REFF9.E?-F",OPY 

Do Not Remove from the Library 

U. S. Fish and Wildlife Service 

~esearch Center TR EL-82-4 ~iological Report 82 (11-74) 700 Cajun Dome Boulevard 

AU~US~ 1987 La fayette, Louisiana 70506 

Species Profiles: Life Histories and 

Environmental Requirements of Coastal Fishes 

and Invertebrates (North Atlantic) 

AMERICAN EEL 

Fish and Wildlife Service Waterways ~xperiment station 

U.S. Department of the Interior U.S. Army Corps of Engineers 
Biological Report 82(11.74) 

TR EL-82-4 

August 1987 

Species Profiles: Life Histories and Environmental Requirements 

of Coastal Fishes and Invertebrates (North Atlantic) 

AMERICAN EEL 

Douglas E. Facey 

Department of Zoology 

University of Georgia 

Athens, GA 30602 

and 

Michael J. Van Den Avyle 

Georgia Cooperative Fish and Wildlife Research Unit 

School of Forest Resources 

University of Georgia 

Athens, GA 30602 

Project Manager 

Carroll Cordes 

Project Officer 

David Moran 

U.S. Fish and Wildlife Service 

National Wet1 ands Research Center 

1010 Gause Boulevard 

Sl idel 1 , LA 70458 

Performed for 

Coastal Ecology Group 

Waterways Experiment Station 

U.S. Army Corps of Engineers 

Vicksburg, MS 39180 

and 

U.S. Department of the Interior 

Fish and Wildlife Service 

Pesearch and Development 

National Wetlands Research Center 

Washington, DC 20240 
This series should be referenced as follows: 

U.S. Fish and Wildlife Service. 1983-19 . Species profiles: life histories 

and environmental requirements of coast3 fishes and invertebrates. U .S. Fish 

Wildl . Serv. Biol . Rep. 82(11). U.S. Army Corps of Engineers, TR EL-82-4. 

This profile should be cited as follows: 

Facey, D.E., and M.J. Van Den Avyle. 1987. Species profiles: life histories 

and environmental requirements of coastal fishes and invertebrates (North 

Atlantic)--American eel. U.S. Fish Wildl . Serv. Biol . Rep. 82(11.74). U.S. 

Army Corps of Engineers, TR EL-82-4. 28 pp. 
PREFACE 

This species profile is one of a series on coastal aquatic organisms, 

principally fish, of sport, commercial, or ecological importance. The profiles 

are designed to provide coastal managers, engineers, and biologists with a brief 

comprehensive sketch of the biological characteristics and environmental 

requirements of the species and to describe how populations of the species may be 

expected to react to environmental changes caused by coastal development. Each 

profile has sections on taxonomy, 1 ife history, ecological role, environmental 

requirements, and economic importance, if appl icable. A three-ring binder is 

used for this series so that new profiles can be added as they are prepared. 

This project is jointly planned and financed by the U.S. Army Corps of Engineers 

and the U.S. Fish and Wildlife Service. 

Suggestions or questions regarding this report should be directed to one of 

the foll owing addresses. 

Information Transfer Specialist 

National Coastal Ecosystems Team 

U.S. Fish and Wildlife Service 

NASA-Sl idel 1 Computer Complex 

1010 Gause Boulevard 

Slidell, LA 70458 

U. S. Army Engineer Waterways Experiment Station 

Attention: WESER-C 

Post Office Box 631 

Vicksburg, MS 39180 
CONVERSION TABLE 

Metric to U.S. Customary 

Multiply 

millimeters (mm) 

centimeters (cm) 

meters (m) 

meters (m) 

kilometers (km) 

kilometers (km) 

square meters (m2) 10.76 

square ki 1 ometers (km2) 0.3861 

hectares (ha) 2.471 

liters (1) 

cubic meters (m3) 

cubic meters (m3) 

milligrams (mg) 

grams (g) 

ki 1 ograms (kg) 

metric tons (t) 

metric tons (t) 

kilocalories (kcal) 

Celsius degrees (OC) 

inches 

inches 

feet (ft) 

fathoms 

statute miles (mi) 

nautical miles (nmi) 

square feet (ft2) 

square mi 1 es (mi2) 

acres 

gallons (gal) 

cubic feet (ft3) 

acre-feet 

ounces (02) 

ounces (02) 

pounds (lb) 

pounds (lb) 

short tons (ton) 

British thermal units (Btu) 

Fahrenheit degrees (OF) 

U.S. Customary to Metric 

25.40 

2.54 

0.3048 

1.829 

1.609 

1.852 

To Obtain 

inches 

inches 

feet 

fathoms 

statute mi 1 es 

nautical miles 

square feet 

square miles 

acres 

gal 1 ons 

cubic feet 

acre-feet 

ounces 

ounces 

pounds 

pounds 

short tons 

British thermal units 

Fahrenheit degrees 

millimeters 

centimeters 

meters 

meters 

kilometers 

kilometers 

square meters 

square kilometers 

hectares 

1 i ters 

cubic meters 

cubic meters 

milligrams 

grams 

ki 1 ograms 

metric tons 

metric tons 

ki localories 

Celsius degrees 
CONTENTS 

Page 

PREFACE .................................................................... iii 

CONVERSION TABLE ........................................................... i v 

ACKNOWLEDGMENTS ............................................................ v i 

NOMENCLATLIRE/TAXONOMY/RANGE ................................................ 1 

MORPHOLOGY/IDENTIFICATION AIDS ............................................. 3 

REASON FOR INCLUSION IN SERIES ............................................. 3 

LIFE HISTORY ............................................................... 4 

Spawning ................................................................. 4 

Larval (Leptocephal us) Stage ............................................. 5 

Glass Eel and Elver Stages ............................................... 6 

Yellow and Silver Eels ................................................... 8 

GROWTH CHARACTERISTICS ..................................................... 10 

COMMERCIAL AND SPORT FISHERIES ............................................. 11 

ECOLOGICAL ROLE .......... ................................................. 16 

ENVIRONMENTAL REQUIREMENTS ................................................. 17 

Temperature ............................................................. 17 

Salinity ................................................................ 17 

Dissolved Oxygen ......................................................... 18 

Habitat Structure ........................................................ 18 

River and Tidal Currents ................................................ 18 

Contaminants ............................................................. 18 

LITERATURE CITED ........................................................... 21 
ACKNOWLEDGMENTS 

We gratefully acknowledge the helpful comments and criticisms of Gene S. Helfman of the University of Georgia, Elizabeth D. Hubbard of the Massachusetts 

