continental shelf north of Cape Hatteras (35 [deg]N)).
The flow of the Gulf Stream continues to the northeast, mostly
paralleling the Atlantic coast, towards Europe and becomes the North
Atlantic Current (Miller 2005, pp. 3-4).
The majority of the leptocephali enter the Florida Current just
south of Cape Hatteras (just south of where the Florida Current enters
the Gulf Stream) directly from the Sargasso Sea. The remainder may
enter the Florida Current by a more southern route (e.g., transported
on the Caribbean Current through the Yucatan Straights (Kleckner and
McCleave 1985, p. 89), to the Gulf Loop Current and then to the Florida
Current, which would be the route most likely taken for Gulf of Mexico
recruitment) (Kleckner and McCleave 1982, p. 329-330; Miller 2005, p.
3).
The distribution of American eel leptocephali in the Florida
Current was first described by Kleckner and McCleave (1982, pp. 334-
337; 1985, pp. 73-77). Additionally, they found evidence of westward
movement of leptocephali across the current toward the coastal waters.
Because the distances of transport, to southern and northern points
along the Atlantic coast, differ by thousands of kilometers, it has
been suggested that the timing of metamorphosis from leptocephali to
the next life history stage may determine where individuals arrive in
Continental Shelf waters.
Other than likely current transport, we know very little about the
American eel leptocephali. Recent studies on other species have
indicated that leptocephali may feed on marine snow or specific
detrital particles, such as discarded larvacean (planktonic tunicates
that secrete a gelatinous house) houses and zooplankton fecal pellets
(Otake et al. 1993, pp. 28-32; Mochioka and Iwamizu 1996, p. 447).
Continental shelf waters. The American eel undergoes metamorphosis
twice. The first occurs when the leptocephali enter the Continental
Shelf waters (the area of shallow seas just off the coast to the area
of marked increase in slope to greater depths); the second is during
sexual maturation. The leptocephalis' leaf-like, laterally compressed
shape transforms during metamorphosis into a reduced,
characteristically eel-like shape, as they become transparent ``glass''
eels. Leptocephali are unusual fish larvae that are filled with a
transparent gelatinous energy storage material, and they can swim
either forwards or backwards (Miller and Tsukamoto 2004 in Miller 2005,
pp. 1-2); this may be an important aspect in detraining from (getting
off of) the Gulf Stream. According to Miller (2005), this directional
swimming appears to be the only way that leptocephali can cross and
detrain from the Gulf Stream system and cross the Continental Shelf
waters, due to the lack of any persistent oceanic transport mechanism
that can account for the large-scale transport of millions of larvae
across the current.
Juvenile Life History Stage
Arrival in coastal waters. When juvenile eels arrive in coastal
waters, they can arrive in great density and with considerable yearly
variation (ICES 2001, p. 2). Arriving juvenile eels (unpigmented
``glass eels'' and pigmented ``elvers'') have been collected and
recorded for 10 years from two sites in North Carolina in the Beaufort
estuary. Densities as high as 13.5-14.0 eels/100m\3\ and as low as 1.5
eels/100m\3\ have been recorded (Powles and Warlen 2002, p. 301). In
the East River, Canada, Jessop (2000, p. 520) had daily counts of
30,000 elvers entering the mouth of the river. Between May and August
200,000 elvers were recorded by trap method, and a population estimate
of 960,000 elvers was conducted by mark-
[[Page 4970]]
recapture (Jessop 2000, pp. 518-520). Variation in recruitment between
years can be quite significant. In the 9 years of records between the
years 1982 to 1999, estimated recruitment to the Petite rivi[egrave]re
del la Trinit[eacute] varied roughly four-fold, from a low of 14,014 to
a high of 61,308 (ICES 2001, p. 36). Some arrivals remain in brackish
(estuarine) or marine (salt) waters, others migrate up rivers to a
variety of fresh water habitats, and still others, as they mature, will
show inter-habitat movement patterns (Jessop et al. 2002, pp. 217-218;
Morrison et al. 2003, pp. 90-92; Cairns 2006a, p. 2; Thibault et al.
2005, p. 36; Lamson et al. 2006, p. 1567; Daverat et al. 2006, p. 2).
Juvenile mortality. Information on mortality rates for all of the
life stages is limited. In Jessop (2000, p. 514), the recruitment of
elvers to the East River, Chester, Nova Scotia, during May through July
was estimated by mark-recapture population estimates to be 960,000
elvers. The population size following migration to recapture sites
about 1.3 kilometers (km) upstream during late July-October was 2,894
elvers. These data indicate high juvenile mortality rates, in this case
at a rate of 99 percent. This high mortality was attributed to the
effects of low pH (4.7-5.0), high initial elver density (4.7 elvers/
m\2\) (which may lead to predation, including cannibalism, starvation,
and competition for space), and predation by resident, presumably
older, eels. V[oslash]llestad and Jonsson's (1988 in Jessop 2000, p.
523) research indicates that eel mortality in fresh waters is density-
dependent when elver numbers exceed a certain abundance. Although it is
not certain if early juvenile mortality is this high throughout the
range of the species, this supports the observation, according to
Jessop, that oceanic conditions may deliver relatively high quantities
of elvers to rivers, such as those along the south shore of Nova Scotia
(Jessop 1998 in Jessop 2000, p. 523), even to the point that elver
abundances too great for habitat capacity can occur (Jessop 2000, p.
523). Surviving juvenile eels mature into fully pigmented ``yellow
eels.''
Mortality rates likely decrease with size. One study in Prince
Edward Island, Canada, calculated loss from the population due to
mortality and emigration. Estimates of loss in American yellow eels
from the Prince Edward Island study are reported at 22 percent, with
mortality rates decreasing to 12 to 15 percent as the juvenile yellow
eels age (Anonymous 2001 in Morrison and Secor 2003, p. 1498), likely
due to lower mortality from predation and starvation as size increases.
Juvenile diet. The enormous dietary breadth of eels reflects their
great adaptability with respect to nearly all conditions of water
bodies. Yellow eels are opportunistic, consuming nearly any live prey
that can be captured. Smaller eels eat benthic invertebrates; larger
eels include mussels, fish, and even other eels in their diet. Yellow
eels also adapt to seasonal changes, decreasing intake or ceasing to
eat during the winter. Eels can also respond to local abundances of
appropriately sized prey through the seasons (Tesch 2003, pp. 152-163).
This adaptable diet allows for resource partitioning as well as the
ability to withstand changes in local environmental conditions and the
ability to occupy a geographically wide variety of habitats.
Density-dependent dispersion. As young eels begin to grow, density-
dependent competition promotes eels to disperse into less crowded areas
(Feunteun et al. 2003, pp. 201-204; Ibbotson et al. 2002 in Knights et
al. 2006, p. 10). Aggressive interactions at high density inhibit
feeding and growth, but stimulate dispersive swimming activity in
smaller eels (Knights 1987 in Knights et al. 2006, p. 10), the latter
likely as a defense against predation. As size differences in these
juveniles increase, cannibalism can also be an important cause of
mortality (Knights 1987 in Knights et al. 2006, p. 10). Density
dependent dispersion ensures wider distributions, further minimizing
intra-specific competition. Benefits of density dependent dispersion
include selection of optimal habitat productivity and temperature,
lower predation risks, rapid colonization or re-colonization of
habitats, and avoidance of inter-specific competition. Larger
individuals farther upstream tend to become more sedentary and occupy
territories, densities of eels decline, and females predominate
(Feunteun et al. 2003, p. 201).
Distribution clines. It has been suggested that there are
latitudinal clines in eel distribution related to river typologies. For
example, the American eel tends to extend farther inland in southerly
lowland drainages compared to distributions in the shorter and steeper
post-glacial stream systems in the Northeast (Jessop et al. 2004 in
Knights et al. 2006, p. 11). Smogor et al. (1995, p. 799) and Knights
(2001 in Knights et al. 2006, p. 8) have documented decreases in
densities with increasing distance from the Continental Shelf in a
predictable pattern, likely as a result of density dependant dispersion
and mortality due to predation. Although mean watershed densities
decrease by an order of magnitude with distance inland from the
Continental Shelf, mean biomass only declines by about 50 percent
because mean body weight and eel length increase (and hence relative
fecundity). This, according to Knights et al. (2006, p. 10), helps
maintain biomass relative to carrying capacity. Machut (2006, p. 13)
indicates that as barrier intensity increases, so does eel growth above
the barrier. Recent research (Knights et al. 2006, pp. 11-13) has
documented that as eel density decreases, the proportion of females
increases, which, assuming females are the limiting sex, would be,
according to Knights et al. (2006, p. 13), a compensatory mechanism
during times or in areas of low density.
Sexually Maturing Life History Stage
Sex determination. There are no morphologically differentiated sex
chromosomes in the American eel (McCleave 2001a, p. 803). Prior to
sexual differentiation, eels are intersexual, meaning they can develop
into either sex. It is only when yellow eels reach a length of about
20-35 cm that it is possible to distinguish males from females
visually, and there is considerable variation in age and size at
differentiation. The determination of sex is likely influenced by
environmental factors, including eel densities (Tesch 2003, pp. 43-46).
Studies indicate that as the density of eels in a particular area
increases the number of male eels increases; decreasing density favors
more females. It has been argued by Knights et al. (2006, p. 13), that
an advantage of this life history strategy is that when recruitment
declines, so will density and tendencies to migrate far upstream in
rivers. In turn, this will lead to relative increases in the number of
(larger) females and hence compensatory increases in fecundity. This
may take a number of generations (and hence decades) to manifest
itself, but this strategy confers enormous benefits in the face of
threats, past, present and future, such as tectonic events and changes
in ocean currents and climate (Knights et al. 2006, p. 13).
Silvering. After a number of years, the yellow eels begin
metamorphosis. Beginning at 3 years old and up to 24 years, with the
mean becoming greater with increasing latitude (e.g., 6-16 years in the
Chesapeake Bay region; Helfman et al. 1987, pp. 44-45; and 8-23 years
in Canada; Cairns et al. 2005, p. 11), yellow eels metamorphose into
``silver eels'' (Cairns et al. 2005, p. 13). This metamorphosis from
bottom-oriented yellow eels to silver eels (termed ``silvering'') is a
key physiological event
[[Page 4971]]
preparing these future spawners for oceanic migration and reproduction
(van den Thillart et al. 2005, p. 12).
Environmental factors may play a role in the triggering of
silvering. Habitat conditions, such as food availability and
temperature, will influence the size and age of silvering eels via
growth conditions. Thus, variation in length and age at maturity can
occur in different habitats (e.g., freshwater habitat versus estuarine
habitat) within a restricted geographic range and over larger
geographic scales as well.
The length of the growing season and the temperature are negatively
correlated with latitude, so age at maturity is strongly correlated
with latitude (McCleave 2001a, p. 803). Characteristics of silver eels
vary across the species' range. Eels from northern areas, where
migration distances are great, show slower growth and greater length,
weight, and age at migration, preparing them, it could be assumed, for
the longer migration.
Indeed, favorable growth conditions cause eels to silver more
rapidly (V[oslash]llestad and Jonsson1988 in Jessop 2000, p. 522;
V[oslash]llestad 1988 and 1992 in van den Thillart 2005, p. 56; De Leo
and Gatto 1995 in van den Thillart 2005, p. 56) such as is the case in
aquaculture, under experimental conditions (Tesch 1991 and Beullens et
al. 1997 in van den Thillart et al. 2005, p. 56), or in brackish water
and at low latitudes (Lee 1979 and Fernandez-Delgado et al. 1989 in van
den Thillart et al. 2005, p. 56). For example, Morrison et al. (2003,
p. 95-96) found annual growth rates in brackish water were two times
higher than growth rates of eels that resided entirely in fresh water.
Also American eels in U.S. southern Atlantic coast waters develop into
silver eels about 5 years sooner than northern populations (Hansen and
Eversole 1984, p. 4; Helfman et al. 1984, p. 139), likely as a result
of warmer, more stable water conditions (Helfman et al. 1984, p. 138).
Variation in maturation age benefits the population by allowing
different individuals of a given year class to reproduce over a period
of many years, which increases the changes of encountering
environmental conditions favorable to spawning success and offspring
survival. For example, variability in the maturation age of eels born
in 2006 may result in spawners throughout 2010-2030, during which time
favorable environmental conditions are likely to be encountered at
least once.
Additionally, males and females differ in the size at which they
begin to silver. Eels appear to need to reach a certain size to begin
the silvering process, with this size increasing with age (thus,
rapidly growing eels will silver at smaller sizes than slow-growing
eels). In males, silvering happens at a very early stage, at a size
typically greater than 35 centimeters (cm). In females, silvering
happens at a size greater than 40 to 50 cm (Goodwin and Angermeier
2003, p. 530; van den Thillart et al. 2005, pp. 31, 55).
Actual metamorphosis is a gradual process occurring during the
summer, and in the fall eels metamorphosing in preparation for
migration back to the spawning grounds have a silvery body color,
enlarged eyes and nostrils, and a more visible lateral line (Dave et
al. 1974; Lewander et al. 1974; Pankhurst 1983; and Barni et al. 1985
in van den Thillart 2005, p. 12). As the structure and metabolism of
the liver changes, the swim-bladder also changes, allowing for
increased gas deposition rates and decreased loss of gas (McCleave
2001a, p. 804).
A drop in temperature appears to trigger the final events of
metamorphosis (gut regression and cessation of feeding), which will
lead to migratory movements under the appropriate environmental
conditions. It is theorized that responding to a drop in temperature
would help to synchronize out-migrating eels, thus increasing their
chances of reaching the Sargasso Sea simultaneously. Conversely,
increasing temperatures, delays in migration, or possibly low fat
content will cause eels to start feeding again and to revert to a
yellow resident stage. This would happen in the natural environment if
eels did not reach the sea before the end of the migrating season. It
has been observed that even after eggs and sperm have developed, eels
are capable of gut regeneration and feeding (Fontaine et al. 1982,
Dollerup and Graver 1985, in van den Thillart et al. 2005, p. 56). Van
den Thillart et al. (2005, p. 56) confirmed that silvering may occur
more than once in the lifetime of an eel. It has been said that this
phenomenon would explain the extreme variability in age and size of
silver eels. It has been hypothesized that conditions encountered
during oceanic migration, such as the high pressure they would
experience at depth in the open ocean, may complete the sexual
maturation of eels (Fontaine et al. 1985 in van den Thillart et al.
2005, p. 13).
Outmigration Life History Stage
Energy requirements. To successfully complete the migration from
the continent to the Sargasso Sea (out-migration), great endurance and
an extensive fat reserve are required. Larger, fatter eels have an
advantage over smaller eels in reaching the Sargasso Sea and having
sufficient energy stores to reproduce. Eels are very efficient swimmers
(eels swim approximately four to six times more efficiently than
salmonids), and larger eels appear more efficient than smaller eels
(van den Thillart et al. 2005, pp. 106-107). Also, larger eels usually
have larger fat stores per body weight. Silver eels have ceased
feeding, and use their stored fat for energy during their migration and
for completing gonadal growth. In a study conducted on European eel,
the most recent estimate of necessary energy (fat) needed to
successfully complete the migration to the Sargasso Sea from Europe and
spawn is 20 percent fat reserves, of which 13 percent is for transport,
and an additional 7 percent for completing gonadal growth. In European
silver eel, about 50 percent of the eels studied had a fat percentage
of 20 percent (van den Thillart et al. 2004 in van den Thillart et al.
2005, p. 109).
It is unknown if American eels require 20 percent fat reserves.
American eels travel a shorter distance to reach the Sargasso Sea than
do European eels. Actual distances, routes, and depths of migration for
adult eels are unknown. Distances traveled by migrating silver American
eels likely vary from under 1,500 km to over 4,500 km, shorter than the
5,000 km to 7,000 km likely traveled by European eels. An American eel
maturing in the Mississippi River, Louisiana, would travel a distance
of over 2,200 km; from South Carolina, 1,440 km; from Chesapeake Bay,
Virginia, 1,550 km; from Newfoundland, Canada, over 2,800 km (McCleave
2001a, p. 805); and from western Lake Ontario, over 4,500 km. Silver
eels, it has been hypothesized by Knights (2003, p. 240), may follow
the deep currents (for American eel, the Deep Western Boundary Current)
to return to the Sargasso Sea. However, others believe the American eel
migrates in the upper portions of the ocean (see van Ginneken and Maes
2005, pp. 385-387; Tesch 2003, pp. 206-207).
Fecundity. Fecundity also varies with size. Fecundity increases
exponentially with length, ranging from about 0.6 million to almost 30
million eggs depending on the size of the female (McCleave 2001a, p.
804). As an example, in the lower Potomac watershed, the average silver
female length of 734 mm would produce 2.7 million eggs; farther up the
watershed the average silver female length of 870 mm would produce 5.2
million eggs (Goodwin and Angermeier 2003, p. 533). Fecundity is also
linked to the habitat which the eel occupies. In an eel
[[Page 4972]]
farm growth experiment, favorable nutrition was one of two factors (the
other being genetic heterozygosity, where 2 different alleles are at
one loci) producing eels with a high reproductive capacity (van den
Thillart et al. 2005, p. 232). This high fecundity is thought to
compensate for very high larval mortality (reported by Knights et al.
2006, p. 4, as most probably well in excess of 99 percent).
Spawning. Spawning takes place in the Sargasso Sea (Schmidt 1922 in
Bo[euml]tius and Harding 1985, p. 122). Here, in the area where
northern and southern waters meet, it has been hypothesized that there
is some unidentified feature of the surface water (perhaps the abrupt
horizontal temperate change of the frontal zone located within the
subtropical convergence) that serves as a cue for migrating adults to
cease migration and begin spawning (Kleckner et al. 1983, p. 289;
Kleckner and McCleave 1988, pp. 647-648; Tesch and Wegner 1991 in
Miller 2005, p. 1). Spawning has not been witnessed by humans, but the
assumption is that adult eels die after spawning.
Range
The extensive range of the American eel includes all accessible
river systems and coastal areas having access to the western North
Atlantic Ocean and to which oceanic currents would provide transport.
These drainages and coastal areas are along more than 50 degrees of
latitude (from 5[deg] to 63[deg]) of the western North Atlantic Ocean
coastline, from Northern Brazil/Venezuela to southern Greenland (Scott
and Crossman 1973, pp. 624-625; Tesch 2003, pp. 92-97; Helfman et al.
1987, p. 42), including most Caribbean Islands and Bermuda, the eastern
Gulf of Mexico and associated drainages including the extensive
Mississippi River watershed (e.g., Mississippi River, Ohio River,
Tennessee River, Arkansas River, and Missouri River) as far north as
Minnesota, the Gulf of St. Lawrence and the associated rivers, and Lake
Ontario and associated drainages. It is believed that the eel was
absent from the waters of Lakes Erie, Huron, and Superior before the
completion of the Welland Canal in 1829 (Patch 2006, p. 2). In 1878,
the Michigan Fish Commission planted young eels in southern Michigan
waters, and for more than a decade, beginning in 1882, the Ohio Fish
Commission released young eels throughout Ohio, including drainages to
Lake Erie (Trautman 1981, pp. 192-193) (Figure 1). This extensive range
should provide the American eel with a buffer against adverse
conditions, as spawners would still be coming from areas not
experiencing adverse conditions, and would, due to random dispersal and
relatively homogeneous genetic structure, be capable to successfully
re-colonize areas once the threat has abated.
