Federal Register / Vol. 72, No. 22 / Friday, February 2, 2007 / Proposed Rules 4967 

hearing for scheduling those who have 

not notified the EPA contact earlier. 

This testimony will be scheduled on a 

first-come, first-served basis to follow 

the previously scheduled testimony. 

EPA requests that approximately 50 

copies of the statement or material to be 

presented be brought to the hearing for 

distribution to the audience. In 

addition, EPA would find it helpful to 

receive an advance copy of any 

statement or material to be presented at 

the hearing at least one week before the 

scheduled hearing date. Such advance 

copies would give EPA staff adequate 

time to review the materials before the 

hearing. Advance copies should be 

submitted to the EPA contact person 

listed in this proposal. The official 

records of the hearing will be kept open 

until the close of the comment period to 

allow submission of rebuttal and 

supplementary testimony. 

Materials relevant to this notice, 

including the regulatory language, are 

contained in the Public Docket ID No 

EPA–HQ–OAR–2006–0841. Publicly 

available docket materials are available 

either electronically in http:// 

www.regulations.gov or in hard copy at 

the Air Docket, EPA/DC, EPA West, 

Room B102, 1301 Constitution Ave., 

NW., Washington, DC. The Public 

Reading Room is open from 8:30 a.m. to 

4:30 p.m., Monday through Friday, 

excluding legal holidays. The telephone 

number for the Public Reading Room is 

(202) 566–1744, and the telephone 

number for the Air Docket is (202) 566–

1742. 

The hearing will be conducted 

informally, and technical rules of 

evidence will not apply. A written 

transcript of the hearing will be placed 

in the docket for review. Anyone who 

desires to purchase a copy of the 

transcript should make individual 

arrangements with the court reporter 

recording the proceeding. 

Dated: January 26, 2007. 

Margo Tsirigotis Oge, 

Director, Office of Transportation and Air 

Quality. 

[FR Doc. E7–1726 Filed 2–1–07; 8:45 am] 

BILLING CODE 6560–50–P 

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. 

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 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 


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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, 


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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 recolonize 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 °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/100m3 and as low as 1.5 eels/100m3

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 markVerDate Aug<31>2005 14:13 Feb 01, 2007 Jkt 211001 PO 00000 Frm 00006 Fmt 4702 Sfmt 4702 E:\FR\FM\02FEP1.SGM 02FEP1

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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 

rivie`re del la Trinite ́ 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 markrecapture 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/m2) (which may lead to 

predation, including cannibalism, 

starvation, and competition for space), 

and predation by resident, presumably 

older, eels. V<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, densitydependent 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 


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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<llestad and Jonsson1988 in Jessop 

2000, p. 522; V<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 (outmigration), 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 


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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 

Boe ̈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° to 63°) 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 recolonize areas once the threat has 

abated. 

BILLING CODE 4310–55–P 


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It has been reported in other 

documents that Boe ̈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 humanmade barriers, eels occupy all 

freshwater systems, including large 

rivers and their tributaries, lakes, 

reservoirs, canals, farm ponds, and even 

subterranean springs. The anquillid (eelshaped) 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 100m2. 

In Lake Champlain, Vermont, densities 

ranged from 2.32–6.36 eel/100m2 (LeBar 

and Facey 1983 in Machut 2006, p. 50). 

In a tidal creek, Georgia, densities 

ranged from 1.82–2.32 eel/100m2

(Bozeman et al. 1985 in Machut 2006, p. 

50). A Massachusetts salt marsh yielded 

densities of 8.46–9.28/100m2 (Ford and 

Mercer 1986 in Machut 2006, p. 50). In 

Machut’s own study in the Hudson 

River freshwater tributaries densities 

ranged from 0.28–155.06/100m2

(Machut 2006, p. 50), while in brackish 

waters Morrison and Secor (2003 in 

Machut 2006, p. 50) reported densities 

of 0.03–0.24/100m2 . In four Maine 

freshwater rivers, densities ranged from 

1.80–35.40/100m2 (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/100m2. On 

the North Anna River, where the eels 

were smaller, the population estimate 

was greater at 4.48/100m2 (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 intraor 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, 


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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), E ́deline and E ́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 freshseekers 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 km2) exceed that of freshwater 

(1,035 km2). 

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 


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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 postfishery 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; 


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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 


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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 swimbladder 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 semienclosed 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 


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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 AlbemarlePamlico Sound. The Chesapeake Bay 

and its tidal tributaries have over 11,000 

miles of shoreline; this is more than the 

entire West coast. The AlbemarlePamlico 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 wellknown 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 


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(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 MosesSaunders dam only through the WileyDondero 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 MosesSaunders 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 


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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 

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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 densitydependent 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, markrecapture 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 Stateregulated 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 


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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<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 °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 nonadapted 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). Wu ̈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 fixedblade 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. Monteˆn (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, 


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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 

dichlorodiphenyltrichloroethane (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 dioxinlike 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 physiochemical 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; Gagne ́ et al. 2004, pp. 33–43). 


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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 longterm 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 


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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 


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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 longterm 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] 

BILLING CODE 4310–55–P 


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