Division of Marine Fisheries, George W. LaBar of the University of Vermont, 

James D. McCleave of the University of Maine, and several anonymous reviewers 

at the National Wetlands Research Center. Janice M. Kerr prepared Figures 1 and 

3. We especially thank Sue J. Anthony for typing and formatting the manuscript. 
Figure 1. American eel. 

AMERICAN EEL 

Scientific name ...... Anguilla rostrata 

Preferred common name ......... American 

eel (Figure 1) 

Other common names ........... Anguille, 

ye1 1 ow eel, green eel , black eel , 1 ittle eel, bronze eel, glass eel, 

si 1 ver eel , river eel 

Class.. .................. .Osteichthyes 

Order ................... Auguilliformes 

Family ..................... Anguillidae 

Geographic range: Adults or various 

developmental stages commonly occur 

in freshwater, coastal waters, and 

the open ocean from the southern tip 

of Green1 and, Labrador, and 

Newfound1 and southward a1 ong the 

Atlantic coast of North America, 

into the Gulf of Mexico as far as 

Tampico, Mexico, and in Panama, the 

Greater and Lesser Antilles, and 

southward to the northern portion of 

the east coast of South America 

(Tesch 1977). The species is 

abundant in the North Atlantic 

states (Figure 2), the eastern 

Canadian provinces, and southward to 

Mexico; it is resident in the 

Mississippi Valley, and occurs in 

the West Indies and Bermuda. Bertin 

(1956) reported the latitudinal 

range for the American eel as 5" to 

62" N. It occurs in warm brackish 

and freshwater streams, estuaries, 

and coastal rivers, and sometimes in 

cold freshwater trout streams in 

mountainous regions. Its distribution has increased because of its 
Coastal distribution 

MILES 

A TL A N TIC OCEAN 

Figure 2. Major rivers that support the American eel in the North Atlantic 

United States. Eels also are common in other freshwater tributaries and in 

bays and estuaries. 
hardiness (as shown by the range of 

habitats it occupies, including polluted areas), the ease with which 

it can be transplanted, and its 

ability to travel across damp ground 

and wet vertical surfaces such as 

dams. Adult eels are occasionally 

found in landlocked lakes, primarily 

in the northeastern United States. 

MORPHOLOGY AND IDENTIFICATION AIDS 

The American eel undergoes a 

series of morphological changes in its 

life cycle, which are described in the 

later section on LIFE HISTORY. The 

fol 1 owing information was summarized 

primarily from Fahay (1978) and Tesch 

(1977). 

The body is elongate (Figure 1). 

The dorsal and anal fins are confluent 

with the rudimentary caudal fin. 

Pectoral fins are present, but ventral 

(pelvic) fins are absent. Scales form 

at about 3 to 5 years of age, but are 

minute and embedded, causing eels to 

appear scaleless. The lateral line is 

we1 1 developed. The mouth is 

terminal; the jaws have bands of 

small, pectinate, or setiform teeth, 

and the vomer has a long tooth patch. 

The number of vertebrae ranges from 

103 to 111 but usually is 106 to 108 

(Schmidt 1913). Ege ( 1939) presented 

comprehensive morphol ogical data for 

A. -rostrata. 

No other anguill id eels occur in 

North American coastal waters, but the 

American eel 's spawning area 

apparently overl aps with that of the 

European eel (An uilla anguilla) 

(McCleave et a1 . in myomere 

counts for American and European eel 

larvae are 106.84 + 0.032 S.E. and 

114.52 + 0.047 S.E. (Kleckner and 

McCl eave 1985). Externally visible 

traits of adults are similar, but the 

European eel has more vertebrae 

(111-119; mean,ll5). Some authors 

have argued that European and American 

eels should be regarded as geographical variants of the same species 

(Williams and Koehn 1984). Recent 

analysis of mitochrondrial DNA indicates that American and European eels 

belong to separate breeding populations (Avise et al. 1986). The lack 

of interbreeding even though the 

spawning areas overl ap supports the 

belief that American and European eels 

are different species. No available 

data conclusively point to geographic 

variations in morphology, and no 

subpopul ations have been distinguished. Koehn and Wil 1 iams (1978) 

noted protein differences among 

juvenile eels collected from different 

1 ocations a1 ong the At1 antic seaboard, 

but concluded that the differences 

were due to variation in selective 

pressures among the environments in 

which the eels grew. Avise et al. 

(1986) reported no significant 

geographic differentiation in the 

mitochondria1 DNA of 108 eels 

collected from Maine to Louisiana. 

This evidence strongly supports the 

conclusion that American eels are a 

single, panmictic breeding population. 