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It has been reported in other documents that Bo[euml]tius and
Harding (1985) estimated that the American eel range covers more than
10,000 km of coastline; however, we could not locate this information.
Utilizing current mapping technology, our estimate of the available
coastline (including barrier islands) from Maine to Texas (Atlantic and
Gulf coast) is 29,612 km (Castiglione 2006, p. 1).
As a result of oceanic currents, the majority of the American eel
population is located along the Atlantic seaboard of the United States
and Canada. The historic and current distribution of the American eel
within its extensive continental range is well documented along the
United States and Canadian Atlantic coast, and the SLR/LO. The
distribution is less well documented and likely rarer, again due to
currents, in the Gulf of Mexico, Mississippi watershed, and Caribbean
Islands, and least understood in Central and South America.
Habitat
The American eel is said to have the broadest diversity of habitats
of any fish species (Helfman et al. 1987, p. 42) by occupying multiple
aquatic habitats. From an evolutionary standpoint, this generalist use
of habitats is favored in fluctuating environments, while specialists
excel under constant or slowly changing environmental conditions
(Richmond et al. 2005, pp. 279-280).
During their spawning and oceanic migrations, eels occupy
saltwater, and in their continental phase, they use all salinity zones:
Fresh, brackish, and marine (for detailed habitat use by life stage,
see Cairns et al. 2005). Eels occur in waters highly productive to fish
species and those that are not, and from waters of near tropical
temperatures to waters that are seasonally ice-covered (McCleave 2001a,
p. 800).
Growing eels are primarily benthic, utilizing substrate (rock,
sand, mud) and bottom debris such as snags and submerged vegetation for
protection and cover (Scott and Crossman 1973, p. 627; Tesch 2003, pp.
181-183). In Canadian waters, American eels hibernate in mud during the
winter. Wintering areas include fresh water, brackish estuaries, and
bays with full strength salt water (Cairns et al. 2005, p. 3.4.6).
Barring impassable natural or human-made barriers, eels occupy all
freshwater systems, including large rivers and their tributaries,
lakes, reservoirs, canals, farm ponds, and even subterranean springs.
The anquillid (eel-shaped) body form allows for climbing when at young
stages and under certain conditions (e.g., rough surfaces), allowing it
to pass up and over some barriers encountered during upstream
migrations in freshwater streams (Craig 2006, pp. 1-4). Eels are able
to survive out of water for an exceptionally long time (eels can meet
virtually all their oxygen needs through their skin), as long as they
are protected from drying (for which their ability to produce mucus is
of great adaptive significance), and eels have been seen using overland
routes (while moist) when they encounter a barrier, explaining their
entrance into landlocked waters (Tesch 2003, pp. 184-185) and their
presence above numerous dams and weirs (USFWS 2005b, pp. 16-18).
Abundance. Abundance (density) and distribution of eels within
habitats may be a function of distance from the ocean and may not be
related to habitat features (Smogor et al. 1995, pp. 796-797) (see also
Density-Dependant Dispersion). According to Smogor et al. (1995, p.
799) when examining Virginia streams, they found little connection
between habitat features and the distribution and abundance of American
eels at least at a large scale. Their results, they suggest,
demonstrate a diffusion pattern of eel occurrence. This lack of eel-
habitat relations (at least at a large scale) within freshwater systems
suggests that comparison of abundance for purposes of identifying
quality habitat would be misleading. Rather, it has been suggested
(USFWS 2006, pp. 13-14, 22) that the reproductive contribution of an
area to the total American eel population would be the best manner of
identifying quality habitat; however, reproductive contribution
estimates from throughout the range of the American eel are not
available. Examples of densities provided below are to illustrate the
variation of densities, not for comparison of habitat importance.
Machut (2006) summarized freshwater and brackish water density research
and standardized to eel densities per 100m\2\. In Lake Champlain,
Vermont, densities ranged from 2.32-6.36 eel/100m\2\ (LeBar and Facey
1983 in Machut 2006, p. 50). In a tidal creek, Georgia, densities
ranged from 1.82-2.32 eel/100m\2\ (Bozeman et al. 1985 in Machut 2006,
p. 50). A Massachusetts salt marsh yielded densities of 8.46-9.28/
100m\2\ (Ford and Mercer 1986 in Machut 2006, p. 50). In Machut's own
study in the Hudson River freshwater tributaries densities ranged from
0.28-155.06/100m\2\ (Machut 2006, p. 50), while in brackish waters
Morrison and Secor (2003 in Machut 2006, p. 50) reported densities of
0.03-0.24/100m\2\ . In four Maine freshwater rivers, densities ranged
from 1.80-35.40/100m\2\ (Oliveira and McCleave 2000, p. 144). Recent
population estimates of juvenile eels (mostly elvers) on the South Anna
River in Virginia were 1.88 eels/100m\2\. On the North Anna River,
where the eels were smaller, the population estimate was greater at
4.48/100m\2\ (Odenkirk 2006, p. 1). No estimates of abundance or
density are yet available for marine waters.
Habitat associations at a finer scale, such as areas within a lake,
have recently been researched by Cudney (2004). In her studies, she was
able to associate certain short-term habitat conditions, such as non-
stagnant waters and to a lesser extent long-term habitat features such
as water depth and percent organic matter, to a higher probability of
eel capture (Cudney 2004, pp. 57-60).
Facultative Catadromy. Contrary to the earlier dominating paradigm
that the eel growth phase is restricted to fresh water, it has been
suggested that brackish (or estuarine) waters produce eels that grow
faster, mature earlier, and emigrate as silver eels sooner than eels in
fresh water, and that some eels complete their life cycle in brackish
or marine waters without ever entering fresh water. Facultative
catadromy, therefore, refers to migrations into fresh water as not
being obligatory (Tsukamoto and Arai 2001, p. 2651).
Morrison et al. (2003, p. 94) found annual growth rates in brackish
water were two times higher than growth rates of eels that resided
entirely in fresh water. The mechanism for this higher growth in
brackish water is not well understood. Possible causes include an
increase in quality or quantity of food, increase in habitat quality
(Helfman et al. 1987 in Morrison et al. 2003, p. 94), lower resting
metabolism resulting from living in near-isoosmotic (same salinity
within the eel as the external environment) conditions, increased water
temperature (which reduces the amount of time that eels are dormant
during winter) (Walsh et al. 1983 in Morrison and Secor 2003, p. 1499),
reduced effects from parasites, decreased predation, or decreased
intra- or inter-specific competition. Morrison and Secor (2003, p.
1499) hypothesized that the higher brackish-water eel growth measured
on the Hudson River is general to most large North American estuaries.
Two other studies became available during our status review, which
provided data on use by eels of marine habitats during the eel growth
phase (Daverat et al. 2006; Lamson et al. 2006). The first study, by
Daverat et al. 2006,
[[Page 4975]]
looked at habitat plasticity in the American, European, and Japanese
eel (A. japonica;) the second, by Lamson et al. (2006), at American eel
in Canadian waters. In the first study, habitat use consisted of either
residency in one habitat (fresh, brackish, or marine) or movements
between habitats. Seasonal or minor (1 or 2) movement patterns were
seen from brackish water to fresh water and vice versa. Single habitat
switch events occurred, usually between 3 and 5 years of age.
``Nomadic'' movement between water masses of different salinity was
common; the differences in productivity between freshwater and brackish
habitats (and the resulting lower growth of eels in temperate
freshwater sites), the authors state, might explain this phenomenon.
Occurrence of eels with no freshwater experience was demonstrated, but
such eels accounted for a smaller proportion of the overall sample than
did eels with some (even brief) freshwater experience. Another
interesting result was that eels tend to prefer brackish and marine
habitats for feeding at the northern extremes of their range. The
authors also suggest that this high degree of habitat use plasticity
suggests a remarkable ``bet hedging'' strategy for angullids as a group
(Daverat et al. 2006, p. 11). In the second study, conducted on
American eels in Canada, marine (saltwater) resident eels were the
dominant migratory contingent of eels in saltwater bays (85 percent).
Resident eels were established in salt and freshwater habitats by the
year after their arrival in continental waters. Eels that shifted
between habitats increased their rate of inter-habitat shifting with
age. This study also showed that plasticity of habitat usage is the
norm among eels, and that the American eel life cycle can be completed
in marine waters (Lamson et al. 2006, p. 1572). A study of Japanese eel
found that estuarine (43 percent) and marine (40 percent) eels
contributed more spawners than did eels from freshwater areas (17
percent), with some seasonal differences. Additionally, the study noted
that eels from all three habitats began their marine spawning migration
at about the same time. The implication here is that eels from all
habitats can mix together during spawning migration and potentially
contribute to the next generation (Kotake et al. 2005, p. 220). In
Tsukamoto et al's evolutionary perspective, the authors hypothesize,
based on Inoue 2001, that molecular evidence might suggest that
catadromous Anguillidae come from deep-sea eels, with a migration loop
that extended to coastal waters and incidentally visited estuaries;
these eels may have eventually obtained a reproductive advantage
because of higher food availability in estuaries than in freshwater
(Tsukamoto et al. 2002 in Miller 2005, p. 2).
According to Lamson et al. (2006, p. 1568), [Eacute]deline and
[Eacute]lie (2004) reported that European glass eels have distinct
individual salinity preferences. This implies that young eels separate
into migratory contingents upon arrival on the coast, with salt-seeking
eels remaining in marine waters while fresh-seekers ascend into fresh
waters.
The benefits of facultative catadromy include resource
partitioning, by minimizing intra-specific competition between life
stages and cannibalism of young by adults. Additionally, there are
growth-temperature benefits, as shallow brackish and fresh waters
(especially still waters) will heat up faster in the spring and summer
than marine waters. Although not tested by any large-scale quantitative
distribution data, the effective reproductive contribution of brackish/
marine habitats may be substantial (Tsukamoto and Arai 2001, p. 275;
Jessop 2002, p. 228; Kotake et al. 2005, p. 220; Knights et al. 2006,
pp. 12-13; Cairns 2006a, p. 1). Densities may be relatively low in
coastal waters, but for European eel in England and Wales, Knights et
al. (2001 in Knights et al. 2006, p. 13) calculated that estuarine and
shallow coastal waters (estimated at 5,000 km\2\) exceed that of
freshwater (1,035 km\2\).
Clinal Variations. American eels show clinal variation (gradual
changes over a geographic area) in their growth rates and size at
maturity between the southern and northern portions of their range.
Although mostly a warm water species, Anguillids are eurythermal
(tolerant of a wide range of temperatures) and can survive extremes by
migratory and cryptic behaviors. Even so, growth seasons inevitably
shorten with increasing latitude. This produces clines as you move
north of slower growth rates and larger size at maturity, thus
retaining relative fecundity with increasing latitude (Knights et al.
2006, p. 6).
Population Status
Typically an evaluation of population status for a 12-month finding
would include a rangewide estimate of population size and information
on the demographic structure of the population and subpopulations as
well as population trend information in context with historical data,
and possibly an evaluation of the long-term viability of the current
population through a population viability analysis model.
No rangewide estimate of abundance exists for the American eel.
Information on demographic structure is lacking and difficult to
determine because the American eel is a single population (panmixia)
with individuals randomly spread over an extremely large and diverse
geographic range, with growth rates and sex ratios environmentally
dependent. Because of this unique life history, site-specific
information on eels must be evaluated in context with its significance
to the entire population. Determining population trends is challenging
because the relevant available data is limited to a few locations that
may or may not be representative of the species' range and little
information exists about key factors such as mortality and recruitment
which could be used to develop an assessment model. Furthermore, the
ability to make inferences about species' viability based on available
trend information is hampered without an overall estimate of eel
abundance. Despite these challenges we have determined the species
currently appears stable, as we explain below.
The Stock Assessment Committee of the ASMFC recently assessed the
``stock status'' of the American eel (ASMFC 2006a), and this assessment
was subsequently reviewed by an independent panel of scientists (ASMFC
2006b). The Stock Assessment Committee concluded that the status of the
stock is uncertain as a result of insufficient data. Their conclusion
was based on the review of nine indices, two were fisheries-dependent
and seven were fisheries-independent. Of these indices, one index shows
an upward trend over time, one shows no trend, and the remaining seven
show a downward trend (ASMFC 2006a, p. x). The committee hypothesized
that the indices exhibiting a downward trend suggest that the stock is
at or near documented low levels. The glass eel data from two Atlantic
Coast sites were not used, and the panelists who reviewed the stock
status felt that these indices were a valuable asset. These panelists
interpreted the absence of a declining trend in glass eel abundance in
either series over the last 14 to 15 years as the only positive
indicator that recruitment, at least to the glass eel stage to these
portions of the coast, had not declined in concert with some of the
yellow eel indices (ASMFC 2006b, p. 4). The ASMFC stock status
assessment has limited value in the 12-month finding because the
purpose of the ASMFC stock status assessment is to inform management of
the commercial
[[Page 4976]]
American eel fishery by determining allowable harvest, not to look
specifically at long-term viability of the species.
Recently Canada completed its review of the American eel status
within Canadian waters as part of the Committee on the Status of
Endangered Wildlife in Canada's (COSEWIC) review for possible listing
under their version of the Endangered Species Act, known as Species At
Risk Act (SARA). This review also was more similar to a stock status
assessment than a population viability analysis. They determined that
indicators of the status of the total Canadian component of this
species were not available. Their evaluation of the data (indices of
abundance in the upper SLR/LO declined by approximately 99 percent
since the 1970s and four out of five time series from the lower St.
Lawrence River and Gulf of St. Lawrence declined) led them to apply the
Special Concern designation (COSEWIC 2006, p. III). Because the COSEWIC
review focuses on the status of American eels in Canadian waters, the
report also discussed the ``rescue effect.'' In the hypothetical
scenario where the American eel became depleted or extirpated within
Canadian waters external components would ``rescue'' the species in
Canada. These external components refer to the young eels from the
Sargasso Sea that are from American eels whose parents originated from
U.S. waters, and experience random dispersal due to oceanic currents
which would continue to deposit leptocephali into Canadian waters
(COSEWIC 2006, p. 43).
Together, however, these reports provide a more recent presentation
of the individual data sets than was available in the stock status
report by the International Council for the Exploration of the Sea or
ICES (2001, pp. 51-52), which was the only stock assessment available
at the time of the 90-day finding published on July 6, 2005 (70 FR
38849). As a result of these factors, our assessment of the American
eel population status will utilize the available information to: (1)
Provide context of historical reports and current landings data as a
surrogate for absolute abundance estimates; (2) evaluate the data from
each different life stage and the significance of that life stage when
evaluating the population status of the species including trend data in
specific geographic areas and each area's significance to the
population status of the species; and (3) evaluate the data to
determine if there is a sustained downward trend in a location or
locations that would be considered representative of the entire range.
Together these will provide the basis for our assessment of whether the
species is currently being impacted by threats to the degree that the
American eel meets the definition of threatened or endangered. In
addition, in the 12-month finding we also take into account the
species' life history characteristics and compensatory mechanisms (see
Background and for further discussion).
(1) Historical and Current Information
Historically eels were a significant winter food source for Native
Americans (see Casselman 2003, for a compilation of prehistoric and
historic information from the United States and Canada) and later for
European settlers. However, qualitative rather than quantitative
information is all that is available from these early times. In the
early 1900s, records from commercial fisheries began to appear. For
example, weirs at Oneida Lake, Canada, caught 100 metric tons (220,000
pounds) annually of emigrating eels (Adams and Hankinson 1928 in
Casselman 2003, p. 260). Casselman cites the subsequent construction of
dams and canals, which restricted access to the lake as the reason for
its eventual extirpation from Lake Oneida. Given the size of the
harvest, Casselman concludes that recruitment immigration in the past
was much more extensive and probably much greater than in recent times.
Although the current status of American eels cannot be described in
absolute terms because rangewide estimates of abundance do not exist
(ASMFC 2006a, p. viii; ASMFC 2006b, pp. 3, 13), we provide below recent
ASMFC and COSEWIC landings data (long-term fishery independent indices
do not exist) that indicate that the order of magnitude of yellow and
silver phase eel abundance is probably in the many millions. In the
past decade, commercial fisheries in the United States and Canada have
landed approximately 800 metric tons (1.8 million pounds) of yellow and
silver phase American eels annually (ASMFC 2006a, p. 82). These
landings data provide a general sense of eel abundance if we make
assumptions about the size and relative proportion of eels that are
landed. Specific data on the size of eels harvested were not available,
but 45 cm was considered a reasonable estimate (Cairns 2006b, p. 1).
The average weight of American eels 45 cm long is 156 grams (g) (Cairns
2006b, p. 1), which indicates that 800 metric tons is equivalent to
over 5 million eels. Assuming a high capture efficiency of 25 percent
for the eel fisheries (Caron et al. 2003, p. 235) suggests that the
post-fishery abundance (i.e., 75 percent are not captured) of yellow
and silver phase eels is greater than 15 million within the areas
fished. Given that not all areas within the range of the eel are
fished, this number would represent a minimum. These calculations are
not intended to be used as a formal estimate of population size, but
simply to provide the context that large American eels, throughout
their range, likely number in the many millions.
(2) Trend Data From Different Life Stages and Locations
Trends in American eel abundance from fishery-independent indices
(e.g., data from surveys and research) varied among locations and life
stages during the past 10-25 years. Data from yellow eels (which may
include silver eels) and glass eels (and elvers) are presented below.
Yellow eel. Four indices (including Maritime rivers in Canada and a
standardized U.S. coastwide yellow eels abundance index) did not
exhibit trends (ASMFC 2006b, p. 3). Indices from freshwater and tidal
sites distributed from the mid-Atlantic region north to Canada and the
St. Lawrence River indicated a statistically significant declining
trend in yellow eel abundance at three sites. Two of these indices,
Lake Ontario and the Chesapeake Bay index, had strong and statistically
significant declining trends over the recent 1994 to 2004 time period,
with 10-year declines in the order of 50 percent in the Chesapeake Bay
index to 99 percent in the Lake Ontario indices (ASMFC 2006b, p. 3).
Smaller declines (15 percent) were reported in the St. Lawrence estuary
(COSEWIC 2006, p. vi). Recent data suggest that declines may have
ceased in some Canadian locations; but the positive trends in some
indicators for the Gulf of St. Lawrence are, the COSEWIC report states,
too short to provide strong evidence of an increasing trend (COSEWIC
2006, p. 58).
It should be mentioned that yellow eel indices may reflect local or
regional impacts, such as impacts from harvest or turbine mortality
(see Factors B and E for further discussion). Additionally, yellow eels
have not yet been subject to mortality that may occur during their
oceanic outmigration to the Sargasso Sea. Therefore, yellow eel indices
are not the best indicator for estimating annual reproductive success.
Evaluation of the Significance of Upper SLR/LO. The extreme decline
in eels migrating up to the upper SLR/LO, as tallied at the Moses-
Saunders eel ladder, has focused attention on the potential impact of
that decline to the overall status of the American eel;
[[Page 4977]]
however, COSEWIC states that a rigorous way to quantify this impact to
the overall population has yet to be developed (COSEWIC 2006, p. 35).
