Endangered and Threatened Wildlife and Plants; 12-Month Finding on a Petition To List the American Eel as Threatened or Endangered, 4967-4997 [07-429]

Agencies

• Fish and Wildlife Service
• DEPARTMENT OF THE INTERIOR

[Federal Register Volume 72, Number 22 (Friday, February 2, 2007)]
[Proposed Rules]
[Pages 4967-4997]
From the Federal Register Online via the Government Printing 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 AmericanEel@fws.gov.

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 
https://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 https://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 var