REASON FOR INCLUSION IN SERIES 

The American eel supports 

commercial and 1 imi ted recreational 

fisheries throughout most of its 

range. In the United States eels are 

marketed for human consumption and as 

bait for crabs and qame fishes, 

including striped bass (M - -. . , - 

orone 

saxatil is), cobia (Rachycentron 

canadur;lfr and largemouth bass 

(Microoterus . ~~ salmoides) . Adult eels 

often 'are shipped a1 i;e or frozen to . . Europe where they frequently are 

smoked before marketing. Elvers 

(immature eels typically < 60 mm 

long) have been harvested in Maine and 

shipped to Japan where they were 

cultured in ponds. Pond rearing of 

eels is being developed in the United 

States, and there is a potential for 

development and expansion of an eel 

culture industry. 

The American eel is an important 

food of larger marine and freshwater 
fishes. It preys on a variety of 

other animals includina commercially 

important crabs and clams. Eels 

ccntribute tc the loss cf nutrients 

from freshwater rivers avd lakes 

because of their high organic intake, 

large numbers, lengthy stay in freshwater, and subsequent migration to sea 

(Smith and Saunders 1955). 

LIFE HISTORY 

The life cycle of the Americav 

eel includes oceanic, estuarine, and 

riverine phases (Figure 3). Wany 

details of its life history are only 

generally understood or have been 

inferred from knowledge of the 

European eel. Much of what is kncwn 

has been derived from studies in the 

rnlgral~on rnlgratlon 

GLASS 

EEL 

&... 0 ' D ,OQ 

Figure 3. Diagrammatic representation 

of the life cycle of the American eel. 

4 

Middle and North Atlantic regions of 

the United States avd the eastern 

provinces of Canada. 

Different stages of the eel's 

life cycle are known by a variety of 

common names that are used throughout 

the scientific 1 i terature. The larva 

( l e p t o c e p h a l u s ) metamorphoses into an 

unpigmented glass eel which migrates 

into freshwater and gradually develops 

pigmentation. The young eel is now 

called an elver. Elvers may remain in 

coastal rivers or may continue to move 

upstream. The following growth phase, 

called the yellow eel, may last many 

:{ears. Ye1 low eels may be sexually 

undifferentiated (gonads contain no 

definable gametes), hermaphroditic 

(oogonia and spermatogonia present), 

or sexually differentiated (females 

with oogonia; males with spermatogonia). Because none of these stages 

are capable of reproduction, all 

ye1 low eels are immature. Maturation 

is accompanied by changes in body 

color and morphology; maturing eels 

that migrate downriver and through the 

ocean tc the spawning grounds are 

known as bronze eels or silver eels. 

Spawning 

The American eel is catadromous. 

It spends most of its l i f e i n rivers, 

freshwater 1 akes, and estuaries, but 

returns to the sea to spawn (Figure 

3). The age at maturity has not been 

we1 1 defined; Fahay (1978) reported 

that maturation occurred after age I11 

for males and at ages IV-VII for 

females from northerly populations, 

although females more than 15 years 

old have been reported in 1 arge inland 

lakes (Hurley 1972; Facey and LaBar 

1981). Eels mature at younger ages in 

the southeastern United States than in 

New England (Helfman et a1 . 19843; 

Hansen and Eversole 1984; Facey and 

He1 fman, in press). 

Before seaward migration in the 

fa1 1, maturing eels begin metamorphosis into the silver eel stage. 
(This metamorphosis and the timing of 

the reproductive migration are 

described 1 ater.) 

Spawning by American eel s has 

never been directly observed, and 

spawning areas have been inferred on 

the basis of collections of larvae. 

Spawning seemingly occurs in the 

Sargasso Sea as early as February and 

may continue until at least April 

(Kleckner et a1 . 1983; McCleave et al. 

1986). Tesch (1977), who summarized 

work by Schmidt (1923), Vladykov 

(1964), Smith (1968), and Vl adykov and 

March (1975), showed a spawning zone 

south of Bermuda and north of the 

Bahamas that is centered at about 25" 

N. and 69" W. McCleave et al. (1986) 

reported that American eels spawn in 

the area from 19.5" to 29.0" N. and 

52" to 79" W., and that European eels 

spawn from 23" to 30" N. and 48" to 

74" W. The youngest stages of 

American eel larvae may coexist with 

European eel larvae, but American eel 

larvae predominate west of 62" W. and 

south of 25" N. (Kleckner and McCleave 

1985). The large overlap of spawning 

areas between American and European 

eels is evidenced by the capture 

of leptocephali of both species in the 

same trawl (McCleave et a1 . 1986). 

Thermal fronts that separate the 

northern and southern water masses of 

the Sargasso Sea are believed to form 

the northern limit of American eel 

spawning (Kleckner et al. 1983). The 

smal lest American eel 1 eptocephal i 

that have been found (3.9-5.5 mm) were 

taken along the warm side of these 

fronts. 

The depth at which spawning 

occurs is not known, but morphological 

and physiological evidence suggests 

that eels may migrate and spawn in the 

upper few hundred meters of the water 

column (Kleckner et a1 . 1983; McCleave 

and Kleckner 1985). The smallest 

leptocephali yet reported were taken 

in trawls fished at a maximum depth of 

about 300 m (Kleckner et al. 1983). 

Egg diameter of A. rostrata is about 

1.1 mm (Tesch 1977). Incubation 

periods of American eel eggs are not 

known, but the eggs of artificially 

spawned Japanese eels (A. japonica) 

are known to hatch in 38x45 hours at 

23 "C (Yamamoto and Yamauchi 1974). 

Re1 ationships between eel size 

and fecundity for 21 eels (418-845 mm 

TL) were reported by Wenner and Musick 

(1974) as log F = -4.29514 + 3.74418 

log TL, log F = 3.2290 + 1.1157 log W, 

where F = number of eggs per female, 

TL = total length (mm), and W = total 

weight (g) . Therefore, fecundity for 

many American eels is between about 

0.5 and 4.0 million eggs, with very 

large individuals (1,000 mm) producing 

perhaps as many as 8.5 million eggs. 