The suggestion is that the reproductive contribution to the overall
American eel population from the upper SLR/LO may be disproportionately
larger than from other freshwater portions of the range because the
American eels in the upper SLR/LO are almost exclusively female and
highly fecund (producing many eggs) due to their large size, and the
watershed is of considerable size. Two methods for estimating the
relative reproductive contribution were presented in the COSEWIC report
(2006, pp. 35-41), but both methods, they state, are based upon
questionable assumptions and large uncertainties that reduce confidence
in the results. Additionally, contributions from marine and estuarine
waters were not considered in the analysis. According to COSEWIC some
sources of uncertainty suggest that it is more probable that the
methods overestimate, rather than underestimate, the reproductive
contribution of the St. Lawrence River basin (COSEWIC 2006, p. 41).
Glass eels. Indices of glass eel recruitment at the only two U.S.
sites with long-term data (North Carolina and New Jersey) did not
exhibit a declining trend over the last 14-15 years (ASMFC 2006b, p.
4). Recruitment estimates into Canadian rivers are available for two
Nova Scotian sites. The East River, Sheet Harbour, abundance series is
the longest elver series available for the species. Annual recruitment
varied without any upward or downward trend from 0.1 to 0.5 million
elvers between 1989 and 1999 (Jessop 2003a in COSEWIC 2006, p. 28). In
the East River, Chester, the total run of elvers peaked at 1.7 million
in 2002. Since the overlap periods of the two series are strongly
correlated, a combined index of 13 years was interpreted in the COSEWIC
report. Elver recruitment showed inter-annual variability, but no
indication of decline between 1989 and 2002 (COSEWIC 2006, p. 28).
Glass eel counts, also called recruitment indices, are the best
measure we have to annual reproductive success (see section immediately
below).
(3) Evaluation of Trend Information
Of the available index data for the different American eel life
history stages, we have determined that glass eel indices best
represents the species status rangewide. Although we do not have glass
eel indices from the entire range, the random nature of the
leptochephali dispersal allows us to consider these data representative
of the reproductive success of the species. As described above, there
is not evidence of a sustained downward trend of these glass eel
indices; therefore, we conclude that the American eel is not undergoing
a sustained downward trend at a population level.
In summary, the best available scientific and commercial
information indicates that despite a population reduction over the past
century, eels remain very abundant and occupy diverse habitats over an
exceptionally broad geographic range. Because of the species' unique
life history traits areas which have experienced depletions may
experience a ``rescue effect'' allowing for continued occupation of
available areas without concern for genetic fitness. Trends in
abundance over recent decades vary among locations and life stages,
showing decreases in some areas, and increases or no trends in other
areas. Limited records of glass eel recruitment do not show declines
that would signal recent declines in annual reproductive success or the
effect of new or increased threats. Taken as a whole, a clear trend
cannot be detected in species-wide abundance during recent decades, and
while acknowledging that there have been large declines in abundance
from prehistoric and historic times, we have determined the species
currently appears stable.
Summary of Background
The American eel is an extremely wide ranging species, continuing
to occupy most of its historic range. This species is highly plastic in
both its behavior and physiology, being able to occupy habitats ranging
from sea water to freshwater lakes. This species also exhibits adaptive
behaviors such as switching between habitats and diets. These life
history characteristics provide the American eel with the ability to
withstand a wide range of, and changing, environmental conditions. The
best available scientific and commercial information does not indicate
any sustained declining trend in the American eel population.
Previous Federal Actions
On July 6, 2005, we published a 90-day finding (70 FR 38849) which
found that the petition to list the American eel presented substantial
scientific and commercial information indicating that listing the
American eel may be warranted. That document initiated a status review
to determine if listing the species was warranted. This 12-month
finding provides the results of that status review.
Summary of Factors Affecting the Species
Section 4 of the Act (16 U.S.C. 1533), and implementing regulations
at 50 CFR 424, set forth procedures for adding species to the Federal
Lists of Endangered and Threatened Wildlife and Plants. In making this
finding, information regarding the status and threats to this species
in relation to the five factors provided in section 4(a)(1) of the Act
is summarized below. We examined each of these factors as they relate
to the current distribution of American eel.
Regional information was more obtainable from the Atlantic coast,
likely due to the economic interest in the American eel. We have
divided the range of the American eel into seven areas for purposes of
discussion: (1) The Gulf of Mexico (from south Texas to the southern
tip of Florida); (2) The Mississippi watershed (Lake Itasca in
Minnesota to the Gulf of Mexico); (3) The U.S. Atlantic coast (the
southern tip of Florida north to Maine's border with Canada); (4) The
Canadian Atlantic coast (Canadian border north to Labrador, and
including the Gulf of the St. Lawrence); (5) The St. Lawrence River and
Lake Ontario (from the Gulf of the St. Lawrence River to and including
Lake Ontario, abbreviated as SLR/LO); (6) The Caribbean Islands
(Antigua, Barbuda, Bahamas, Cuba, Dominica, the Dominican Republic,
Saint Kitts and Nevis, Saint Lucia, Saint Vincent and the Grenadines,
and Bermuda); and (7) Central/South America (Atlantic coasts of
northern Mexico; south through Guyana, Suriname, and Venezuela; to
northern Brazil).
Addressing Uncertainties
The life history of American eels presents unique challenges to
understanding the biological and environmental processes influencing
eels at the species level. The eel's panmictic nature, wide geographic
range, oceanic spawning, and segregation into freshwater, estuarine,
and marine environments all contribute to the complexity of assessing
status, threats, and whether listing is warranted. With many species,
population dynamics modeling can inform listing determinations, but the
current understanding of American eel population dynamics is
rudimentary due to its complex life history and the paucity of data
available for many key parameters, such as recruitment, growth, and
mortality. A useful conceptual framework for a population dynamics
model has recently been
[[Page 4978]]
developed by a group of eel experts (Angermeier 2005), but quantitative
analysis has been precluded due to a lack of data.
As discussed below in the five factor analysis, much speculation
exists on factors that could negatively affect eels, often based on
effects seen on other species but with little supporting data for eels.
Much of the uncertainty exists because decreased fitness would be
realized during life stages that are currently not possible to assess,
specifically, the time between adult spawning migration and the return
of glass eels to coastal streams. For example, contaminants and swim-
bladder parasites may compromise the health of silver eels during
migration. Contaminants could also contribute to significant early life
history mortality, but these effects are not directly observable.
We considered a number of questions when reviewing the available
information and potential threats to American eel. What is the
population status of American eel and how much caution is warranted?
What is the species' ability to withstand threats and changing
environmental conditions? Would all eels throughout the widely
distributed range of the panmictic population be affected by a given
threat? Is there evidence that indicates a threat has caused
significant population effects, or are effects only speculative? Has
there been a reduction in juvenile (glass eel) recruitment (which would
signal population-level effects)? And if so, does it correlate in time
(temporal correlation) to the appearance of a particular threat or
threats? Answers to these and other questions are important to making a
listing determination.
When addressing uncertainty (not having complete, or in some cases
any, data on one or more of the questions listed above), we employed a
multi-step approach. The first step was to review all available data on
the American eel with regard to uncertainty and determine, for example,
if the data we have regarding an impact at a local or regional level
implies an impact at a population level, and if so, what the likely
response of the population is and in what given time period. If data
for American eel is lacking, then we reviewed data for other Anguillid
species, such as the European and Japanese eel, and determined if the
application of that data was appropriate to the analysis. If
uncertainty still remained high, then we requested individual
assessments from experts regarding the probable implications to the
species given the uncertainties.
In making this finding we examined all the relevant data on
threats, life history characteristics (such as resiliency and
vulnerabilities), and distribution information. We explored all
reasonable conclusions and examined information to support and refute
theories on population level effects, looking at whether the species
was currently showing the effects of any population level threats. A
population level effect is defined for purposes of this finding as an
effect that is acting in a way which puts the persistence of the entire
species at risk. Population-level effects would be demonstrated by a
sustained downward trend in glass eel abundance (recruitment) observed
at index sites that represent a substantial portion of the range. Our
five-factor analysis follows.
Factor A. The Present or Threatened Destruction, Modification, or
Curtailment of the Species' Habitat or Range
In analyzing these threats we assessed: (1) The relative importance
to reproductive contribution of the various habitats occupied by the
American eel during its life stages (such as spawning habitat in the
Sargasso Sea, oceanic migration habitats, fresh water, estuarine and
marine habitats), including which habitats are more likely to produce
males or females, various growth rates, and levels of fecundity; (2)
the threats to these habitats; and (3) the availability of that habitat
to the American eel. Much of the information on the habitats other than
freshwater was not available for the 90-day finding, and the new
information has had a significant effect on our assessment of the
status of the American eel.
Spawning and Ocean Migration Habitat
American eels spawn only in the Sargasso Sea, and the young
produced from that spawning utilize ocean currents to migrate to
continental habitats where they will grow to maturity before again
entering oceanic habitats to migrate back to the Sargasso Sea to spawn.
Therefore, the spawning and ocean migration habitats are of vital
importance to the persistence of this species.
Seaweed harvest was indicated as a possible threat to the American
eel in the ASMFC's Interstate Fisheries Management Plan for the
American eel (FMP) (2000, pp. 6, 34). The seaweed Sargassum is commonly
found floating in the Sargasso Sea and drifting with currents along the
Atlantic coast from Florida to Massachusetts. Harvesting Sargassum, it
was proposed, would affect eggs and leptocephali, if harvesting occurs
where eggs and leptocephali are present.
After analysis of the available data, we conclude that Sargassum
harvest is not a threat to American eel either in the Gulf Stream
current or in the Sargasso Sea because first, studies of larval and
juvenile fishes associated with Sargassum found no American eel larvae
(Settle 1993 in SAFMC 2002, pp. 20-23), and second, according to the
South Atlantic Fishery Management Council (SAFMC), there has been no
commercial harvest of Sargassum reported in U.S. waters since 1997. Any
future Sargassum harvest will be highly regulated because in November
2002, the SAFMC finalized the revised Fishery Management Plan (FMP) for
Pelagic Sargassum Habitat of the South Atlantic Region. This plan
specifies maximum and optimum sustainable Sargassum yield and sets
total allowable catch limits, which severely limit Sargassum harvest
(SAFMC 2002, pp. vi, viii). As such, we have concluded that U.S.
commercial Sargassum harvest is not a threat to the American eel.
Furthermore, there is no information indicating any other threat to the
Sargasso Sea or ocean migration habitats (see Factor E for Oceanic
Conditions), and these habitats remain abundantly available to the
American eel.
Estuarine and Marine Habitat
Estuarine. The importance of estuarine habitat is described by
Helfman et al. (1984, p. 135), Jessop et al. (2002, pp. 84, 228),
Morrison et al. (2003, pp. 93-95, 97), and Knights et al. (2006, pp.
12-13). An estuary is a semi-enclosed coastal body of water which has a
free connection with the open sea and within which sea water is
measurably diluted with fresh water derived from land drainage
tributaries. Estuarine habitat appears to not only be habitat in which
eels may choose to remain during their continental phase, but it is
used by freshwater residents for weight gain. According to Knights et
al. (2006, p. 25), inshore coastal and estuarine mean net primary
productivity (the transformation of chemical or solar energy to
biomass) is greater than that of rivers and lakes. Females inhabiting
estuarine waters, therefore, can provide a greater reproductive
contribution. Estuarine habitat includes a mix of males and females.
Because eels grow faster in estuarine waters than fresh water, the
average age of a female within estuarine waters preparing to spawn is
much younger (9 years of age) than females leaving lake habitats (24
years of age in Lake Ontario). Variation in maturation age benefits the
population by allowing different individuals of a
[[Page 4979]]
given year class to reproduce over a period of many years, which
increases the chances of encountering environmental conditions
favorable to spawning success and offspring survival. Jessop et al.
(2002, p. 228) provides an interesting perspective on the relative
production of silver eels by comparing elvers that spend 1 to 4 years
in the estuary versus elvers that entered the river shortly after
continental arrival. The authors suggested that the relative production
of silver eels was 380 times higher for juvenile eels that spent 1 or
more years in estuarine water, due possibly to lower mortality rates in
the estuary than in fresh water (see Background, Facultative
Catadromy). Helfman et al. (1984, p. 135), even as early as 1984,
recognized the value of estuarine habitat where annual growing
conditions were more favorable. Maximum size was greater in fresh
water, but lengths at a given age were greater in estuaries. Morrison
et al. (2003, pp. 94-95) found that annual growth rates were
approximately 2 fold higher in brackish water when compared to annual
growth rates in fresh water. The theory is that eels which grow faster,
emigrate to spawn earlier.
Although there have been historic losses and degradation of
estuarine habitat (from, e.g., contaminants, low dissolved oxygen,
etc.), current rates of estuarine habitat loss (nationwide) are now
estimated at 0.9 percent (averaging 5,540 acres annually) (Dahl 2006,
p. 16). The results of the most recent Status and Trends of Wetlands in
the Conterminous United States from 1998-2004 became available during
the status review. In summary, coastal wetlands are still being lost
but at a slower rate than in prior reports. Human-caused loss of deep
salt water in coastal Louisiana accounts for much of the recent coastal
wetland loss (Dahl 2006, p. 16). Hurricanes can also transform coastal
habitats, but the effects of this transformation of habitats on the
American eel have not been studied. A U.S. Geological Service (USGS
2006, pp. 1-2) preliminary wetland loss estimate for southeastern
Louisiana from hurricanes Katrina and Rita, which is not included in
the status and trends report, is the transformation of some 64,000
acres of marsh to open water.
From the 1950s to 1970s, substantial amounts of estuarine wetlands
were dredged and filled extensively for residential and commercial
development and for navigation (Hefner 1986 in Dahl 2006, p. 48). Since
the mid 1970s, however, many of the nation's shoreline habitats have
been protected either by State or Federal regulations or public
ownership (Dahl 2006, p. 48).
Channel dredging and overboard spoil disposal are common throughout
the Atlantic coast, and changes in salinity as a result of dredging
projects could alter the distribution of American eels. Additionally,
dredging associated with whelk and other fisheries may damage benthic
habitat for this species (ASMFC 2000, p. 42). Although it is likely
that dredging and overboard spoil disposal at least temporarily degrade
benthic habitat, we were not aware of any analysis indicating that
these activities are a threat to the American eel.
The two largest estuaries in North America are both on the eastern
seaboard and support American eels: The Chesapeake Bay and the
Albemarle-Pamlico Sound. The Chesapeake Bay and its tidal tributaries
have over 11,000 miles of shoreline; this is more than the entire West
coast. The Albemarle-Pamlico Sound, located in North Carolina, is the
second largest estuary with 1.5 million acres of brackish estuarine
waters (EPA 2006, pp. 3-4).
Although there are limitations to the following data, as they
include areas outside the range of the American eel, the status and
trends report estimated that in 2004, there were slightly more than 5.3
million acres (2.1 million hectares) of marine and estuarine wetlands
in the conterminous United States. Eighty-six percent of that total
area was vegetated wetland (Dahl 2006, p. 48).
Significant estuarine areas remain from Maine to Texas. Therefore,
this important habitat remains available to American eels, and there is
documentation of distribution of the yellow stage of American eels
within estuarine areas from commercial harvest data (Weeder and
Hammond, in press, pp. 1, 6), surveys, and research data (Helfman et
al. 1984, p. 135; Morrison et al. 2003, pp. 91-92).
Marine. New information on marine or saltwater habitat became
available during the status review (Daverat et al. 2006, see
Background, Facultative Catadromy). The relative importance of marine
habitat is not well understood, and the use of marine habitat by
American eel for growth and maturity has only been recently confirmed.
There was earlier confirmation in Japanese and European eel. We do not
know what percent of the eel population inhabits strictly marine
habitats, but eels in this habitat have high growth potential (Knights
et al. 2006, pp. 6, 10-11), there is a predominance of females, and
extensive habitat is available. Sasal et al. (2001 in Knights et al.
2006, p. 12) found the female-male ratio to be 4:1 for Japanese eel
caught in the East China Sea from 1952-1999. Knights et al. (2006, p.
13) calculates that for the European eel in England and Wales the
combined estuarine and marine contribution to reproduction probably
exceeds that of fresh water. Others have also suggested that the
percent of the American eel population living in estuarine and marine
waters, particularly those that will contribute to future generations,
may be quite high (Cairns 2006a, p. 1). Although there is no available
data on the distribution of the American eels in marine waters
throughout their range, the estimated totaled nearshore habitats (tidal
fresh areas, through mixing areas, to seawater) are substantial. In the
United States nearshore habitats have been estimated at 5,379
km2 for the North Atlantic, 20,298 km2 for the
Mid Atlantic, 12,172 km2 for the South Atlantic, and 30,604
km2 for the Gulf of Mexico (ASMFC 2000, p. 35; NOAA 2006,
pp. 1-3); this amounts to a total of 68,453 km2. No threats
to the American eel in marine habitats are known to exist.
Freshwater Habitat
Lacustrine Habitat. Lacustrine, or lake, habitat has historically
been considered among the most important habitats for eel because some
very well-known lake habitats, such as Lake Ontario, produce
exclusively large, highly fecund females (Castonguay et al. 1994a, p.
481; Casselman 2003, p. 255). Studies by Oliveira et al. (2001, pp.
947-948) showed that the greater the amount of lake habitat within a
watershed, the more the sex ratio favors females. There are numerous
lakes within the distribution of the American eel, many of which have
likely been impacted by water quality issues or exotic species
invasions, and American eels have been denied access to some historical
lake habitats due to barriers (see Riverine Habitat below for more
discussion of barrier impacts) such as dams constructed in the past. We
are not aware of new dam construction activities that are likely to
threaten the American eel. Below we will present the information on two
lakes, Lake Champlain and Lake Ontario that are in the Saint Lawrence
River drainage. It has been suggested in the literature that a cause of
declines of American eels in these lakes was barriers.
The significance of Lake Ontario's reproductive contribution to the
American eel was presented and discussed at a workshop (Casselman 2006,
pp. 1-8 in USFWS 2006, pp. 8-10) and presented in the recently released
COSEWIC Assessment and Status Report on the American Eel
[[Page 4980]]
(2006, pp. 35-41) (see Background, Population Status for further
discussion).
Access to Lake Ontario and other Great Lakes by American eel was
restricted to a degree by the building of hydroelectric facilities on
the St. Lawrence River; however, the building of canals also opened new
avenues and even provided passage past the natural barrier of Niagara
Falls. Eels migrating into the Great Lakes and Finger Lakes basin in
New York historically had one route through the Gulf of St. Lawrence
and up the St. Lawrence River to Lake Ontario. Once in Lake Ontario,
the eels could access a large number of tributaries in the United
States or Canada, but were blocked from Lake Erie and the upper Great
Lakes by the natural barrier at Niagara Falls. With the opening of the
Erie Canal in 1825, and later, the New York State Barge Canal in 1928,
a second route up the Hudson River and through the canal system was
created, allowing eels another access route to Lake Ontario and the
Finger Lakes (Patch 2006, p. 2).