The European eel has fecundity estimates of 0.7 to 2.6 million eggs for 

individuals 630-920 mm TL (Boetius and 

Boetius 1980). 

Adult eels presumably die after 

spawning. None have been observed 

to migrate up rivers, and spent eels 

have not been reported. 

Larval (Leptocephal us) Stage 

Hatching probably begins and 

peaks in February, but may continue 

through April (Kleckner et a1 . 1983; 

Kleckner and McCleave 1985; McCleave 

et al. 1986). The larval stage lasts 

up to about 1 year. The body is 

lanceolate, sharply pointed at both 

ends, and deepest at the middle; 

illustrations were published by Tesch 

(1977) and Fahay (1978). The length 

at hatching has not been described for 

the American eel ; however, the 

Japanese eel is about 2.7 mm long at 

hatching and about 6.2 mm long 5 days 

after hatching (Yamamoto and Yamauchi 

1974). Kl eckner et a1 . (1983) caught 

larval American eels less than 5.5 mm 

long (perhaps less than 1 week old) 

from mid-February to early March. 

Schmidt (1925) collected larvae 7 to 

8 mm long in February. The smallest 

larvae collected by Vladykov and March 

(1975) and Smith (1968) were 12 mm and 
17 mm, respectively, and were caught 

in the summer. 

American eel larvae grow as they 

are transported by ocean currents. 

Total lengths of larvae collected by 

Schmidt (1925) were 7 to 8 mm in 

February, 20 to 25 mm in April , 30 to 

35 mm in June, 40 mm in July, 50 to 55 

mm in September, and 60 to 65 mm by 

the end of the first year of life. 

The largest leptocephalus collected by 

Vladykov and March (1975) was 69 mm 

long. A thorough analysis of 

available data from 4473 larval and 

pos tmetamorphi c American eel s showed 

that the relationship between length 

(Y: mm TL) and collection date (X: 

Jul ian date) for 0-group leptocephal i 

collected between 13 February and 15 

October was Y=0.238 X - 6.569 (Kleckner and McCl eave 1985). 

Leptocephal i grow rapidly unti 1 

October when growth slows or stops, 

and many metamorphose into glass eels 

(Kleckner and McCleave 1985). Most 

leptocephal i undergo metamorphosis at 

55-65 mm TL and 8-12 months of age. 

Limited evidence suggests that some 

eels may remain in the leptocephalus 

stage for more than 1 year. Smith 

(1968) reported a leptocephalus 50 mm 

long near the spawning grounds during 

April ; it was thus too long to have 

been spawned in the immediate season 

(Fahay 1978). Vladykov and March 

(1975) also suggested that larval A. 

rostrata may spend more than 1 year in 

the sea. 

Larvae are transported from the 

spawning grounds to the eastern seaboard of North America by the Antilles 

Current, the Florida Current, and the 

Gulf Stream. Power and McCleave 

(1983) developed a model of surface 

current drift to simulate the dispersal of eel leptocephali from the 

Sargasso Sea. Sampling has shown that 

larvae are abundant in the Florida 

Straits and in the area between 

Bermuda and the Bahamas from April 

through August (Smith 1968). Most 

leptocephal i probably enter the Gul f 

Stream directly from the Sargasso Sea, 

rather than by a more southerly route 

through the Eahama Islands (Kleckner 

and McCleave 1982). Eldred (1971) 

found larval A. rostrata in the Gulf 

of Mexico an3 Yucatan Straits, but 

mechanisms by which they are dispersed 

into the Gulf of Mexico and southward 

to the coast of South America have not 

been determined. 

Glass Eel and Elver Staaes 

During the pelagic phase, leptocephali reach the size and physiological state at which they begin to 

metamorphose. The early stages of 

this transition involve a decrease in 

length and weight due to a reduction 

in water content, changes in the 

configuration of the head and jaws, 

and accelerated development of the 

digestive system (Fahay 1978). After 

these change; occur, the eels are 

similar in overall morphology to ye1 - 

low eels, but lack external pigmentation and are therefore called "glass 

eels." Glass eels actively migrate 

toward land and freshwater, and 

develop external pigmentation as they 

enter coastal areas. These small, 

pigmented eels are called "elvers ." 

The young eels begin migrating 

upstream before pigmentation is 

complete. Initially they are active 

at night and burrow or rest in deep 

water during the day (Deelder 1958). 

They typically move up into the water 

column on flood tides and return to 

the bottom during ebb tides (McCleave 

and Kleckner 1982; McCleave and 

Wippel hauser 1986). Similar behavior 

was reported for elvers at the mouth 

of the Indian River, Delaware, by 

Pacheco and Grant (1973), and for 

elvers of the European eel by Tesch 

(1977). The cues that trigger the 

change in behavior are not known, 

though Creutzberg (1959, 1961) showed 

that European glass eels were able to 

detect the odor of fresh water and 

alter their behavior accordingly. 

Sorensen (1986) showed that American 
eel elvers were strongly attracted to 

the odor of brook water and the odor 

of decaying leaf detritus and its 

associated microorganisms. Temperature gradient may also aid in the 

upstream orientation of glass eels 

(Tongiorgi et al. 1986). Glass eel5 

and elvers may delay upstream 

migration at the freshwater-saltwater 

interface whi 1 e behavioral ly and 

physiologically adjusting to the new 

environment (Sorensen and Eianchini 

1986). 

Most glass eels and elvers move 

into coastal areas, estuaries, and up 

freshwater rivers in late winter or 

early spring. Vladykov (1966) suggested that elvers generally arrive in 

southern estuaries earlier and ?t 

smaller sizes than in the north, but 

records indicate considerable over1 ap 

in the timing of shoreward movements 

along the Atlantic coast. In the 

Southeastern and Middle Atlantic 

States, migrating glass eels and 

elvers have been collected from Januat-y through Pay (Jeffries 1960; Smith 

1968; Fahay 1978; Hornberger 1978, 

cited by Sykes 1981; Sykes 1981; 

He1 fman et a1 . 1984a). 

Glass eels and elvers may reach 

New England estuaries as early as late 

winter (Jeffries 1960), but the main 

upstream migration is in spring. 

Glass eels have arrived at the coast 

of Maine from the end of March to 

about the third week of May (Dr. J. D. 

McCleave, University of Maine at 

Orono; pers. comm.). In Rhode Island 

the elver migration peaks during April 

and May (Haro 1986; Sorensen and 

Bianchini 1986), whereas in Maine the 

run is primarily from late April to 

June (Ricker and Squiers 1974; Sheldon 

1954). Most upstream migrating eels 

arriving in May at the freshwater 

interface in a Rhode Island brook were 

not completely pigmented, but most 

were fully pigmented by July (Sorensen 

and Bianchini 1986). In 1974 the run 

along the southern and central 

portions of the Maine coast was 

composed primarily of unpigmented 

glass eels for the first few weeks and 

almost entirely of pigmented elvers by 

the eighth week. 1 n northern coastal 

Maine the entire run was composed of 

glass eels. Smith and Saunders (1955) 

reported the arrival of elvers in 

Passzlmaquoddy Bay, New Brunswick, in 

late April. 

Sma 11 numbers of elvers regularly 

arrive in estuaries in the fall, and 

Fahay (1978) suggested that these 

"early" arrivals my be the earliest 

spawned individuals or a segivent of 

the main body of leptocephali that is 

mov~d northward rore quickly than most 

by localized water currents. kiternatively, these elvers may be "late" 

arrivals produced from leptccephal i 

that did not metam~rphose during the 

previous winter and spring. 

Elvers eventual ly begin swimming 

upstream and become most active during 

the day (Sorensen and Bianchini 1986). 

The onset of this active upstream 

migration may be triggered by changes 

in water chemistry caused by intrusion 

of estuarine water during high spring 

tides (Sorensen and Bianchini 1986). 

Tesch (1977) indicated that elvers of 

A. - anguilla orient to river currents 

for upstream movement; if the current 

becomes too weak or too strong (velocities not specified), the fish may 

move into backwater areas, severely 

delaying upstream progress. Basic 

similarities in behavior of European 

and American eel elvers suggest that 

those of American eels would be 

similarly affected by fast or slow 

river currents. 

Haro (1986) indicated that the 

main concentration of elvers in a 

coastal Rhode Island stream required 

about 1 month to move a distance of 

200 m ahove the tidal 7one, and that 

some American eels may continue migrating upstream as yellow eels of 

age I I or 01 der. The scarcity of 

small, younq eels in lakes that are 

far inland supports the idea of continued upstream migration by yellow 

eels (Hurley 1972; Facey and LaBar 
1981; Kolenosky and Hendry 1982). 

Eels ascending the eel ladder at the 

Moses-Saunders Dam on the St. Lawrence 

River at Cornwall, Ontario (approximately 1600 km from the ocean), were 

generally 3 to 8 years old (Liew 

1982). 

Yellow and Silver Eels 

Many investigators (e.g., Bigel ow 

and Schroeder 1953; Vladykov 1966) 

have stated that female yellow eels 

occur primarily in freshwater, and 

males generally in saltwater or 

brackish water. Dolan and Power 

(1977), however, after an extensive 

review of literature, concluded that 

this "female-freshwater, male-sal twater" theory was not supported. In a 

Georgia river, the percentage of 

sexually differentiated ye1 low eels 

that were males was 36 in the estuary 

and 6 in freshwater (Helfman et al. 

1984a). In the Cooper River system in 

South Carolina the percentages of 

males were 7 in saltwater (Fichener 

1980), 5 in brackish water (Hansen and 

Eversole 1984), and 3 in freshwater 

(Harrell and Loyacano 1980). Winn et 

al. (1975) reported higher percentages 

of males in freshwater and females in 

saltwater in Rhode Island streams and 

estuaries, but did not explain the 

methods used to determine sex. Dolan 

and Power (1977) indicated that 

histological examination of the gonads 

is necessary to determine sex in eels. 

Sexual differentiation does not 

occur until eels are about 200-250 mm 

long (Dolan and Power 1977). Before 

completion of the differentiat,ion 

process some eels have gonads containing male and female gametes 

(juvenile hemaphrodi tism; Tesch 1977), 

but after gender is established, it 

does not change (Fahay 1978). Differentiated and undifferentiated 

ye1 low eels may overlap considerably 

in size and age (Gray and Andrews 

1970; Dolan and Power 1977; Hansen and 

Eversole 1984; Helfman et a1 . 1984a). 

In addition to the possible 

freshwater-sal twater variation in the 

sex ratio, there seems to be geographic variation in the distribution 

of the sexes. Vladykov (1966) wrote 

that males predominate from New Jersey 

to Fl ori da, whereas females predomi nnate from New York to Newfoundland. 

Although work in South Carolina and 

Georgia did not support the idea that 

southern stocks are predominantly 

male, the percentage of males was 

higher than that reported in northern 

areas. Vladykov believed that a 

latitudinal change in sex composition 

was related to the size differences in 

elvers along the coast, and supposed 

that the smaller elvers entering 

southern streams become males and the 

1 arger elvers entering northern 

systems develop into females. The 

presumed geographic distribution of 

sex in the American eel may be a 

result of selectivity of sampling gear 

and the possible exclusion of smaller 

males in northern studies, plus the 

assumption that the geographjc distribution of sex in the American eel 

would parallel that demonstrated for 

the European eel (Dolan and Power 

1977). 