Although the building of the Beauharnois Dam blocked American eels
from passing directly up the St. Lawrence River for 70 years, many eels
were able to continue their migration through the adjacent canal--the
St. Lawrence Seaway. Two ladders were recently constructed on the
Beauharnois Dam, increasing the opportunities for upstream eel passage
at that site. A second large hydroelectric dam, the Moses-Saunders Dam,
is located 40 miles upstream from the Beauharnois Dam. From 1959 until
1974, eels were able to pass upstream of the Moses-Saunders dam only
through the Wiley-Dondero Canal (Verdon and Desrochers 2003, p. 140-
141). In 1974, an eel ladder was constructed on the Canadian side of
the Moses-Saunders Dam, allowing American eels to again migrate
directly up the St. Lawrence to Lake Ontario (Casselman et al. 1997, p.
163), and a ladder on the U.S. side of the Moses-Saunders Dam was
completed in 2006. These historical and recently constructed fish
ladders are likely to benefit American eels in the SLR/LO by providing
them with multiple opportunities to access to this drainage.
Lake Champlain also produces predominately female eels. Declines in
Lake Champlain were noted in the fishery in the Richelieu River (the
river carrying about 3 percent of the fresh water from the lake to the
St. Lawrence River). The decline has been mainly related to the
rebuilding of two old cribwork dams on the Richelieu River in the 1960s
(Verdon et al. 2002, p. 2) that impeded access to Lake Champlain by
young up-migrating eels. In 1997, a ladder was retrofitted on the
Chambly Dam to enhance eel recruitment, and in 2001, the Saint-Ours
dam, downstream, was retrofitted with a similar eel ladder (Verdon et
al. 2002, p. 11-12). In 1997, the total population at the foot of the
dam was estimated at 19,650 individuals, and minimum ladder efficiency
was estimated at approximately 57 to 68 percent. Access to Lake
Champlain, having been reestablished, now allows American eel access to
1,200 km2 of habitat (Verreault et al. 2004, p. 5).
Although we are not aware of a rangewide analysis of the remaining
amount of lacustrine habitat available to the American eel, according
to the NatureServe data a significant amount of lacustrine habitat
remains available to the American eel. A survey of 203 randomly
selected lakes in eight states in the northeast United States showed
American eel as being present in at least 20 percent of the lakes
sampled (Wittier et al. 2001, p. 1).
Also, efforts are being undertaken in the two large lake systems
described above to increase American eel densities. A 10-year annual
transfer to Lake Champlain of 0.5 to 1 million elvers from the Bay of
Fundy (New Brunswick, Canada) is underway as an effort to improve
abundance within Lake Champlain (Dumont et al. 2006, pp. 1-2). In Lake
Ontario, 50,000 young eels were recently stocked as a first step in a
Canadian multi-year plan to restore the American eel to greater numbers
in Lake Ontario (CNEWS 2006, p. 1).
Riverine Habitat. Riverine habitat within the range of the American
eel is highly variable with respect to water depth, temperature, and
flow, and habitats available. Therefore, yearly reproductive
contributions vary among river systems. The amount of habitat, rather
than specific types of habitat within the river, primarily determines
how many eels a river can support (Oliveira and McCleave 2000, p. 148-
149). Both males and females are produced; densities of eels apparently
determine the sex of individual eels, rather than habitat type (see
Background, Sex Determination).
Loss of access to riverine habitat has been put forward as a threat
to the American eel (ASMFC 2000, pp. 35-39) by both decreasing
distribution and abundance. However, most of the loss of access to
riverine habitat occurred prior to 1960 and we have no information of
future water development projects that threaten the American eel. Below
we will discuss effects of the construction of dams to the eel's
distribution first. Busch et al. (1998, pp. 1-3) conducted a
preliminary analysis of stream habitat availability for diadromous fish
in Atlantic coast watersheds. They reported that from Maine to Florida,
15,115 dams have the potential to hinder or prevent upstream and
downstream movement of fish such as eels, resulting in a restriction or
loss of access to 84 percent of the stream habitat within the Atlantic
coastal historic range. This constituted a potential reduction from
345,359 miles (556,801 kilometers) to 56,393 miles (90,755 kilometers)
of stream habitat. However, only 35 percent (5,387) of the dams from
Maine to Florida are over 25 feet in height. The majority (65 percent
or 9,728) are, therefore, less than 25 feet in height. Regional
analysis of two watersheds in the South Atlantic area noted that eels
remained present over many barriers, until those barriers reached 50
feet in height (Cantrell 2006, pp. 4-5). Of the 15,115 dams, only 7
percent are for hydroelectric power (Busch et al. 1998, p. 3).
Most barriers are thought to have been in place before the 1960s.
Castonguay et al. (1994a, p. 484) reviewed major habitat modifications
as a potential cause for the extreme decline of American eels in the
Lake Ontario and Gulf of St. Lawrence ecosystems. Anthropogenic (human-
caused) habitat modifications in the Lake Ontario and St. Lawrence
River ecosystem occurred mostly before the 1960s, whereas the eel
upstream migration decline noted at the Moses-Saunders Dam started only
in the early to mid 1980s. Castonguay et al. (1994a, pp. 484, 486)
proposed that the lack of temporal correspondence between permanent
habitat modifications and the start of the regional decline evident in
the SLR/LO argues against the role of habitat loss in the decline, as
the decline should have been evident earlier than the 1980s. This
assessment was tempered by the brief mention that American eels may be
slower to respond to impacts than other fish species.
Riverine habitats within the range of the eel can be highly
degraded through contaminants (see Factor E, Contaminants) and changes
in temperature, pH, and biological communities. The effect, if any, on
eel is an increase in susceptibility in eels to disease, likely
decreased growth (Machut 2006, p. 152; USFWS 2006, p. 27), increased
elver mortality (Jessop 2000, pp. 523-524), and changes in behavior
(USFWS 2006, pp. 9-10). Stream flow velocities can affect the upstream
migration of elvers (Jessop 2000, pp. 515, 520) due to their weak
swimming ability. However, reduced velocities due to seasonal or
operational
[[Page 4981]]
changes of managed flows have likely provided periods when velocities
are passable for migration. The elver's ability to find paths around
these velocity barriers has also been documented (elvers have strong
climbing abilities and can negotiate vertical barriers) (Jessop 2000,
p. 520; Craig 2006, pp. 2-4).
Impacts of barriers on distribution: When discussing impacts of
barriers on distribution, we will cover impacts at three levels: (1)
Rivers, (2) watersheds, and (3) the American eel's entire range.
At the level of individual rivers, the impact of barriers can range
from very little impact to local or regional extirpation. This is
because the effect of barriers on eel upstream migration appears to be
site-specific. For example, a steep vertical barrier has a different
effect on elvers, which can climb, than on yellow eel, which do not
have the same climbing ability. Therefore, the location of the barrier
along the river and in the watershed will dictate its impact (USFWS
2005b, p. 16). Additionally, the level of impact is also affected by
the type of barrier (i.e., hydroelectric dam, weir, old mill dam, or
dam for recreation, water supply, or navigation), as well as how the
barrier is operated (if there is spill water), its general condition
(those in poor repair are more likely to have rough areas or spillage,
both better for eel), whether it was equipped with eel or other fish
passage, and other site specific conditions (Goodwin and Angermeier
2003, pp. 532-533; USFWS 2005b, pp. 16-19). Indeed Busch et al. (1998,
p. 3) originally suggested that site-specific assessments would be
required when further analyzing the impacts of barriers to the American
eel, and that their estimate of 84 percent loss of freshwater habitat
for the American eel was a gross estimate, provided as a starting point
for future scientific studies.
Our additional research into eel distribution shows that eels
remain widely distributed within most of the watersheds historically
inhabited by the American eel. For example, Jacobs et al. (2004, pp.
325, 330), in a Connecticut watershed survey, verifies the presence of
American eel above barriers and a current extensive distribution.
American eel were the most ubiquitous species of all fish species
sampled in the Connecticut River drainage, present in 97 percent of all
sites sampled and common in both the main stem rivers and tributary
streams (Jacobs et al. 2004, p. 325). Machut (2006, p. 49), in his
study of Hudson River tributaries, found that American eels are the
most numerous fish within the tributaries surveyed.
To better understand the impacts of historically constructed
barriers on eel upstream migration and potential loss of habitat we
analyzed three watersheds we think are representative of the U.S. range
of the species.
The Mississippi Watershed. The American eel persists in the
Mississippi watershed (Mississippi River and the tributaries of the
Missouri, Arkansas, Ohio, and Tennessee Rivers), albeit having likely
declined in abundance during the past half century (Becker 1983, p.
258). Very little data exists on the abundance of the American eel
within the Mississippi watershed (Ickes et al. 2005, p. 4), both
historically and currently, as eels are not typically targeted during
studies and are likely underestimated. The Long-Term Resource
Monitoring Program (LTRMP) conducted by the Upper Mississippi
Environmental Sciences Center (UMESC) observed 75 eels out of nearly
four million fish collected from 1993-2002 (Ickes et al. 2005, p. 9).
The distribution of the American eel remains widespread in the
Mississippi watershed even though it was anticipated by Coker (1929, p.
173) that the American eel, in time, would cease to exist in areas of
Minnesota, Wisconsin, and Iowa, due to the construction in 1913 of the
Keokuk Dam, or Lock and Dam 19, in Keokuk, Iowa (River Mile 364). The
barriers on the Mississippi River mainstem are mainly navigation locks
and dams in the upper portion of the river. These navigation locks and
dams were built to hold back water and form deeper navigation ``pools''
while allowing for barge passage through the locks. Presumably, these
lock and dam complexes allow for eel passage when barges pass (Cochran
2005, p. 2) or eels pass during high water stages, as American eel are
still found above Keokuk Dam today. The Keokuk Dam is currently the
tenth dam eel encounter during their upstream migration on the
Mississippi River.
South Atlantic-Pee Dee River and Santee River Basins, North
Carolina and South Carolina. American eels continue to be distributed
throughout the lower areas of these watersheds, indicating they are
able to negotiate certain barriers and persist within this historic
habitat. Of the six dams in the Santee and Pee Dee River basin, eels
are able to pass four (Cantrell 2006, p. 3). They are prevented from
reaching their extreme headwaters where they had historically been
reported as ``everywhere common'' by Jordan (1889, p. 139). Large (over
50 feet) hydroelectric and other dams likely impede upstream movements
of elvers and subadult eels to these historic habitats.
Androscoggin and Kennebec River Basins, Maine and New Hampshire.
Our knowledge of current distribution of American eel for the
Androscoggin and Kennebec watersheds of Maine and New Hampshire is
based on a systematic survey in 2002 and 2003, and supplemental
electrofishing survey data (Yoder et al. in preparation, pp. 1-7).
Presence of fishways on dams; dam leakage, height, configuration,
materials, and location up the river relative to the size of eel; water
quality issues; and presence of lakes (which may be of more interest to
eels due to odor cues) are thought, by Wippelhauser, to play a role in
the distribution differences within the two watersheds and explain why
eels are more abundant in the Kennebec watershed (2006a, p. 1).
The American eel remains present above the first dams encountered
inland, as well as subsequent barriers, up to the Gulf Island Dam on
the Androscoggin (approximately 52 river miles) and the Wyman Dam on
the Kennebec (approximately 122 river miles), with anecdotal
information indicating that abundance has decreased (Adams 1992, p.
86).
Rangewide our analysis of the impacts of barriers was limited to
the information available, that of North America. An update of
NatureServe's distribution map (Figure 2) includes the American eel
freshwater distribution information we received from most States within
the species' historic range as well as from Canada and a few of the
Caribbean Islands, along with NatureServe's existing database.
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At the scale analyzed, the American eel remains distributed over
roughly 75 percent of its historic native range within U.S. watersheds
(Castiglione 2006, pp. 1-5). Figure 2 represents the historic
(291,416,355 hectares) and current distribution (163,781,049 hectares)
of the American eel within its native freshwater habitat in the United
States. Additionally, Figure 2 identifies the area where the eel was
introduced and is considered currently present, an addition of
2,921,343 hectares (Castiglione 2006, pp. 1-5).
The watershed examples provided earlier are indicative of the
relationship of barriers and eel distribution throughout the species'
range in North America. From these examples, and the data from
NatureServe, we conclude that not all structures (natural or human-
made) considered barriers to other fish species should be thought of as
barriers to the eel. We also conclude that there are dams, other human-
made structures, and some natural features that are complete barriers
to American eel. In the case of human-made structures, those structures
have reduced the historical range of the American eel.
The fate of eels that are unsuccessful in passing a barrier is
unknown, but it has been speculated that eels may find alternative
habitat, that overcrowding below the barrier may increase the
likelihood the eels will become male, and that below the dams there is
likely increased competition, reduced food availability negatively
affecting growth rates, and predation (USFWS 2005b, p. 19; Machut 2006,
p. 53).
Impacts of barriers on density: Whereas general fish surveys can
provide American eel distribution data, few studies address the changes
in eel density (also called abundance) due to barriers. Goodwin and
Angermeier (2003, p. 533) found that dams can exacerbate the decline in
eel density; however, this is clearly the case for only one in three
dams within their study area. Machut (2006, p. 51) found in the Hudson
River watershed, where there are almost 800 barriers, that the first
barrier encountered dramatically reduces eel densities, but did not
necessarily result in local extirpation. Densities were highest below
barriers, while age, growth (in length), and the number of females
increased above barriers.
Two aspects of the eel's life history add complexity to
understanding the true impact that decreased density may have on eel
reproductive contribution. Densities decrease naturally with distance
from the Continental Shelf (see Background), while relative female
fecundity increases with lower density (see Background). Based on these
factors, we conclude that low upstream abundance is a natural
phenomenon exacerbated to varying degrees geographically by human-made
structures and natural barriers, but that relative reproductive
contribution is not lost in direct proportion to the decrease in
density (see Background, Distribution Clines). Additionally, we
conclude that when taking into consideration or trying to quantify the
impact of barriers on the American eel, site-specific information on
the barrier is critical, as is analyzing the historic sex ratio of an
area, the dynamic between lower abundance and the higher probability
that females will be produced, density-dependant growth relationships,
and length-fecundity relationships. Unfortunately, the information to
conduct this comprehensive analysis is not available.
The availability of riverine habitat can be seen in Figure 2, and
also be looked at in terms of kilometers of riverine habitat unimpeded.
Unimpeded freshwater habitat (riverine kilometers downstream of
terminal dams, the dams closest to the ocean) in each river also
remains available to the American eel. In the United States alone, from
Texas to Maine (not including the Great Lakes), there remains over
590,000 km of freshwater habitat available to American eels downstream
of terminal dams or within rivers that do not have significant barriers
(such as the Delaware River). An example of this downstream available
habitat on a watershed basis is the 1,153 river miles available on the
Connecticut River downstream of the terminal dam, including both the
mainstem and tributaries (Castiglione 2006, p. 1-2).
In our analysis, we found that the distribution of the American
eels has not been significantly reduced by barriers, as many barriers
do not preclude upstream migration of the American eel. Some dams
appear to form a complete barrier to upstream migration, potentially
responsible for the reduction in available freshwater habitat of
approximately 25 percent. Further, distribution is far less affected by
barriers than is density. If there were population level effects from
this decrease in American eel distribution or density in maturation
habitats, there would be corresponding declines in the recruitment of
juvenile eels; however, this is not the case (see Background,
Population Status).
Summary of Factor A
Spawning and ocean migration habitats are essential to the
persistence of the American eel; there are no apparent human-caused or
significant threats to these habitats; and, they remain available and
occupied by the American eel.
Estuarine, marine, and freshwater habitats provide maturation
habitat for the American eel, and new information verifies that some
portion of the American eel population completes its lifecycle without
ever entering fresh water. Of these maturation habitats, freshwater
habitat has been the most impacted by human-caused actions such as
barriers (i.e., dams constructed for hydroelectric, water supply, and
recreation purposes), most of which we would consider historic losses;
in which case population level impacts have likely been mostly
realized. We are not aware of future dam construction which is likely
to cause significant impact to the American eel. We have concluded that
although some dams appear to form a complete barrier to upstream
migration and likely caused the regional extirpations seen in 25
percent of the eel's historic freshwater habitat, American eels are
able to negotiate many barriers. This has allowed the American eel to
remain well-distributed throughout roughly 75 percent of its historic
freshwater range, mainly in the lower reaches of watersheds. American
eel abundance has been affected by barriers to a greater degree than
has distribution; however, there is no evidence that the reduction in
densities has resulted in a population level effect, such as a
reduction in glass eel recruitment. Analyses of local and regional
declines in abundance do not temporally correlate with the loss of
access to habitat.
The status of the American eel and the effects of freshwater
habitat loss must be examined in light of the American eel's habitation
in fresh, estuarine, and marine habitats. Highly fecund females
continue to be present in extensive areas of fresh water (lacustrine
and riverine) and estuarine and marine habitats; males also continue to
be present in these habitats. Recruitment of glass eels continues to
occur in these habitats with no evidence in reduction in glass eel
recruitment. For these reasons, we believe the available freshwater,
estuarine, and marine habitats are sufficient to sustain the American
eel population.
Factor B. Overutilization for Commercial, Recreational, Scientific, or
Educational Purposes
In analyzing the threat of overutilization, we focused primarily on
recreational and commercial fisheries on the U.S. Atlantic coast and in
Canada because these fisheries are the most
[[Page 4984]]
active. We will briefly characterize these two fisheries and discuss
recent changes, summarizing the pertinent scientific and commercial
information. For detailed descriptions of United States and Canadian
fisheries (e.g., harvest restrictions by State), see the 90-day finding
(July 6, 2005, 70 FR 38849) or ASMFC 2006a (pp. 11-20) and for Canada's
fishery, see the COSEWIC report (2006, pp. 46-48). We will begin,
however, with a short discussion of the factors that drive the
commercial harvest of Anguillid eel.
Commercial Fishery (Including Bait Fishery)
Eels (most notably Japanese and European eels) are popular seafood
in Europe and Asia, particularly Japan, and to a much lesser degree in
North America. At this time, fish culturists have not been able to
provide the conditions necessary for eels to reproduce and mature in
captivity; therefore all eels consumed or used as bait are taken from
the wild. Some of the eels taken from the wild as glass eels or elvers
are grown out to maturity in aquaculture facilities.
The commercial eel harvest both here or in other countries is
driven in large part by the international demand for eel (see Pawson et
al. 2005 for discussion of international eel market), yet American eel
represent but a fraction of the total international trade in eels.
China appears to be setting the world price by both buying eels on the
international market and producing eels in extensive aquaculture
facilities (Dekker 2005, p. 2). According to TRAFFIC, a joint program
of the World Wildlife Fund and the World Conservation Union (IUCN),
over 90 percent of the world's eel aquaculture yield takes place in the
Asian countries of Japan, Taiwan, and mainland China (TRAFFIC 2002, pp.
11-12). Between 1998 and 2004, China supplied two-thirds (i.e.,
approximately 130,000 metric tons) of the world's cultured eel
production. The species used in aquaculture in Asian countries consists
primarily of European and Japanese eel. According to the United
Nations' Food and Agriculture Organization (FAO), even with increasing
dependence on European and American glass eels for aquaculture purposes
with the decline of Japanese eels (TRAFFIC 2002, pp. 13-14), American
eels represent only about 5 percent of the overall worldwide yield of
Anguillid eels (OLE 2004, p. 1; FAO in Dekker 2005, p. 3). The
insignificant contribution to the worldwide eel trade indicates that
the American eel harvest is unlikely to be appreciably affected by
changes in international markets.
Commercial harvest of the American eel in North America occurs
mostly along the Atlantic coast of the United States and Canada. In the
United States, the commercial fishery occurs mainly in the Chesapeake
Bay with smaller fisheries scattered throughout other States. All
continental life stages are harvested commercially, but regulations
restrict harvest so that exploitation of life stages differs
geographically. American eel fisheries are unevenly distributed within
Canada. In some regions, there are intensive fisheries, while in other
regions, eels are unexploited. All continental stages are harvested
commercially in Canada, but the stages that are exploited vary
geographically (COSEWIC 2006, pp. 46-47). Limited commercial fisheries
exist in Mexico and some Caribbean islands (ASMFC 2006a, p. 14). No
glass eel or elver fishery exists in the Gulf of Mexico (ASMFC 2000, p.
18).
Exploitation rates (the percent of mortality associated with
harvest) vary with the life stage, fishing gear, and other factors.
Glass eels and elvers are typically harvested as they ascend rivers and
estuaries. One study suggests an exploitation rate of 30-50 percent of
arriving elvers (Jessop 2000, p. 523). If there was no density-
dependent change in sex ratio, growth, survival, or emigration rate in
subsequent stages, the reduction in egg production due to the elver
fishery would be equivalent to the percent elver exploitation described
above. However, such density-dependent effects are believed to occur
(ICES 2001, p. 34). In other words, the relatively high exploitation
rate for glass eels and elvers does not translate to that level of
reproduction loss because the glass eels and elvers that are not
harvested have a greater potential for survival and, therefore,
reproduction. Elver fisheries, it has been suggested by Jessop (2000,
p. 523), may be biologically justified to a greater degree in Nova
Scotian streams with low pH, given the abundance of elvers entering
these streams and the high mortalities that occur during their first
summer in fresh water (rather than in more productive streams with
higher pH values).
Silver eels are exploited in rivers mainly in weir fisheries and in
coastal waters with eel pots. In the St. Lawrence estuary silver eel
fishery, mark-recapture experiments estimated exploitation rates of 19
percent in 1996, and 24 percent in 1997 (Caron et al. 2003, p. 239).
In the Chesapeake Bay, the estimated exploitation rate is something
less than 25 percent. The data collected did not separate exploitation
rates for yellow eels harvested in the pot fishery from eels that
naturally emigrated from the area. This combined fishing mortality and
emigration was estimated at 25 percent, significantly lower than the
Prince Edward Island fishery presented below (ICES 2001, p. 34).
Data from Prince Edward Island, Canada, were used by the authors of
the ICES report (2001) to calculate yellow eel exploitation rates. They
estimated an approximately 50 percent rate of exploitation in estuary
and tidal waters (ICES 2001, p. 41). The authors also estimated how
this rate of exploitation would be expressed in loss of reproductive
contribution, but based on some significant assumptions, they consider
the estimate preliminary. They suggest the effect on reproduction would
be a decrease of approximately 90 percent, based on the premise that
the largest, and hence most fecund, females are targeted. However, they
also note that the estimated reduction in reproduction for the entire
Prince Edward Island area would be less than this value, because there
is no eel fishery in non-tidal waters, and there is minimal fishing
effort in the central and western portions of the Northumberland
Strait, which amount to about one third of the Prince Edward Island
coastline (ICES 2001, pp. 34-35).
Exploitation rates are lacking for most of the range where the
American eel is harvested, but the above examples show how complex
estimating exploitation rates is, given that factors, such as areas
unfished, need to be accounted for when evaluating harvest effects on a
species rangewide.
The American eel fishery has changed over time. Harvest, or
landings, were significantly higher in the 1970s (Figure 3), presumably
as a result of demand for glass eels for the newly emerging aquaculture
industry in China (St. Pierre 1998, p. 1), which inflated prices and
made eel fishery profitable. Landings have declined in the United
States and Canada since then; however, the reason for the decline in
landings appears multifaceted.
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The price per pound fluctuates considerably for American eel,
thereby affecting landings. For instance, the Chinese aquaculture
market still requires glass eels to maintain the established
aquaculture business (Moriarty and Dekker 1997 in ASMFC 2006a, p. 6),
but when available, the Chinese buy Japanese glass eel, which is the
eel preferred by Asians. Consequently, the price for American eel has
dropped. ASMFC (2006, p. 7, 12-13, 43) also lists poor market
conditions as likely responsible for more recent reductions in all
commercial eel fisheries. Since 1998, glass eel market prices have
fluctuated from $300 per pound (1998), to $10-$15 per pound in 1999, to
$105-300 per pound in 2005, to $60 per pound in 2006 (Wippelhauser
2006b, p. 1).
License requirements and State-regulated size and catch limits have
also played a role in the decline seen in landings (ASMFC 2006, p. 43).
In 2000, the ASMFC (the agency regulating harvest along the U.S.
Atlantic coast), responding to the concerns of fishers, scientists, and
resource managers that American eel had declined from historic levels
and that assessment data was limited, implemented a Fishery Management
Plan that required States to establish minimum size limits for
commercial eel fisheries.
Trends in Canadian eel fishery. In Canada, there has been a trend
towards increasingly restrictive fishing regulations in the last
several decades, especially in the Atlantic Provinces, and especially
since 2000 (Cairns et al. 2005 submitted in COSEWIC 2006, p. 48). This
could translate, we believe, to a decline seen in Canadian landings
data. Changes include shortening of seasons, increases of minimum size,
caps on the number of fishing gear that can be deployed, and freezes on
development of any new American eel fisheries (COSEWIC 2006, p. 48).
There was a buy-out of 50 percent of commercial licenses at Lake St.
Pierre, the fishery in the Richelieu River was closed in 1998, and the
fishery in the upper SLR/LO was closed in 2004 (OMNR 2004, p. 1). Glass
eel and elver fishery only exists in the Scotia-Fundy area of the
Maritime Provinces and occurs during narrow time windows (COSEWIC 2006,
pp. 46-47).
Trends in United States glass eel and elver eel fishery. During the
lucrative early 1970s, Florida, North Carolina, South Carolina,
Virginia, Massachusetts, and Maine developed glass eel and elver
fisheries. By 2002, all Atlantic coast States except Maine and South
Carolina had restrictions on harvestable eel size or fishing gear that
restricted glass eel and elver fishery (ASMFC 2006a, pp. 12-18). One of
those remaining States, Maine, began in 1999 to limit glass eel
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and elver harvest through emergency legislation with a limited entry
system, restrictions in fishing gear, restrictions on locations, and a
reduced length of the season (March 15-June 15). This later requirement
allows for one or more months in winter when glass/elvers are not
harvested. The emergency legislation reduced fishing effort in Maine by
at least 79 percent (ASMFC 2005, p. 18), ensuring that a significant
run remains in Maine waters. Maine was the only State reporting glass
eel and elver landings in 2004, at approximately 0.5 metric tons, down
from 7.53 metric tons in 1995, and 9.98 metric tons in 1977. South
Carolina and Florida permit glass eel fishery, but it is not active
(ASMFC 2005, pp. 5, 14).
Trends in United States yellow and silver eel fishery. Currently a
yellow and silver eel fishery exists to varying degrees in all States
and jurisdictions along the Atlantic coast except Pennsylvania and the
District of Columbia. South of Maine, the yellow and silver eel fishery
seems to be primarily coastal pot fisheries, and different States have
varying regulations, if any, imposed on this fishery. In Maine, the
yellow and silver fishery occurs in both inland and tidal waters (ASMFC
2006a, pp. 19-20). The Maine fishery has declined since 1998 because of
legislation and poor market conditions, with prices paid declining from
$3-$4 per pound to $1.25-$1.75 per pound. Harvesters report that the
low prices are due to eels being grown out in aquaculture facilities in
Canada (Knights 2003, p. 242). Eels grown out in an aquaculture
facility, a fish company representative suggests, are better suited to
smoking, due to their high fat content and uniform size and shape. The
uniform size is better suited for the current mechanized processing
(Feigenbaum 2005, p. 12). The decline in effort may encompass other
areas along the Atlantic coast as well (ASMFC 2006a, pp. 13-14). For
example, on the northern shores of New Jersey, the number of active
fishers has declined from 16 in 1980s to 0 in 2004 (Feigenbaum 2005, p.
6).
In characterizing the future impact of harvest, the literature
supports the prediction that 1970s harvest levels are unlikely to occur
again due to the changes in the market (Pawson et al. 2005, p. 6;
Dekker 2005, p. 2), including the interest in eels raised in
aquaculture facilities rather than wild caught eel, due to ease of
processing (Feigenbaum 2005, p. 12); the implementation of harvest
regulations (ASMFC 2006a, p. 43); and the retirement of eel fishers
(Wippelhauser 2006b, p. 1).
Population level impacts. In assessing population level impacts of
commercial fishing on American eels, we took into account both the
species' resiliencies and vulnerabilities, and levels of exploitation,
including a review of fished versus unfished areas in the species'
range, and whether there is evidence of a population level impact.
Resiliencies include the following: (1) The wide range of the
species, which leaves many areas without fishing pressure (USFWS 2005b,
pp. 69-70, 76; COSEWIC 2006, pp. 46-47, 53; Cairns 2006c, pp. 1-3); (2)
harvesting within an area is unlikely to substantially affect the
replenishment of the area through recruitment (to the degree it might
with fish species that have river specific stocks) because of the
random nature of recruitment (see Background section and Factor E Ocean
Conditions); (3) harvesting will not affect genetic variability because
the species is a single population; (4) eels have relatively high
fecundity rates; and (5) the species possesses general plasticity and
robustness (Knights 2005 in USFWS 2005b, pp. 50-59); also see
Background for further explanation and citations). Conversely,
vulnerabilities include the following: (1) All eel harvest takes place
before the species has had an opportunity to spawn, and American eel
only spawn once; (2) all continental life stages and multiple year
classes are subjected to harvest in some portions of the species'
range; and (3) harvest of large individuals unequally affects females
(eels below 40 cm in length are either male or female, but almost all
eels greater than 40 cm are female) (ASMFC 2000, p. 2; USFWS 2005b, p.
75).
Although we have data on landings (harvest) of American eel, we
lack specific data on fished versus unfished areas over the range of
the American eel. Recent mapping by Cairns and others (2006c, p. 3) has
begun to identify (but not yet quantify) fished versus unfished areas
in Canada, but initial results suggest that much of the Canadian range
of the American eel is unfished (COSEWIC 2006, pp. 46-47, 53). In
Canada, there is little eel fishing effort in the Gulf of Nova Scotia,
and none in most fresh waters of the southern Gulf of the St. Lawrence
River. Many rivers and coastal areas in the Scotia-Fundy area of the
Maritime Provinces are unfished and Newfoundland and Labrador have
rivers which are not exploited. Additionally, there are the areas of
harvest closure including the Richelieu River and Lake Ontario (Cairns
2006c, pp. 1-3).
Although we do not have similar mapping in the United States, there
are considerable areas within the species' range that are not subject
to harvest. Commercial eel harvest is either prohibited (such as in
Tennessee, Todd 2006, p. 1) or at low levels in States within the
Mississippi watershed (Keuler 2006, p. 1) and the U.S. portion of the
Great Lakes (Lutz 2006, p. 1). Although the ASMFC was unable to provide
fished versus unfished areas along the Atlantic coast, a fish company
representative who works with the fishers was able to confirm that
there are areas along the Atlantic coast which support eels and are not
now being exploited (Feigenbaum 2006, p. 6).
Modeling exercises have indicated that harvest has depleted the
abundance of eels in the Chesapeake Bay, where approximately 50 percent
of the U.S. yellow eel landings occur (Weeder and Uphoff, in press, pp.
6-7). Modeling conducted by BEAK (2001, pp. 31, 5.1, 5.7) for the
purposes of prioritizing factors influencing eel abundance, ranked
fishing mortality on yellow and silver eels as the number one factor
with regards to American eel abundance in the upper SLR/LO. The upper
SLR/LO was an area of substantial harvest beginning in the 1970's, with
a peak in 1978 of 230 metric tons (Robitaille et al. 2003, p. 258).
Commercial harvest in the upper SLR/LO closed in 2004.
At a population level, however, one must take into account existing
regulations and exploitation rates that allow for: (1) A level of
individuals who are not subjected to fishing pressure; (2) the theory
that fishing of glass eels and elvers does not necessarily represent a
substantial loss to reproductive capacity of the species; (3) the vast
areas that remain unfished; and, (4) the lack of evidence that there is
a reduction in glass and elver recruitment rangewide (which would be
the indicator of overharvest) (see Background, Population Status).
Taking all these factors into account, we have determined that
commercial harvest currently affects the American eel only at a local
or regional level.
Recreational Fishery
Recreational harvest is either limited or nonexistent throughout
most of the range of American eel. Eels are likely purchased or caught
by recreational fishermen for use as bait for larger gamefish such as
striped bass (USFWS 2005b, p. 74; ASMFC 2005, p. 6), and the remainder
is mostly catch and release (ASMFC 2005, pp. 5-6). The NMFS Marine
Recreational Fisheries Statistics Survey (MRFSS), which has surveyed
recreational catch in ocean and coastal waters since 1981, shows a
declining trend in the recreational catch of eels during the latter
part of the
[[Page 4987]]
1990s. In 2003, total recreational catch was 156,381 eels, and in 2004,
112,001 eels. In 2004, the combined catch from New Jersey and Delaware
represented 40 percent of the recreational American eel catch, and the
combined catch from New York and Delaware represented 62 percent of the
recreational American eel harvest. About 79 percent of the eels caught
were released alive by the anglers in 2004 (ASMFC 2005, p. 6).
To protect American eel from unregulated recreational harvest, all
ASMFC member States were required to establish uniform size (6 inches)
and possession limits (maximum 50 eels per person per day) for
recreational fisheries, and recreational fishermen are not permitted to
sell eels without a State license that specifically authorizes this
activity (ASMFC 2006a, p. 17). After a review of the best available
scientific and commercial information, it does not appear that
recreational harvest poses a significant threat to American eel.
There is little information in the literature on subsistence
harvest and bycatch. But according to Laney (2006, p. 1) and others
(USFWS 2005b, p. 14, 79), bycatch of eels in marine waters, during
harvest for other targeted fish species, does not appear to be of
concern for the American eel. This is likely due to the fishing gear
used in these other fisheries (Laney 2006, p. 1). Fisheries utilizing
trawl gear may catch eels, depending on the size of the netting.
Netting of a \1/2\ inch and 1 inch used in the late 1960s did catch
eel, but only a handful (Wenner 1973, p. 1). Modern netting size is
more specific to the targeted fish species in an attempt to limit
bycatch.
Summary of Factor B
In conclusion, there are no data to suggest that subsistence
harvest, bycatch, and recreational harvest are having a significant
impact on American eel regionally or rangewide. Future commercial
harvest of American eel is not anticipated to reach 1970s levels, and
we find it unlikely that American eel landings will increase
significantly by future changes in the international market.
Commercial harvest has had a strong influence on eel densities in
some local and regional areas, but we see no evidence that commercial
harvest is having an effect at a population level. A population level
impact would be seen in declines in juvenile recruitment rangewide, yet
this is not in evidence. It is probable that: (1) The random dispersal
of the larval stage enables the species to successfully recruit to
other areas, including extensive unfished areas, throughout its range,
thereby buffering the effects of harvest; (2) the compensatory
mechanism of the increasing probability of glass eel and elver
survival, or of undifferentiated eels becoming female, as densities
decrease provide this species with some level of resilience; and, (3)
current exploitation rates and regulations insure that substantial
numbers of eels remain unfished. These factors are likely sufficient
enough to maintain the species as a whole even under foreseeable
fishing pressure. As such, we have determined that harvest is not a
significant threat to the American eel at a population level.
Factor C. Disease or Predation
In our analysis of diseases and predation, we focused on the
diseases and types of predation that were most likely to affect the
American eel at a population level.
Predation
We evaluated changes in predation as a result of human-caused
activities. It had been suggested in the 90-day finding that American
eels blocked or delayed at upstream barriers could experience higher
than normal mortality rates due to predation, because birds of prey and
piscivorous fish often congregate at the base of dams to prey on other
fish species (USFWS 2005b, p. 20). However, we found nothing more than
anecdotal information on this topic, and therefore we were unable to
quantify the impact of predation as a result of barriers. Natural
predation rates are likely very high for elvers upon entering
freshwater (see Background, Juvenille Mortaltiy and Jessop 2000, p.
522), but there is no evidence to indicate that natural rates of
predation have risen, or that eel population numbers are approaching a
diminished level where natural predation rates pose an increased risk
to the eel rangewide (USFWS 2005b and 2006).
Disease
We analyzed whether the spread of fish diseases, and in particular
parasites, has accelerated due to human activities, including global
transport of fish for aquaculture, and whether the threat of disease
presented a risk to the American eel at a population level.
Parasites. The parasite of most concern is the nonindigenous
nematode Anguillicolla crassus, a parasite with five life stages that
becomes sexually mature in the swimbladder of the eel. The only other
parasite found in the eel swimbladder is another nematode, Daniconema
anguillae (Moravec and K[oslash]ie 1987 in Kirk 2003, p. 387), but it
rarely occurs in high numbers (Kirk, unpublished observations in Kirk
2003, p. 387).
Although there is no direct evidence that A. crassus prevents
Anguilled eels from completing their spawning migration or influencing
the silvering process, hypotheses, such as those of Kirk 2003, have
suggested that A. crassus may impair the capacity of the eel to
undertake the migration to the Sargasso Sea. Presented below is the
history of invasion by A. crassus, percentage of American eels
infected, the known physiological effects on Anguilled eels from A.
crassus, hypotheses regarding impacts to outmigrating silver eels, and
our analysis of the data.
Native to Japanese eel, A. crassus invaded wild populations in
Europe, most likely through aquaculture, around 1982, and in North
America (Texas) about 1995, again likely a result of transported eels.
Since then, the U.S. invasion by A. crassus has spread north along the
Atlantic coast. By 1997, 10 to 29 percent of the American eels in the
Chesapeake Bay were infected by A. crassus, and by the year 2000,
greater than 60 percent of the American eels in the freshwater portions
of the Hudson River, New York, were infected. The known northern extent
of the parasite at this time is the Sedgeunkedunk Stream in Maine
(USFWS 2006, p. 2). Although it has not yet been detected in Canadian
waters, it is believed that A. crassus is likely to spread to Canada in
the future, potentially through aquaculture, because there do not
appear to be limiting factors for the parasite spreading farther north
(USFWS 2006, p. 2, 7). Temperature is apparently not a limiting factor
(although temperatures at or below 4 [deg]C slow infection rates), nor
is salinity (although rates of infection have been shown to be lower in
brackish waters), and the parasite has now been found in all size
classes of eel (Oliviera 2006, pp. 1-20, in USFWS 2006, p. 2).