Limited evidence suggests that 

the gender of American eels is determined to some extent by environmental 

factors. Fahay (1978) wrote that the 

sex of the European eel can be 

environmentally influenced, but indicated that the factors responsible 

could only be speculated about. The 

1 ong developmental period in freshwater or brackish water in combination 

with juvenile hermaphroditism provides 

a setting in which environmental 

factors could regulate t.he gender of 

eel s . 

Male American eels tend to be 

more abundant in estuaries than in 

upriver sites, and more males have 

been found in Southeastern States than 

in ~orthern locations. One possible 

explanation is that male leptocephal i 

and elvers do not migrate as far as 

females, and hence remain in southerly 
or downstream areas. It is also possible that male eels prefer hioher 

salinities than females and move 

downstream to coastal areas after they 

are differentiated, but this behavioral pattern has not been observed 

and it would not explain the latitudinal trend. Ever1 where males have 

been found to be most abundant, in 

Georgia estuaries (Helfman et al. 

1984a), they are still outnumbered by 

females. 

The fact that American eels 

appear to be a single, panmictic 

population suggests that latitudinal 

variations in the sex ratio are not 

genetically determined but could be 

due to variations of environmental 

factors, such as food qua1 ity and 

population density (Fahay 1978). 

Parsons et al. (1977) believed that 

stocking of European eel elvers into 

Lough Neagh, Northern Ireland, led to 

a higher population density and a 

marked increase in the proportion of 

male eels that subsequently emigrated 

from the lake. Similarly, Egusa 

(1979) indicated that elvers of A. - anguiila and A. japonica grown in 

Ja~anese ~onds-under crowded condi - 

ti bns higher percentages of 

males than are found in wild populations, suggesting that variations in 

the sex ratio of anguillid eel populations may be related to pcpulation 

density. Sal ini ty apparently is not 

an important sex determinant; sex 

ratios were similar in the freshwater 

and brackish water cul ture ponds 

studied by Egusa. 

Growth rate, which is affected by 

temperature, food availabil i ty, and 

length of the growing season, might 

alsc be a factor in determining sex. 

This could result ir! different 1 ife 

history strategies for males and 

females (Helfman et al., in press). 

Eels that grow rapidly, such as those 

in highly productive southern 

estuaries, may have greater reproductive fitness if they are males. 

This is especially true if rapid 

growth resul ts in earl ier maturation 

(see Stearns and Crandall 1984). 

Large size would not be beneficial to 

male eels because small mature males 

can produce an abundance of gametes. 

However, the fecundity of female eels 

is highly dependent on size. Therefore, females that grow slower but 

reach larger sizes, such as those in 

northern and upriver 1 ocations, 

probably contribute more eggs to the 

next generation than do females that 

grow rapidly but mature at younger 

ages and smaller sizes, such as those 

in the southeastern United States. 

Natural selection would perpetuate 

such a system where the fastest 

growing eels tend to be males whereas 

eels that grow slower but get larger 

are females (Helfman et a1 . , in 

press). 

Eels are more active at night 

than during the day. Direct observation of yellow eels in a north Florida 

cave-spri ng indicated that eels 

changed behavior at dawn and dusk, 

when light levels were generally 

10-100 1 ux (He1 fman 1986). Laboratory 

studies have shown that silver eels 

are also pore active in darkness than 

in light, and that activity peaks 

during 1 ight-dark transition (Edel 

1975, 1979). Telemetry showed that 

yellow eels in a tidal creek were 

generally inactive during the day and 

active at night (Helfman et al. 1983). 

Activity was, however, influenced by 

tidal cycles with eels exhibiting 

greater activity during high tide. In 

a tidal cove studied in Maine, eels 

were moderately abundant in seine 

hauls at night but were never captured 

during the day (McCleave and Fried 

1975). Commercial harvest information 

also indicates that eels are more 

active at night (see Eales 1968; Tesch 

1977). 

Estimates of the home range of 

eels extend to 3.4 ha in small 

streams, tidal rivers, and tidal 

creeks (Gunning and Shoop 1962; 

Bianchini et al. 1982; Bozeman et al. 

1985); from 2.4 to 65.4 ha in a large 

lake (LaBar and Facey 1983); and < 100 
m along a tidal creek in summer in a 

Massachusetts salt varsh (Ford and 

Mercer 1986). Ford and Kercer 

suggested that large eels may 

establish territories in the wider 

marsh creeks, thus restricting small 

eels to narrower creeks at the back 

of the marsh. Pgonistic interactions 

in which large eels displace smaller 

eels have been reported el sewhere 

(He1 fman 1986). 

Eels begin the sp?wning migration 

in late summer and fall throughout 

much of New England and eastern 

Canada. Migration from lakes that are 

well in1ar;d may begin earlier. 

Catches of eels leaving Lake Champlain 

by way of the Richileau River were 

heaviest from June to August (R. 

Thuot , commerical fisherman, I berville, Quebec; pers. comm.). Eels 

seew to leave later in the Southeastern and Middle At1 antic United 

States than in New England States. 

This delay may function to synchronize 

arrival at the spawning grounds in the 

Sargassu Sea (Wenner 1973; Facey and 

He1 fman, ir! press). Many downstream 

migrating eels may not yet have 

developed the external characteristics 

associated with the migratory silver 

eel stage. Northern eels may begin 

migration at an earl ier dev~l opmental 

stage, perhaps to cowpensate for the 

longer time required to reach the 

spawning grounds (Wenner 1973). 