An aspect that may aid in the spread of the parasite is the number
and variety of intermediate hosts (currently 12 families, both fish and
invertebrates, are known to serve as intermediate hosts). However,
physical barriers, such as dams and natural waterfalls, which likely
preclude movement of intermediate hosts, have been shown to
significantly reduce infections of eels upstream beyond the second
barrier (Machut 2006, pp. 75, 81-82). Also the expulsion of ballast
waters may be providing transport for the parasite. Recent research
indicates rivers with large ports have the highest rates of infection,
leading researchers to the conclusion that ballast water may
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explain continued invasion (Oliveira 2006, p. 19 in USFWS 2006, p. 2).
Another recent finding is that urbanization may increase susceptibility
to infection. Elevated infection rates were present when urbanized
lands exceeded 15 percent (Machut 2006, p. 82).
The percentage of American eels infected by A. crassus can vary
significantly. In one North Carolina study the percentage of American
eels infected ranged from 10 to 100 percent, between sites studied
(Moser et al. 2001, p. 1). Hypotheses suggested to explain this wide
range in American eel infection rates include: (1) Eels occurring near
large shipping ports will have more exposure to exotic parasites,
possibly as a result of infected intermediate hosts being transported
by ballast water; (2) warmer waters are equated with higher prevalence
of parasitic infection; and, (3) the longer a watershed has been
infected, the higher the anticipated infection rate (USFWS 2006, p. 1-
8).
Although A. crassus infection causes physiological damage to the
swimbladder, this damage is not much of a concern except for silver
eels during outmigration. There is no apparent detrimental effect on
eel weight and length in the yellow eel stage, but the demands on the
swimbladder, which assists in buoyancy and depth control, would be
greatest during outmigration because the eel may use deeper waters on
its trip back to the Sargasso Sea to spawn. The parasite typically
lives for several months and therefore likely persists during
outmigration (van den Thillart et al. 2005, pp. 7, 233; USFWS 2006, p.
2). According to Knopf and Mahnke (2004, p. 494), Japanese eel are not
affected by A. crassus to the degree that a non-adapted host, such as
the European eel (and presumably American eel) is because the Japanese
eel possesses more effective defense mechanisms against A. crassus,
likely due to the co-evolution process which resulted in a balanced
host-parasite system without significant harm to the host. Kirk (2003,
pp. 390, 391) presents studies suggesting there may be a level of
immunity that develops in the non-adapted hosts.
Laboratory studies in the European eel, have shown that light
(approximately 5 nematodes per eel) and moderate infections can reduce
eels' swim capacity, perhaps by as much as 10 percent (Sprengel and
Luchtenberg 1991 in Moser et al., 2001, p. 851). W[uuml]rtz et al.
(1996 in Kirk 2003, p. 390) demonstrated that adult parasite
intensities of greater than 10 adult parasites per eel can reduce the
proportion of oxygen in the swimbladder of adult eels by approximately
60 percent when compared to uninfected eels. Simulated swimming
experiments in European eel indicate the impact of heavily parasitized
eels (20 or more parasites) results in a decrease in swim efficiency
and possibly reduced buoyancy. Heavily infected eels were not able to
swim longer than a few months. Parasites cause the swimbladder to
shrink, resulting in higher costs of transport (van den Thillart et al.
2005, p. 105). In addition, heavy infection causes deterioration of the
swimbladder function due to severe permanent damage.
According to van den Thillart et al. (2005, pp. 233, 236) a damaged
swimbladder interferes with the buoyancy control, resulting in poor or
absent vertical navigation capacity in the open ocean and a decrease in
swim efficiency which, they hypothesize, prevents the completion of the
spawning migration. The likely result is death en route to the spawning
grounds in the Sargasso Sea.
There is a significant level of speculation about the impact of A.
crassus on the American eel during outmigration and spawning, neither
of which can be easily studied under natural conditions. A level of
uncertainty is therefore, inherent in our analysis. Also unknown is
whether contaminants may act synergistically with parasites, possibly
magnifying the impact on the species (USFWS 2006, pp. 7, 26).
For the American eel, the number of nematodes per infected eel
(mean intensities) is an important aspect in evaluating the potential
impact of this nematode on American eel, as is understanding the depths
at which American eels outmigrate back to the Sargasso Sea, the length
of that migration, and further understanding of what proportion of the
American eel completes its life cycle in salt and brackish water where
infection rates may be significantly lower. Unfortunately much of this
information is not available.
Mean intensities in American eels have been found to be
significantly different among sites, including being significantly
lower in brackish water when compared to fresh water, (Morrison and
Secor 2003, p. 1492). The majority of studies of American eels have
shown fairly moderate levels of intensity of infection. North Carolina
had a mean ranging from 2.0 to 12.3 nematodes per eel, depending on the
river (Moser et al. 2001, p. 851). Mean intensities of infection of
eels from the Hudson River in early studies were 1.0 to 1.7, increasing
over time to 3.2 and 23.7, depending on the site (Morrison and Secor
2003, p. 1491). Low to moderate mean intensities of 2.6 to 9.0 were
reported in the Chesapeake Bay (Barse et al. 2001, p. 1366). It is
unknown if these relatively moderate mean intensities would have the
same impact on American eels under natural conditions as was reported
by the recent laboratory research by van den Thillart et al. (2005, p.
105) on European eels where higher densities of parasites caused a
decrease of the optimal swim speed and increased the energetic cost of
swimming.
We remain cautious in extrapolation of these preliminary laboratory
studies with regard to rangewide implications given the absence of
evidence for population-level effects, such as reduced recruitment of
glass eels (which would be an indicator of decreased outmigration
survival). This being said, we acknowledge the statement by the
International Council for the Exploration of the Sea (ICES 2001, p. 6)
that due to the fairly recent invasion of the U.S. by A. crassus and
the long-lived nature of at least a portion of the American eel
population, the impact of A. crassus on American eel may not yet have
been fully realized. ICES (2001, p. 6) concluded that, for the European
eel, the occurrence of this parasite does not match the timeline for
when the decline in recruitment for European eel occurred. Given the
extensive research on the European eel and the reasons for its apparent
decline this statement should be given due consideration.
In summary, indigenous parasites are not known to be of significant
concern to American eel at a population level. During the status
review, we were provided with new information on the nonindigenous
parasite A. crassus, including the northern extent of invasion. The
literature details the impacts to individual European eels by A.
crassus in a laboratory setting, and puts forward the hypothesis that
these impacts reduce an individual's chance of successful spawning.
However, similar research in the American eels has yet to be undertaken
and several factors pertaining to the American eel may indicate less
potential impact from A. crassus: (1) The mean intensities reported for
American eels appear to be moderate; (2) the American eel has a shorter
outmigration distance to the Sargasso Sea than European eels; (3) some
areas currently are free from A. crassus infection (Canada, and
possibly Central and South American and the Caribbean Islands); and (4)
areas remain where A. crassus is found, that are still
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producing uninfected outmigrating individuals.
Pathogens. Viruses such as EVA (Eel Virus--America) and bacteria
are present in the American eel, and periods of stress, such as
metamorphosis, may activate viruses and bacteria. Although mortality
from viruses may occur, there is no information available about virus
prevalence and impact on American eel at a population level.
Van den Thillart et al. (2005, p. 7) found that European eels
infected with the rhabdovirus EVEX (Eel Virus European X), a virus
widely spread in the European eel population, developed hemorrhage and
anemia during simulated migration in large swim tunnels and died after
swimming for 1,000 to 1,500 km (estimated European eel outmigration to
the Sargasso Sea is 5,500 km). The resting group of eels did not
develop the disease, although they were also infected with the virus.
This supports the theory that stress, such as completing metamorphosis
and migrating, may activate the virus. Because none of the infected
swimming eels survived the swim test, the authors concluded that virus
infections may adversely affect the spawning migration of eels. The
virus infection appeared more severe than the infection with the
swimbladder parasite, A. crassus (van den Thillart et al. 2005, p. 7).
In a report on the presence of viruses in eel populations from various
geographic regions and countries, the samples taken from the United
States (Virginia) and Canada (St. Lawrence River) were negative for
EVEX virus (van Ginneken et al. 2004, p. 270). Disease screening for
glass eels used in recent stocking programs have also been free of EVEX
virus. Other pathogens, such as Aeromonas salmonicida, a bacterium
known to cause furunculous lesions, exist in cultured American eel
(Hayasaka and Sullivan 1981, p. 658), but neither rates of infection in
the wild nor population level impacts have been established.
In summary, pathogens such as EVEX virus appear to have a
significant impact on eels in a laboratory setting; however, the
prevalence of this virus, or any other virus or bacteria, in the
American eel population is not documented.
Summary of Factor C
We conclude that predation is not a threat to the American eel at
the population level, nor are disease and pathogens. We acknowledge
that there is a high level of uncertainty with regards to the impacts
on individual silver American eels infested with A. crassus during
outmigration. However, given the absence of information for population-
level effects, such as reduced recruitment of glass eels, and given
that there remain uninfected eels for spawning and extensive areas of
the species range which are not currently invaded by A. crassus or
infection levels are low to moderate, we have determined that the
current information does not indicate that A. crassus is a threat to
the American eel at a population level.
Because outmigration occurs in the open ocean, direct study of the
effect of A. crassus under natural conditions will continue to be
difficult. This emphasizes the need for data collection and analysis
designed to differentiate between population fluctuations responding to
natural phenomena, such as oceanic conditions, and those that are
human-caused. We support the continuation and expansion of the
coastwide monitoring program started several years ago, and the ongoing
research being conducted by the scientific community.
Factor D. Inadequacy of Existing Regulatory Mechanisms
Under this factor we will briefly describe and address whether
existing regulatory mechanisms are adequate or inadequate to conclude
that the American eel is not endangered or threatened. As part of our
analysis of threats under Factors A, B, and E, we describe how certain
existing regulatory mechanisms directly or indirectly reduce these
threats (we are unaware of regulatory mechanisms that would directly
reduce the threats discussed in factor C). Based on this analysis, we
conclude that Sargassum harvest, freshwater and estuarine benthic
habitat destruction, streamflow alteration, harvest, passage barriers,
turbines, and contaminants are not significant threats to the American
eel at the population level and that additional protection is not
necessary to determine that listing the species is not warranted.
Because we found no threat that, individually or in combination with
other threats, is significant at a population level, there is no
instance in which the protections provided by existing regulatory
mechanisms are inadequate such that listing as endangered or threatened
would be necessary.
Seaweed Harvest
The status of the American eel with regard to Sargassum harvest is
influenced by the effect of the following regulation, and therefore, we
describe in this section how the existing regulatory mechanisms
directly or indirectly reduces this threat. During the status review,
we evaluated the harvest restrictions outlined in the second revised
Fishery Management Plan for Pelagic Sargassum Habitat of the South
Atlantic Region. The specified maximum and optimum harvest of Sargassum
severely limit Sargassum harvest, and American eel larvae have not been
found in the Sargassum. We concluded during the status review that the
commercial harvest of Sargassum is not a threat to the American eel
(see Factor A), and therefore we find that the regulations governing
Sargassum harvest are more than adequate for the protection of American
eel larvae.
Habitat Degradation
The status of the American eel with regard to habitat degradation
is influenced by the effect of the following regulations, and
therefore, we describe in this section how certain existing regulatory
mechanisms directly or indirectly reduce this threat.
Stream Flow and Benthic Habitat. During the status review, we
evaluated Federal and State and local regulations that afford levels of
protection and regulate benthic habitat destruction and stream flow
alteration. The Clean Water Act (33 U.S.C. 1251 et seq.) is the primary
Federal law, enacted at Federal and State levels that restricts the
degradation of benthic habitats and flow alteration. The Fish and
Wildlife Coordination Act, as amended (16 U.S.C. 661 et seq.), has been
the principal authority for incorporating fish and wildlife
conservation measures into water development projects. The River and
Harbors Act of 1938 (Pub. L. 75-685) provided for wildlife conservation
to be given ``due regard'' in planning Federal water resources
projects. The Federal Power Act, as amended (16 U.S.C. 791a et seq.),
contains requirements to incorporate fish and wildlife concerns into
licensing, relicensing, and exemption procedures. The original Federal
Power Act provides for cooperation between the Federal Energy
Regulation Commission (FERC) and other Federal agencies, including
resource agencies, in licensing and relicensing power projects.
Many States have specific laws and regulations that limit benthic
habitat destruction and flow alterations. Some mirror or implement
Federal clean water law regarding water quality standards, including
designated uses, criteria, and an antidegradation policy, which can
provide a sound legal basis for protecting wetland resources, including
benthic habitats for American eels, through State water quality
management programs. In most of the
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eastern United States and Canada, the riparian doctrine provides some
protection for maintenance of instream flows. The riparian doctrine
generally affords some protection for off-stream uses of water, while
flow alterations usually must conform to some minimum standard.
Estuarine habitat. Laws, such as the Estuary Protection Act (16
U.S.C. 1221 et seq.), the Estuaries and Clean Waters Act of 2000 (33
U.S.C. 2901 et seq.), and the Coastal Barrier Resources Act (16 U.S.C.
3501 et seq.), provide financial incentives for estuary habitat
protection and restoration. Additionally, the Rivers and Harbors and
the Federal Power Act described above would also address impacts within
estuarine waters.
During the status review, we concluded that habitat degradation is
not a significant threat to the American eel (see Factor A) and
therefore we find that the regulations governing activities such as
estuarine and benthic habitat degradation and stream flow alteration
are adequate for the protection of American eel.
Contaminants
In general, before the 1960s there were no Federal environmental
laws regulating pollution. Concerns began to mount with regard to the
threat of pollution to environmental resources and were first addressed
in 1965 with the Solid Waste Disposal Act and the Water Resources
Planning Act. In 1970 the U.S. Environmental Protection Agency (US EPA)
was established to ``protect human health and safeguard the natural
environment''. Currently there are numerous International, Federal, and
State regulations that reduce the threats of contaminants to
environmental resources such as the American eel. The 1972 Great Lakes
Water Quality Agreement was signed between the U.S. and Canada to
``restore and maintain the chemical, physical, and biological integrity
of the waters of the Great Lakes Basin Ecosystem''. In addition, Canada
also has authority to manage water resources and control pollution
under two primary acts, the Ontario Water Resources Act and the
Environmental Protection Act. Federal regulations that address
environmental contaminants include the Water Pollution Control Act and
the Federal Insecticide, Fungicide and Rodenticide Act of 1972, Safe
Drinking Water Act of 1974, Resource Conservation and Recovery Act of
1976, Clean Water Act and the Soil and Water Resources Conservation Act
of 1977, Comprehensive Environmental Response Compensation and
Liability Act of 1980, and the Oil Pollution Act of 1990. Under the
Clean Water Act, the U.S. EPA can delegate many of the permitting and
regulatory aspects of the law to state governments. In accordance with
the Clean Water Act and state statutory authority, individual states
have developed water quality regulations that are comparable to and
often more stringent than the Federal regulations.
We concluded during the status review that contaminants are not a
significant threat to the American eel (see Factor E), and therefore we
find that the regulations governing contaminants are adequate for the
protection of the American eel.
Fish Passage
The status of the American eel with regard to barriers and turbines
are influenced by the effect of the following regulations, and
therefore, we describe in this section how certain existing regulatory
mechanisms directly or indirectly reduce these threats.
During the status review, we evaluated section 18 of the Federal
Power Act (16 U.S.C. 791a et seq.). Section 18 is the regulatory
mechanism that specifically provides for fish passage prescriptions by
the Secretary of Interior (as exercised by the USFWS) and the Secretary
of Commerce (as exercised by NMFS) for dams regulated by FERC. Most
States within the range of the American eel in the United States have
specific fish passage laws, and those State resource agencies often
work closely with the USFWS or NMFS when creating fish passage
facilities. Sometimes fish passage is incorporated in the 401 Water
Quality Certificate issued by the States under the Clean Water Act (33
U.S.C 1251 et seq.).
Along the Atlantic coast, most fish passage facilities are
prescribed under section 18 of the Federal Power Act or recommended
under section 10(j) of the Federal Power Act administered through FERC
at hydroelectric facilities. On the mainstem of the upper Mississippi
River /Illinois Waterway, the Army Corp of Engineers (ACOE) owns and
operates a series of navigation locks and dams for the Federal 9-Foot
Channel Project. However, other than recommendations made by resource
agencies under provisions of the Fish and Wildlife Coordination Act (16
U.S.C. 661 et seq.), there is no specific regulatory mechanism
requiring the ACOE to provide fish passage (Wege 2006, p. 6). There may
be opportunities in the future for fish passage under the proposed
Federal Navigation and Ecological Sustainability Program, which
requires Congressional authorization and funding. Many of the large
reservoirs in the Midwest were constructed by the ACOE and remain under
its jurisdiction. In the Tennessee River Valley, the Tennessee Valley
Authority owns and operates 49 developments for flood control,
navigation, and hydroelectric development; none of these facilities is
operated specifically for fish passage, although some upstream and
downstream passage is likely through those mainstem dams with locks
(Wege 2006, pp. 5-6). Recent records of American eels from the
Tennessee and Cumberland River are few (Etnier and Starnes 1993, p.
120).
Thousands of small dams that were constructed over the last several
hundred years for water power to run grist mills, saw mills, and
textile mills, as well as for water storage for drinking water and
other industrial and municipal purposes, are exempted from most modern
regulatory mechanisms except for State dam safety codes. Thousands of
dams in the Mississippi River watershed and along the Atlantic coast
fall under this category. However, as these structures age, funding is
often not available to bring them up to State dam safety codes, which
provides an opportunity for their removal (Wege 2006, p. 5).
The Energy Policy Act of 2005 (Pub. L. 109-58) amended the Federal
Power Act amended section 18 of the Federal Power Act and calls for
administrative hearings when the material facts of an agency-prescribed
fishway measure can be challenged by the dam owner or other party to
the proceeding. The alternative fishway measure presented by the dam
owner or other party can be adopted if it is as effective in purpose
and economically beneficial to the dam owner. The burden of proof, of
both the benefit and need for the fish passage, has been somewhat
shifted from the private sector (i.e., dam owner) to the public sector
(i.e., agency personnel). Additionally, the agency is now to consider
the economic impact of a fishway prescription to the dam owner. While
the process to consider alternative fishways is new, the agencies
(USFWS and NMFS) have received and considered alternatives from license
parties as a regular practice, and have revised preliminary conditions
and prescriptions as new information was received (Hoar 2006, p. 2; DOI
2005, p. 69808). It is yet to be seen whether these amendments to the
Federal Power Act will have an effect on eel passage implementation.
In Canada, there is no licensing or regulatory system comparable to
FERC for hydroelectric dams. Canadian resource agencies must rely on
various
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fisheries laws that can be invoked, and they must often negotiate the
construction of fishway facilities rather than require them.
We have concluded that barriers limit, and in some watersheds
eliminate, access to inland portions of the American eel's range in
North America, but that there is no indication that the roughly 25
percent restriction of access to historic freshwater areas is
significantly impacting the American eel at a population level (see
Factor A). We have also concluded that turbines can cause regional
impacts to abundance of American eels within the watershed, but there
is no evidence that turbines are affecting the species at a population
level (for full discussion of turbine impacts see Factor E). Therefore
we find that the regulations governing fish passage are adequate for
the protection of American eel.