The metamorphosis from yellow eel 

to silver eel includes several physiological changes: (1) color change (to 

a metallic, bronze-black sheen; pectoral fins change from yellow-green to 

black); (2) fattening of the body; (3) 

thickening of the skin; (4) enlargement of the eyes and changes in visual 

pigments in the eye in preparation for 

migrating at greater ocean depths 

(Vladykov 1973; Beatty 1975); (5) 

increased length of capillaries in the 

rete of the swim bladder, which also 

may be an indication of migration at 

greater depths (Kleckner and Kruger 

1981); and (6) degeneration of the 

digestive tract. Silver (metamorphosed) eels appear to be better 

adapted to swimming than yellow eels 

(Holmberg and Saunders 1979). 

Few details are known about the 

oceanic spawning migration of the 

American eel. The first collecticns 

of adults in offshore waters were 

reported hy Wenner (1973) in the open 

ocean southeast of Cape Cod; east of 

Assateague Island, North Carolina; and 

southeast of Chesapeake Bay. The 

means by which eels locate the spawning grounds are poorly understood. 

Miles (1968) concluded that eels were 

capable of nonc~lestial orientation 

(southward), arc! Rommel and Stasko 

(1973) indicated that eels may use 

geoelectric fie1 ds generated by ocean 

currents for orientation. Robins et 

al. (1979) photographed two adult 

Anguilla eels on the floor of the 

Atlantic Ocean in the Bahamas at 

depths of about 2000 m, and a1 though 

it was impossible tc identify the 

species, the authors be1 ieved the 

specimens to bp prespawni~g - A. 

rostrata. 

Stasko and Rommel (19771, who 

tracked five migrating eels, in the 

lower St. Croix River estuary, New 

Brunswick, Canada, reported that one 

eel moved 25 km in 20 h and another 

moved 38 km in 40 h. The eels they 

studied showed considerable vertical 

movements in the water column; 

behavior did not change with die1 or 

tidal cycles. Edel (1976) be1 ieved 

that the depth at which American eels 

migrate in the ocean varied with light 

intensity, and that swimming depth 

varied with turbidity of the water. 

GROWTH CHARACTERISTICS 

Fcr the American eel the length 

at hatching is not known; however, the 

J?panese eel hatches at about 2.7 mm 

(Yamamoto and Yavauchi 1974). Growth 

rate of American eel leptocephal i has 

been estimated to be 0.243 ~ni/day 

(Wi ppel hauser et a1 . 1985). Larvae 
typically reach 40 to 70 mm after 1 

year. The metamorphosis from planktonic larva to the upstream migrating 

form is accompanied by a decrease in 

length and weight due to reduction in 

water content of the body. Glass eels 

captured while migrating upstream in 

late February in Georgia were 49-56 mm 

long and 250-300 days old (Helfman et 

al. 1984a). The length of glass eels 

c o l l e c t e d from January through April 

in South Carolina averaged 55 mm long 

and ranged from 45 to 65 mm (Hornberger et al. 1978). Ricker and 

Squiers (1974) reported that glass 

eels and elvers caught along the coast 

of Maine from late April through the 

end of June averaged 59.2 mm (95% 

confidence interval , 57.5-60.8 mm) . Elvers grow slowly, reaching about 127 

mm after the first year in freshwater 

(Bigel ow and Schroeder 1953). Ye1 1 ow 

eels typically grow slowly but reach 

weights up to 6.8 kg; females caught 

from the St. Lawrence River were 960 

to 1,270 mm in length and weighed 0.9 

to 4.5 kg (Fahay 1978). Females grow 

to a larger size than males. 

Eels have been aged from otoliths 

and scales. ' Otoliths in eels consist 

of a translucent nucleus (formed at 

sea), surrounded by broad opaque 

summer zones and narrow translucent 

winter zones (Gray and Andrews 1971). 

Eels in Canadian waters formed their 

first scales at 160 to 200 mm during 

their third to fifth year of life, and 

annual rings were formed on the scales 

in subsequent winters (Smith and 

Saunders 1955). Thus, in northerly 

areas, age in years generally is the 

number of scale rings plus three. 

However, because scales continue to 

form as the eel grows, different 

scales from the same fish yield 

different ages (Smith and Saunders 

1955). Although otoliths may show 

more than one opaque ring in a year 

(Dee1 der 1976), they are preferred for 

estimating the age of eels. 

Growth rates within year classes 

are highly variable, leading to 

considerable variation in length at 

age and poor predictability of age 

from size. Lengths of eels at various 

ages in northern locales are summarized in Table 1. Eels in the Southeastern United States seem to mature 

at younger ages and smaller sizes and 

therefore may not get as large as 

northern eels (He1 fman et a1 . 1984a). 

The great variability in length 

within an age class makes it virtually 

impossible to accurately estimate eel 

growth rates from length-age regressions. Perhaps the best way to determine growth rates is to monitor 

individuals during long-term tagging 

studies. Helfman et al. (1984b) compared growth rates estimated from 

length-age analysis to measured growth 

rates of tagged eels (initial size: 

275-475 mm) in a Georgia estuary. On 

the basis of indirect reasurements 

(1 ength-age regression and meanlength-at-age analysis), estimated 

annual growth rates were 44 mmlyear, 

whereas independent direct measurements (seasonal summation and 1 ongterm recaptures) yielded values of 57 

and 62 mmlyear. Gunning and Shoop 

(1962) reported that four recaptured 

eels (initial lengths, 255-915 mm) in 

Louisiana streams grew an average of 

140 mmlyear (range, 46-325 mmlyear). 

In Massachusetts sal t marshes, 

Haedrich and Pol loni (1978) showed 

that eels averaging 52 cm long grew 

about 4% per year, and Polloni et al. 

(1980) reported that eels 500-700 mm 

long grew about 6% (range, 4.1-8.4%). 

The lengths of 10 eels tagged in 1979 

and recaptured in 1986 in Vermont 

waters of Lake Champlain increased an 

average of 9.7 cm over the 7-year 

period (Dr. G. W. LaBar, University of 

Vermont, Burl ington; pers. comm.) . 