Harvest and Trade
The status of the American eel with regard to harvest and trade are
influenced by the effect of the following regulations, and therefore,
we describe in this section how certain existing regulatory mechanisms
directly or indirectly reduce these threats.
During the status review, we reexamined the ASMFC's mechanism for
regulating the commercial and recreational harvest of American eel
along the Atlantic coast States (see Factor B. Overutilization) and
ASMFC's flexibility in responding to changing stock status. The
American Eel Fisheries Management Plan (FMP) requires that member
States establish uniform size limits and other regulations for
commercial harvest. In 2005 and 2006, the ASMFC underwent a public
process for potential changes to the FMP. In 2006, the ASMFC adopted
Addendum I to their American Eel FMP (ASMFC 2006c, p. 1; ASMFC 2006d,
pp. 1-3) which requires a reporting system. Addendum 1 recommends the
implementation of a specific eel harvester permit or license for each
State. Under this addendum, each license requires reporting of trip-
level catch and effort, or States can choose to implement an eel dealer
permit and reporting system. The American Eel Technical Committee under
the ASMFC stated that this improved monitoring system will assist in
future stock assessments. The permit or license should be required for
all eel harvesters, including those who harvest eels for use as bait.
The American Eel Technical Committee also recommended a specific eel
report from dealers and a license or permit for dealers, including bait
dealers. Harvester and dealer reports must differentiate between the
amount of eels used or sold for food and the amount of eels used or
sold for bait. The Addendum responds to concerns regarding the lack of
accurate catch and effort data, and the critical need for these data
for stock assessment purposes (ASMFC 2006a, p. 2). Although silver eel
fishery and seasonal closures were options presented during the public
process (ASMFC 2004b, p. 7), no further harvest restrictions, other
than those already laid out in the ASMFC's FMP in 2000, have been
implemented at this time.
In Canada, harvest restrictions are under the purview of the
federal government unless the authority has been passed to the
Provinces. Restrictions and closures are already in effect for certain
areas in response to the decline in the upper SLR/LO (see Factor B.
Overutilization). Provincial management programs in Ontario and Quebec
have imposed license and season restrictions, and reduced quotas, in
some cases to zero catch (Mathers and Stewart 2005, p. 1). The federal
government of Canada retains authority within the Maritime Provinces.
New information was gained on the lack of restrictions in harvest
from responding countries outside U.S. and Canadian waters, and the
lack of import restrictions in the responding European countries (see
Factor B). Our determination, based on the analysis of commercial
harvest during the status review, is that although abundance of eels is
likely affected locally and regionally by commercial harvest,
commercial harvest is not a significant threat to the American eel (see
Factor B).
To protect American eel from unregulated recreational harvest, all
ASMFC member States were required to establish uniform size (6 inches)
and possession limits (maximum 50 eels per person per day) for
recreational fisheries, and recreational fishermen are not permitted to
sell eels without a State license that specifically authorizes this
activity (ASMFC 2006a, p. 17). During the status review recreational
harvest was determined not to be a significant threat to the American
eel at a population level (see Factor B).
In summary, because we conclude that Sargassum harvest is not a
threat to the American eel, and habitat degradation, harvest, and fish
passage, including turbines, were not significant threats to the
American eel at the population level, it is reasonable to conclude that
current regulatory mechanisms governing habitat degradation, harvest
and fish passage, including turbines, are adequate to the extent that
listing under the Act is not necessary.
Factor E. Other Natural or Manmade Factors Affecting the Species'
Continued Existence
Hydropower Turbines
During the status review, we examined the extensive body of
literature on the impacts of turbines to eels. Specifically, we looked
at: (1) Types of turbine impacts; (2) variations in mortality and
injury rates and possible causes; (3) uncertainties and information
gaps; and, (4) impacts of turbines on the American eel at a population
level.
During outmigration, as eels swim downriver, where hydroelectric
facilities are present, some eels become entrained and enter the
turbines. Of the eels that enter the turbines, some survive and others
are injured or die (EPRI 2001, p. 3-1). Smaller turbines and turbines
that rotate faster pose the greatest threat to eels. The degree of
injury and mortality increases with larger eels (EPRI 2001, p. 3-8),
suggesting that mortality rates of large female eels may be
disproportionately higher than mortality rates of males. Turbine
mortality to eels has also been shown to be affected by dam size,
turbine type, load, and specific operating conditions (including
nighttime versus daytime operation, because eels tend to outmigrate
during the night; peak versus off peak power production, and level of
spill), and the behavior of the eels (EPRI 2001, pp. 3-4--3-10; USFWS
2005b, pp. 30-33). There is only limited data on sublethal effects to
eels and their impact on outmigration and reproductive viability of the
population. Sublethal effects include injuries that may result in loss
of fitness (USFWS 2005b, pp. 34-36), increased risk of predation, and
delayed migration (as observed in Anguillid species native to New
Zealand) (Watene et al. 2002 in EPRI 2001, pp. 2-18).
The Electric Power Research Institute report compiled data on eel
mortality through turbines and found that not all, but most, eels go
through turbines due to migration behavior. For eels that go through
the turbines, the mortality level was highly variable, depending on
turbine design, size of eels, and operational conditions. For example,
for survival rates estimated at Moses--Saunders and Beauharnois
hydropower facilities on the St. Lawrence River, Francis turbines were
found to result in mortality rates of approximately 15 percent (85
percent survival), and fixed-blade propeller turbines were found to
result in mortality rates of
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approximately 25 percent (75 percent survival) (COSEWIC 2006, pp. 45-
46; see EPRI 2001, pp. 3-1--3-11 for more details on the impacts to
eels from turbines). Higher mortality rates have also been reported.
Mont[ecirc]n (1985 in McCleave 2001b, p. 593) reviewed literature
through the early 1970s on injury and mortality on European eel during
turbine passage. He reported injury rates, where injury likely resulted
in death, of 40 to 100 percent in 73-cm eels passing through Kaplan
turbines under various operating conditions. According to Hadderingh
(1990 in ASMFC 2000, p. 40) and McCleave (2001b, p. 611), if American
eels have to pass through turbines in their downstream migration,
mortality rates range from 5 to 60 percent.
Cumulative mortality refers to the estimated combined mortality
within a watershed, and is thought to cause significant reductions in
that watersheds' eel reproductive contribution to the population.
Verreault and Dumont (2003, p. 247) estimated combined mortality rates
of 40 percent for Lake Ontario s outmigrating female eels from the
Moses--Saunders and Beauharnois hydroelectric facilities on the St.
Lawrence River. The cumulative impact of multiple hydroelectric
projects within a watershed, as simulated by McCleave (2001b, p. 602),
indicates substantial decrease in overall eel reproductive contribution
from a watershed, even when survival rates of eel passage were high
through each successive turbine or dam project. The simulated
cumulative mortality within the watershed was approximately 60 percent
(40 percent survival) of overall reproductive contribution when
mortality per dam was 20 percent (80 percent survival). McCleave
states, however, that his model is meant as a tool to compare results
based on different inputs, not a definitive statement about cumulative
mortality within the watershed. Based on the data available, we can
reasonably assume that where American eels encounter one hydropower
facility during outmigration, there is a typical mortality rate in the
range of 25 to 50 percent, and when one or more turbines are
encountered, the range of mortality rate increases to 40 to 60 percent
for that watershed. This still leaves escapement values (the percent of
individuals who survive to continue outmigration) of a minimum of 40
percent and a maximum of 75 percent. Even if the mortality rate has
been underestimated, there are still eels in freshwater areas that are
unaffected by turbines, and eels that survive passage in spillover.
We have updated Busch et al.'s (1998) data on the percentage of
dams with turbines on the Atlantic coast and have added the Gulf Coast.
Out of the 33,663 dams, 1,511 (or 4.5 percent) are for hydropower and,
we assume, are fitted with turbines. Of these only a small percentage
(2.06 percent) are on terminal dams (Castiglione 2006, p. 1). Terminal
dams (dams closest to the ocean) fitted with turbines affect American
eels throughout the watershed as they outmigrate, but dams fitted with
turbines farther up in the watershed impact only eels outmigrating from
tributaries and the mainstem of the river above the dam, not
outmigrating eels from tributaries or mainstem river habitats below the
dam. Mapping also showed that hydroelectric facilities appear clustered
in the Northeast and Great Lakes area (Castiglione 2006, p. 2). Still,
we do not have the percent of eels subject to turbines. This number
could be relatively small given that: (1) The species' range is
extensive (see Background, Range); (2) not all Atlantic coast
watersheds have multiple hydroelectric turbines (USFWS 2005b, p. 31);
(3) dams that have turbines are likely large dams (more then 50 feet
high), which often limit upstream passage of eels in these watersheds
because of their height, and therefore limit the risk of turbine
mortality or injury at maturity (see Factor A); and, (4) there are
tributaries to the Gulf of Mexico that have limited impacts from
hydroelectric turbines, including the Mississippi watershed (which has
few hydroelectric facilities) (Wege 2006, pp. 5-6).
The impacts from turbines to the American eel, experts have
suggested, could result in a decrease in local or regional abundance,
as well as a population skewed toward smaller and younger females and
more males, and together these changes in the population could
ultimately result in a decline in recruitment (USFWS 2005b, p. 34). In
analyzing the effects of turbines on the American eel, however, we also
took into account that turbines principally affect freshwater
inhabitants, leaving the portion of the population that inhabits
estuarine and marine waters largely unaffected (USFWS 2005b, p. 3). As
a consequence, a decline resulting specifically from turbine mortality
may be buffered by the spawning input from eels residing in unaffected
freshwater habitats, or the estuarine or marine habitats throughout its
wide range.
It was also suggested by experts that the importance of turbines as
a population threat can be assessed only in the context of a general
understanding of distribution and dispersal patterns of the eel.
Specifically, a watershed's specific reproductive contribution rates
and size distribution of females needs to be accounted for in
determining the impact of turbines on anything larger than a watershed
level basis (USFWS 2005b, p. 31). Currently there is no such rangewide
estimate.
In lieu of this rangewide estimate, we can look at whether there
has been an impact to the American eel population, and if so, if it
relates to the construction of hydropower facilities. As is discussed
under Population Status, there does not appear to be a rangewide
decline in recruitment of juvenile eels; therefore, we can draw no
connection between turbine mortality and population level impacts.
Additionally, according to Castonguay et al. (1994a, p. 486), the
timing of the 1980s decline of the American eel in the upper SLR/LO
does not correlate with the human-caused changes that occurred on the
St. Lawrence River prior to 1965.
In summary, turbines, particularly multiple turbines within a
watershed or turbines on terminal dams, can cause substantial mortality
within those watersheds. However, turbines are present on a small
portion of the dams within the Atlantic coast and are absent from most
of the barriers encountered in the Mississippi Watershed, and there
remains a percentage of successful eel passage through turbines or with
spill over the top of dams. Additionally, there is no evidence of a
population level effect from turbine mortality. We conclude that
turbines are responsible for decreases in abundance on a local or
regional scale, but turbine mortality is not a significant threat to
the American eel at a population level.
Contaminants
During the status review, we developed a summary of the current
American eel contaminant literature (Roe 2006, pp. 1-26), and analyzed
the impacts of: (1) Existing contaminants on the American eel life
cycle, including levels of uncertainty, and particularly the inability
to successfully raise eels and consequently study the impacts of
contaminants on any of the eel life stages; (2) new and emergent
contaminants; (3) other persistent contaminants, such as genotoxic
polycyclic aromatic hydrocarbons (PAHs); (4) non-persistent
contaminants, such as pharmaceutical chemicals and pesticides; (5)
complex mixtures of contaminants; (6) vitamin deficiency related to
diet; and (7) combined threats, such as disease,
[[Page 4993]]
parasites, and contaminants, on eel health.
(1) Existing Contaminants
Concentrations of polychlorinated biphenyls (PCBs), PAHs,
polychlorinated diphenyldioxins/polychlorinated diphenyl furans (PCDDs/
PCDFs), pesticides such as mirex and di chloro di phenyl tri chloro eth
ane (DDT), and metals such as mercury were reported in yellow and
silver American eel tissues from eastern U.S. and Canadian waters.
However, much uncertainty exists with regard to the population's
rangewide contaminant load since environmental contaminant data were
only available from a small portion of the species' range; therefore,
the contaminant loads within American eel throughout its entire
population range are unknown.
The contaminant concentrations reported in American eel tissues are
within the range of concentrations associated with impacts that have
been documented in other fish species. These environmental contaminants
have been shown to have biochemical, immunological, genotoxic
(chemicals toxic to DNA), growth, survival, and reproductive impacts on
various fish species. We believe that contaminants therefore have the
potential to also impact the American eel (Roe 2006, pp. 5-8).
Interestingly, American eels survive with these contaminant loads at
concentrations that would be toxic to other fish species. There is,
however, a potential for the impacts to be fully expressed during
critical periods of their life cycle such as metamorphosis, hatching,
and larval development (Robinet and Feunteun 2002, pp. 267, 270-272),
all of which occur at sea and therefore are currently impossible to
research under natural conditions (USFWS 2006, p. 24-27). Because of
this species' unique life history, caution was suggested in utilizing
surrogate species data in determining impacts of contaminants on eels
(USFWS 2006, p. 24).
Inability to successfully study contaminants on all American eel
life stages. To date, researchers have not been able to successfully
complete the eel life cycle in the laboratory (Penderson 2003 pp. 324,
336-337; Palstra et al. 2005, pp. 533-534). Research has also not been
conducted on the impacts of contaminants on eel embryos and
leptocephali, or during metamorphosis from the yellow to silver eel
stage, or during outmigration and reproduction. Two recent laboratory
studies on the reproductive capacity of European eels by van den
Thillart et al. (2005, pp. 110, 169) and Palstra et al. (2006, pp. 147-
148) indicated that preliminary studies of PCB and dioxin-like
contaminant impacts to maturation and fertilization showed negative
impacts on egg quality and embryonic development. However, artificial
hormone inducement of maturation in European eels is complicated by
high female adult mortality rates and high rates of embryo death after
fertilization (Pedersen 2003, pp. 336-337; Knights submitted, pp. 1-2).
Therefore, it is difficult to be certain whether the mortality rates
are associated with artificial maturation or fertilization techniques
or with exposure to contaminants (Knights submitted, p. 2). Unless or
until the issue of embryo death can be attributed exclusively to the
presence of contaminants, the data is still inconclusive with regard to
the determination of the impacts of PCB and dioxin-like contaminants at
a population level in the American eel.
(2) New and Emergent Contaminants
The impacts of new and emergent chemical contaminants in fish are
unclear and not available for the American eel. An example of new and
emergent contaminants presented during the workshop (USFWS 2006) was
polybrominated diphenyl ethers (PBDEs), a group of chemicals used as
flame retardants in a multitude of consumer products (Agency for Toxic
Substances and Disease Registry or ATSDR 2004, pp. 11-12). PBDEs are
similar to PCBs in that they are lipophilic, persistent in the
environment, and bioaccumulate in organisms. However, the impacts to
fish and other aquatic organisms have not been completely defined in
the scientific literature. There is evidence that PBDEs cause enzyme
activity alterations and delayed embryonic hatching in fish, and they
result in behavioral alterations (Timme-Laragy et al. 2006, pp. 1098-
1103). Concentrations of PBDEs have been measured in European eels (de
Boer 1990, pp. 315-318; Covaci et al. 2004, pp. 3851-3855) and in other
species (Lebeuf et al. 2004, pp. 2973-2976); however, the impacts of
PBDEs to eels were not discussed. Therefore any impacts to the American
eel at a population level would be purely speculative.
(3) Impacts of Genotoxic Contaminants
The impacts of genotoxic PAHs on the eel remain uncertain. There is
considerable evidence that indicates a causal relationship between
exposure to PAHs and genotoxic impacts such as tumor frequency,
deformities, and other lesions in fish, particularly bottom feeding
fish (Black 1983, pp. 328-333; Metcalfe et al. 1990, pp. 133-139;
Baumann and Harshbarger 1995, pp. 168-170; Baumann et al. 1996, pp.
131-149; Johnson et al. 1998, pp. 125-134). Couillard et al. (1997, pp.
1918-1926) documented the occurrence of precancerous lesions in liver
tissues from migrating American eels from the St. Lawrence River. The
prevalence of the lesions in the eel liver tissue was reported to be
correlated with increasing contamination in eels, and the authors
concluded that PAHs may have been the cause (Couillard et al. 1997, p.
1924). Recent research in American eels (Schlezinger and Stegeman 2000,
pp. 378-384) and European eels (Doyotte et al. 2001, pp 1317-1320;
Bonacci et al. 2003, pp. 470-472; Mariottini et al. 2003, pp. 94-97)
has shown that induction of enzyme activity has also been used as a
biomarker for exposure to PAHs and similar contaminants. Genotoxic PAHs
may be impacting successful outmigration, but impacts of lesions and
tumors have not been researched under natural conditions or within the
laboratory.
(4) Non-Persistent Contaminants
Short-term exposure to non-persistent contaminants during critical
American eel life stages may be of concern (USFWS 2006, p. 25), but
uncertainty remains. The literature has shown that endocrine disrupting
environmental contaminants such as 4-nonylphenol (which is formed
during the industrial synthesis of detergents), and pesticides such as
atrazine and diazinon, cause physiological changes, inhibit growth, and
therefore inhibit the survival of wild Atlantic salmon (Salmo salar)
along the Canadian Atlantic coast (Moore and Waring 1996, p. 758;
Fairchild et al. 1999, p. 349; Brown and Fairchild 2003, p. 146;
Arsenault et al. 2004, p. 255; Waring and Moore 2004, p. 93). American
eels are sporadically exposed to relatively high concentrations of non-
persistent contaminants during their migration through the St. Lawrence
River to the Sargasso Sea (Pham et al. 2000, p. 78). For example, the
largest primary physio-chemical municipal sewage treatment plant in
North America is located in Montreal, and treated effluent is
discharged to the St. Lawrence River (Environment Canada 2006, pp. 1-3;
USFWS 2006, p. 25). At this location, there is evidence of endocrine
disruption in other aquatic organisms exposed to the effluent from 50
km upstream to 50 km downstream of the plant (Aravindakshan et al.
2004, pp. 156-164; Gagn[eacute] et al. 2004, pp. 33-43).
[[Page 4994]]
However, currently there is no information within the literature on the
sensitivity of eels to short-term exposure to these potentially
endocrine disrupting non-persistent contaminants.
(5) Exposure to Complex Mixtures of Contaminants
The cumulative impacts of complex mixtures of contaminants on eel
species are unknown. Fish and other wildlife are not exposed to just
one single contaminant in the aquatic environment. Contaminants mixed
together may interact and have additive (Dioxin-like contaminants: Safe
1990, pp. 71-73; Van den Berg et al. 1998, pp. 775-776) or synergistic
(PAHs: Wassenberg and Di Giulio 2004, p. 1662) effects.
(6) Vitamin Deficiency Related To Diet
In addition to contaminant-induced impacts discussed above,
decreased concentrations of antioxidant vitamins may also be impacting
American eel survival, but this remains uncertain. Deficiences of
antioxidant vitamins, such as thiamine, vitamin B1, and astaxanthin (a
precursor to vitamin A), have been associated with increased early
mortality in salmon and trout species (Fitzsimons 1995a, p. 267;
Fitzsimons 1995b, pp. 286-288; Vuorinen et al. 1997, pp. 1151-1163;
Fitzsimons et al. 2001, p. 229). It has been suggested that the
occurrence of the early mortality syndrome in Lake Ontario lake trout
is related to alewife (Alosa pseudoharengus) and their high thiaminase
content (Fitzsimons 1995b, p. 288). Thiaminase are a group of enzymes
that break down thiamine in the body and Alewife is a common food item
for young trout. Because alewife are also consumed by American eels it
has been hypothesized that American eels in Lake Ontario may be
experiencing effects from reduced levels of thiamine. However, because
this hypothesis has yet to be tested this theory remains speculative.
(7) Impacts of Combined Threats
Finally, contaminants can impact the immune system and therefore
increase the organism's susceptibility to other threats such as
diseases, parasites, and bacterial and viral infections (Arkoosh et al.
1996, pp. 1154-1161, Arkoosh et al. 1998, p. 182; Grassman et al. 1996,
p. 829; Couillard et al. 1997, p. 1916; Johnson et al. 1998, p. 125;
Van Loveren et al. 2000, p. 319; Zelikoff et al. 2000, p. 325), but the
effect on the American eel remains uncertain. The cumulative stress of
the complex mixtures of environmental contaminants and other threats
may potentially lead to increased mortality. Field studies have
documented susceptibility to infections in European and North American
fish species (Arkoosh et al. 1998, pp. 188-189; Van Loveren et al.
2000, pp. 322-323; Zelikoff et al. 2000, pp. 325-330), which would make
these fish more susceptible to disease. Bacterial pathogens have been
isolated in American eels, and the authors suggested that increased
prevalence of these pathogens may potentially be related to stress and
subsequent decreased immune resistance (Hayasaka and Sullivan 1981, p.
658; Davis and Hayasaka 1983, pp. 559, 561; see Factor C).
In summary, contaminants may impact early life stages of the
American eel, but we remain cautious in extrapolation of these
preliminary laboratory studies with regard to rangewide implications
without specific information. A correlation between the contamination
of the upper SLR/LO and the timing of the 1980s decline of American eel
in the upper SLR/LO is not evident (Castonguay et al. 1994a, pp. 482-
483), and current environmental laws and regulations have significantly
decreased the discharge of many persistent environmental contaminants.
Given the absence of evidence for population-level effects, such as
reduced recruitment of glass eels (which would be an indicator of
decreased outmigration survival, or egg or leptochephali survival as a
result of the impacts of contamination), we believe that the available
information on contaminants does not indicate a significant threat to
the American eel at a population level.
Because spawning and egg and leptochephali maturation occurs in the
open ocean, directly study of the effects of contaminants under natural
conditions will continue to be difficult. This emphasizes the need for
data collection and analysis designed to differentiate between
population fluctuations responding to natural phenomena such as oceanic
conditions and those that are human-caused. We support the continuation
and expansion of the coastwide monitoring program started several years
ago, and the ongoing research being conducted by the scientific
community.
Oceanic Conditions
During the status review, we explored the relationship between
oceanic conditions and the recruitment of leptocephali to coastal and
riverine habitats both hypothetically and through correlative data.
Additionally, we investigated and describe briefly here the types of
oceanic conditions that have the potential to impact American eels.
Finally, we analyzed the potential for oceanic conditions to impact the
American eel at a population level.
Variations in oceanic conditions have been linked to wide-ranging
and long-term changes in many fish, invertebrate, and zooplankton
species. General ecological responses to oceanic variations encompass
changes in timing of reproduction, egg viability, timing of food
availability, larval growth and mortality, population sizes, spatial
distribution, and inter-specific relationships (such as competition and
predator-prey relationships), by affecting temperature, salinity,
vertical mixing, circulation patterns, and ice formation. However, the
relationships are complex, usually non-linear, and operate through
complex mechanisms through several trophic levels over the ecosystem,
and over a broad range of time and spatial scales (Colbourne 2004, p.
16). Further, a population's response is likely to vary in different
regions (Ottersen et al. 2001, pp. 1-14; Attrill and Power 2002, pp.
275-278; Hurrell et al. preprint, p. 10, 22-25, 38; Perry et al. 2005,
p. 1-4; Weijerman et al. 2005 abstract and appendix 2, p. 3).
Oceanic conditions likely play a significant role in the population
dynamics of American eel (Knights et al. 2006, p. 2), but the
relationships between specific oceanic conditions and eel recruitment
remain almost entirely hypothetical. Changes in oceanic conditions have
previously been thought not to be correlated with the decline in the
upper SLR/LO (Castonguay et al. 1994b, p. 6; ICES 2001, p. 5). To
better understand this complex relationship given the scant available
literature, we requested assistance from oceanic and eel experts. Part
of the assistance was a summary of all available literature, entitled
American Eel Leptocephali-Larval Ecology and Possible Vulnerability to
Changes in Oceanographic Conditions, by M. Miller of the Ocean Research
Institute at the University of Tokyo (cited as Miller 2005).
Additionally, we examined published and unpublished data on the topic
(Knights, Friedland, Casselman, Miller, Kritzer, and Govoni in USFWS
2005b, pp. 50-65).
The types of oceanic conditions that have the potential to affect
eels in the North Atlantic include: (1) Changes to sea surface
temperatures (SSTs); (2) changes to mixed layer depth (MLD); (3)
deflections of the Gulf Stream at the Charleston Bump and Cape
Hatteras; and (4) other changes. Changes of SSTs include inhibition of
spring mixing, and nutrient recirculation and productivity, which may
influence leptocephali food
[[Page 4995]]
abundance. MLD (the depth to which mixing is complete, relative to the
layer of ocean water beneath it) changes include changes in size and
depth of leptocephali habitat, which would affect leptocephali
abundance, survival, or transport. Changes in the Gulf Stream could
interrupt migration by slowing or removing leptocephali from the Gulf
Stream, and any transport and subsequent recruitment problems might be
accentuated at the extremes of the species' range. The ``other''
category included changes to other aspects of the Gulf Stream, such as
the formation of eddies, which may spin leptocephali off of the main
current (USFWS 2005b, p. 53).
Variation in oceanic conditions is often depicted by the North
Atlantic Oscillation Index (NAOI). The NAOI is a measure of oceanic-
climate changes, expressed as the difference in atmospheric pressure
measured between Greenland and the Azores. The NAOI has phases
(positive and negative) that have important oceanographic effects. For
example, a positive (high) NAOI is indicated by periods of stronger
winds, greater surface-water mixing, reduction of the Gulf Stream,
shift of the Gulf Stream in a northeast direction, and increases in
deep water formation and water mass formation in the Labrador Sea (and,
it is hypothesized, weak eel recruitment); a negative NAOI shifts the
Gulf Stream south and increases the transport in the Labrador Current
(the western boundary current of the North Atlantic subpolar gyre) (and
it is hypothesized, a strong eel recruitment). These oscillations
correlate with other oceanic factors such as MLD, SST anomalies, and
position of the North Wall (a steep water temperature gradient) of the
Gulf Stream (for further discussion of NAOI see Weijerman et al.
Appendix 2, pp. 3, 9).
The NAOI has received considerable attention because of its strong
negative correlation with recruitment of European eels (glass eels
recruited to den Oever, Netherlands) (ICES 2001, p. 5) and a similar,
but weaker, negative correlation with recruitment of American eels
(juvenile eels recruited to the St. Lawrence River) (ICES 2001, p. 5;
Cairns et al. 2005, Table 9.2, p. 66). From the mid 1950s to 1978/1979
winter the NAOI was in a 24 year negative phase. From 1979/1980 winter
to 1994/1995 winter the NAOI was in a positive phase (Weijerman et al.
Appendix 2, pp. 3, 9) and this positive phase may have continued until
recently. During this prolonged positive (high) phase European eel
recruitment had been correspondingly low (ICES 2002, p. 2). The last
few winters, however, have not been strongly positive (Hurrell et al.
preprint, p. 4), which may indicate that the NAOI is beginning to shift
to a negative phase, which would benefit eels (USFWS 2005b, p. 66). A
shift to a negative phase would be consistent with the observation that
the NAOI seems to follow 7- to 8-year cycles, superimposed on 20- to
30-year cycles (Knights 2003, p. 238).
The correlation between NAOI and recruitment suggests that oceanic
conditions are currently the most influential variable affecting
recruitment. As noted earlier, efforts to model the population dynamics
of American eel are inherently limited by sparse or nonexistent data.
Nonetheless, sensitivity analysis of one modeling effort indicated that
oceanic conditions had greater eel population effects than fishing,
dams, or other habitat impacts (BEAK 2001, pp. 5.10-5.11).
In summary, oceanic conditions influence growth, recruitment, and
distribution of many marine species. The interactions between the
marine environment and production of marine species, however, are
exceedingly complex. Although the interactions are not completely
understood, the success of early eel life stages and subsequent
recruitment to fresh water is dependant on oceanic conditions, which
are subject to natural variation. Natural conditions can, when a
species is significantly reduced in range or abundance, be considered a
threat. However, there is no indication that the American eel is
suffering this level of reduction in either abundance or range.
Therefore, because oceanic conditions are within normal variations, the
American eel is evolutionarily adapted to oceanic variations, and there
is no indication that the American eel is at a reduced level where this
natural oceanic variation would significantly affect the species, we
have concluded that oceanic conditions are not now, and there is no
information indicating oceanic conditions should be in the future, a
significant threat to the American eel at a population level.
Summary of Factor E
In conclusion, hydropower turbines are a source of ongoing
mortality. This mortality has affected, and will continue to affect,
regional presence and abundance of eels. However, the current
information does not provide evidence to support turbines as a
significant threat to the American eel at a population level. There is
substantial uncertainty on the effects of contaminants on the American
eel and more research is needed. However, after examination, the
literature does not support a population level impact from
contaminants. Oceanic conditions are highly variable and cyclical. They
determine recruitment to the continent, and therefore they have a
substantial influence on the presence and abundance of eels on the
continent, particularly in freshwater habitats. Oceanic conditions are
a naturally occurring influence on the American eel during its early
life history, and are not a significant threat to the American eel. In
sum, given the absence of evidence for population-level effects, such
as reduced recruitment of glass eels, we have concluded that there is
not supporting data to indicate other natural or manmade factors as a
significant threat to the American eel.
Finding
The Act defines the term ``threatened species'' as any species (or
subspecies or, for vertebrates, distinct population segment) that is
likely to become an endangered species within the foreseeable future
throughout all or a significant portion of its range. The term
``endangered species'' is defined as any species that is in danger of
extinction throughout all or a significant portion of its range. The
principal considerations in the determination of whether a species does
or does not warrant listing as a threatened or endangered species under
the Act are the threats that confront the species, as discussed in the
five factor analysis above.
In reviewing the status of the American eel, we make the following
findings. The species has been extirpated from some portions of its
historical freshwater habitat over the last 100 years or so, mostly as
a result of dams built by the late 1960s. There is also evidence that
the species' abundance within freshwater habitats, and to some degree
estuarine habitats, has declined in some areas (e.g., upper SLR/LO and
the Chesapeake Bay) likely as a result of harvest or turbine mortality,
or a combination of factors. However, the species remains widely
distributed over the majority of its historical range. Based on
information from the ASMFC stock assessment and peer review and the
COSEWIC Assessment and Status Report, an indication of decline exists
in yellow eel abundance, but recent glass eel recruitment trends,
although variable from year to year, appear stable over the past 15
years. The American eel is a highly resilient species, with the ability
to occupy the broadest range of habitats within freshwater, as well as
estuarine and marine waters, and it remains a widely distributed fish
species. The lack
[[Page 4996]]
of population subdivision (i.e., panmixia) in the American eel provides
resilience to genetic problems that can result from decline and
isolation of subpopulations.
Although roughly 25 percent of the American eel's historical
freshwater habitat is now inaccessible due to dams, the loss of this
habitat does not threaten the species' long-term persistence. This is
because a large amount of freshwater habitat still remains (roughly 75
percent of historic freshwater habitat in the United States remains
available and occupied by the American eel), from which both males and
females outmigrate, and because a portion of American eels complete
their life cycle in estuarine and marine waters without entry into
freshwater. Although the significance of the estuarine and marine eel
contribution to reproduction is considered speculative by some, a
growing number of researchers think the contribution could be
substantial (Tsukamoto and Arai 2001, p. 275; Jessop 2002, p. 228;
Kotake et al. 2005, p. 220; Cairns 2006a, p. 1; Knights et al. 2006,
pp. 12-13), and there is no doubt that substantial amounts of estuarine
and marine waters remain available to and are occupied by the American
eel throughout its range.
The threat of Sargassum harvest is no longer considered a threat
due to new information indicating that the American eel larvae do not
utilize Sargassum, and due to regulations restricting its harvest.
Recreational and commercial eel harvests are no longer factors of
concern at a population level due to economics, the species'
resilience, and existing regulatory mechanisms. Although mortality
during outmigration due to parasites and contaminants, and the
potential effects of contaminants on early life stages, remain a
concern, we have no information indicating that these threats are
currently causing or are likely to cause population level effects to
the American eel. We have no information indicating that predation or
competition with nonnatives or mortality from turbines are causing
population-level effects. Recruitment success of the American eel is
dependent on ocean conditions, and variation in ocean conditions causes
fluctuation in recruitment. However, because the available information
indicates that the species remains widely distributed and glass eel
recruitment trends appear stable over the past 15 years, observed ocean
conditions do not threaten the current population status of the
American eel. Also, we have no information to indicate that ocean
conditions are likely to threaten the American eel at a population
level in the future.
In reviewing the status of the American eel, we also considered
whether there was any area where the species is threatened or
endangered throughout a significant portion of its range. We considered
threats to its spawning, migratory, and growth habitats (see discussion
under Factor A and Ocean Conditions in Factor E) and found no area
where the species is threatened or endangered throughout a significant
portion of its range. The Sargasso Sea, where the American eel spawns,
is for that reason a significant portion of the range, but we
identified no threats to this habitat. Similarly, the open ocean
migratory habitat of the American eel is also a significant portion of
the range, but we identified no threats to this habitat either.
The American eel's growth habitat consists of those areas, apart
from its spawning and migratory habitats, where the species' growth
primarily takes place. We evaluated whether the upper SLR/LO, an area
of the American eel's growth habitat that has experienced an extreme
decline in American eel abundance, is a significant portion of the
range. The American eel is panmictic, genetically homogeneous, and
capable of occupying a diversity of growth habitats. It currently
occupies a number of growth habitats, each of which is similar in
habitat characteristics. Therefore no one growth habitat would be a
significant portion of the range unless it was significant in terms of
eel reproductive contribution. Although it has been suggested that the
upper SLR/LO historically contributed a disproportionately larger
amount of reproduction than other freshwater areas of similar size,
significant uncertainties have been identified regarding this analysis
(COSEWIC 2006, pp. 35-41). Even if the upper SLR/LO had historically
contributed a disproportionately larger amount of reproduction than
other freshwater areas of similar size (see Population Status in
Background section), our consideration of the data on facultative
catadromy (the ability to grow and become sexually mature in estuarine
and marine waters in addition to freshwater) suggests that the total
reproductive contribution from the rest of the range (including other
freshwater and all estuarine and marine waters) outside the upper SLR/
LO is substantially greater than the historical reproductive
contribution from the upper SLR/LO (see Population Status in Background
section). Consequently, any historical additional reproductive
contribution from the upper SLR/LO does not make this area
significantly more important than if its historical reproductive
contribution was similar to that of other similarly sized areas within
the range of the species. Because the upper SLR/LO area does not
contain any unique or particularly high-quality habitat, does not
contribute to any genetic differences, contains substantially less than
50 percent of the growth habitat for the eel, and does not appear to
contribute greatly to the long-term persistence of the species, we have
determined that it is not a significant portion of the range. In
addition, even if the SLR/LO were to be considered a significant
portion of the range we find from the record before us that the eel is
not threatened or endangered in the SLR/LO because eels will likely
persist there into the foreseeable future (for discussion of this
``rescue effect'' see Background, Population Status). The American eel
is panmictic and substantial reproductive contribution comes from
outside the upper SLR/LO. We believe that the upper SLR/LO will likely
continue to receive eels and, therefore, extirpation of eels from the
upper SLR/LO is unlikely.
In addition, we considered whether there are any segments of the
population of American eel that would qualify as distinct population
segments (DPSs) under the USFWS's Policy Regarding the Recognition of
Distinct Vertebrate Population Segments Under the Endangered Species
Act (DPS Policy) (USFWS 1996). To be identified as a DPS, a population
must satisfy both the discreteness and significance tests of the DPS
Policy. Because the species is panmictic (a single inter-breeding
population), no part of the species' population meets the discreteness
test of the DPS policy. Because no discrete populations can be
identified, there are no populations for which we could evaluate
significance. Therefore, no American eel DPSs can be recognized.
Due to the concerns about the status of the American eel in Canada,
we considered delineation of a Canadian DPS using the international
border. However, we determined that the Canadian population of American
eels would not satisfy the significance test. There is no evidence to
suggest that eels in Canada are genetically different from eels in
other parts of the species' range, that eels in Canada inhabit a unique
ecological setting, that loss of eels in Canada would result in a
significant gap in the range of the species, or that the Canada
population of eels otherwise could be considered significant under the
DPS policy. Also, because the species is panmictic and juveniles are
distributed randomly over a wide range,
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and because substantial reproductive contribution occurs over most of
the range, Canada will likely continue to receive eels despite any
reduction in yellow eel abundance in Canada. Therefore, the Canadian
population would not be considered endangered or threatened and as a
result would not qualify as a DPS under the DPS policy.
In summary, we find that the American eel remains widely
distributed over their vast range including most of their historic
freshwater habitat, eels are not solely dependent on freshwater habitat
to complete their lifecycle utilizing marine and estuarine habitats as
well, they remain in the millions, that recruitment trends appear
variable but stable, and that threats acting individually or in
combination do not threaten the species at a population level. On the
basis of the best available scientific and commercial information, we
conclude that the American eel is not likely to become an endangered
species within the foreseeable future throughout all or a significant
portion of its range and is not in danger of extinction throughout all
or a significant portion of its range. Therefore, listing of the
American eel as threatened or endangered under the Act is not
warranted.
Author
The primary author of this finding is Heather Bell, Fisheries
Biologist, Region 5, USFWS, 300 Westgate Center Drive, Hadley,
Massachusetts, 01035.
References Cited
A complete list of all references cited is available on request
from the U.S. Fish and Wildlife Service's Region 5 Regional Office (see
ADDRESSES section above).
Authority: The authority for this action is the Endangered
Species Act of 1973, as amended (16 U.S.C. 1531 et seq.).
Dated: January 23, 2007.
Kevin Adams,
Acting Director, U.S. Fish and Wildlife Service.
[FR Doc. 07-429 Filed 2-1-07; 8:45 am]
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