COMMERCIAL AND SPORT FISHERIES 

The European market has been the 

major outlet for U.S. landings of 

yellow and silver eels (Fahay 1978). 

Eels are hardy and can be densely 

packed and shipped alive if they are 
Table 1. Total lengths (cm) of American eels at various ages in different 

local ities. 

Local i ty 

NewAge founi- New Rhode New Delawa e South 

group land 6runswickb OntarioC vermontd 1slande Jerseyf F?iver6 Carolina 

I 

I I 16-19 

I11 21-23 

I V 23-30 

V 25-40 

V I 29-46 

VII 36-50 

VIII 43-59 

I X 49-66 

X 60-78 

XI 66-84 

XI1 75-77 

XI11 

XI V 

X V 

XV I 

XVI I 

XVIII 

XIX 

X X 

XX I 

XXII 

XXIII 

a~ray and Andrews 1971. 

b~mith and Saunders 1955. Ages estimated by adding 3 years to the number of 

scale rings counted by authors. 

Ctlurley 1972. 

d~acey 1980. 

e6ieder 1971. 

fogden 1970 

g~ohnson 19j4. 

h~ansen and Eversole 1984. Ages estimated by adding 1 yeer to the number 

of inland years reported by authors. 
kept moist, cool, and supplied with 

oxygen. A1 though 1 ive eels are 

preferred in Europe, many are shipped 

frozen . 

Commercial fishermen use a variety of methods to catch eels, including lift nets, drift nets, traps, 

weirs, otter trawls, pound nets, fyke 

nets, spears, hand1 ines, eel pots, and 

haul seines (Fahay 1978). Yellow eels 

in freshwater or brackish water are 

taken primarily with baited traps or 

eel pots. 

A summary of catch statistics 

along the Atlantic coast from 1955 to 

1973 showed that landings from the 

Middle Atlantic (New Jersey to 

Virginia) consistently exceeded those 

from the North Atlantic (Maine to New 

York) and South Atlantic (North Carol ina to Florida) (Fahay 1978). From 

1970 to 1973, the annual North 

At1 antic harvest averaged 125,4-18 kg, 

with an average value of $84,000. In 

1977 the eel landings for Maine, New 

Hampshire, and Massachusetts were 

about 79,700, 2,700, and 143,300 kg, 

valued at $263,000, $5,000, and 

$173,000, respectively (U.S. Department of Commerce 1984). Massachusetts 

landings were about 100,300 kg in 

1978 and 81,800 kg in 1979 (U.S. 

Department of Commerce 1980a), and 

Maine landings were about 60,500 kg 

in 1978 and 50,400 kg in 1979 (U.S. 

Department of Commerce 1980b). By 

1985 the Massachusetts catch was less 

than 3,800 kg (E.D. Hubbard, Massachusetts Division of Marine Fisheries; 

pers. comm.). Landings in Maine and 

Massachusetts in 1980-85 are shown in 

Table 2. Some of the landing statistics may be inaccurate. 

A1 though U.S. eel harvests seemed 

to be increasing through the 19701s, 

eel fishing in New England has 

decl ined drastically in recent years. 

The situation may be due to reasons 

cited by E. D. Hubbard, in her 

assessment of the Massachusetts eel 

fishery (pers. comm., June 1986). 

Tab1 e 2. Prel imi nary commercial 

fishery landings of eels in Maine and 

Massachusetts, 1980-1985~. (Information provided by R. Schultz, Resource 

Statistics Division, National Marine 

Fisheries Service). 

- Maine Massachusetts 

Year weight value weight value 

(kq) (kg) 

a~oes not include 9 kg reported in New 

Hampshire in 1981. 

"During the years from roughly 

1975 to 1980 the estuarine eel fishery 

grew considerably in Massachusetts, 

principally on Cape Cod, south of 

Boston and in southeastern Massachusetts coastal towns. Numbers of men 

fishing increased as well as the total 

landings, although accurate statistics 

are lacking. This was due to the high 

ex-vessel prices paid to fishermen, 

the result of renewed interest and an 

ever-increasing European eel demand. 

Whereas nearly every European country 

consumes eel s, apparent1 y 1 ocal 

supplies could not meet the total 

demand and so North American exports 

began to fill this gap. 

"Somewhat abruptly in 1981 most 

of these U.S. export markets plummeted due to a number of factors, but 

principally due to the very tight 

economic situation in the U.S. as well 

as abroad. Other contributing factors 

were contaminated shipments of eels 

from Canada and grading (1 ive eels) 
problems. Exports of all finfish have 

sl umped over the 1 astseveral years 

due to an inflationary U.S. dollar. 

During this time, the Europeans 

imported eels from new sources across 

the Pacific. 

"Several well established eel 

buyers along the American East Coast 

closed their doors during 1982, [primarily due] to high shipping costs and 

inflated exchange rates. Because buyers were not interested in eels, or at 

much lower prices, very few persons 

fished during 1982, continuing through 

to the present. The last major buyer/ 

exporter in Massachusetts ceased his 

eel operations in 1985. With unfavorable market conditions continuing in 

Europe over the last 4 to 5 years, the 

coastal eel fishery here in Massachusetts has been practically nonexistent. In the fall months, the traditional Christmas eel demand in the 

larger U.S. cities means a shortterm, high priced market for fishermen. But other than scattered and 

seasonal ly 1 i m i t e d sales demand, 

fishermen have not set their pots, 

a1 though the interest is very high. 

One buyer in Maine is doing business 

with some of the local fishermen and 

another company in New Hampshire has 

very recently expressed interest in 

exporting eel s ." 

It is possible, however, that 

European demand for American eels may 

increase in the late 1980's because of 

the accidental release of toxic 

chemicals into the upper Rhine River 

in fall 1986; hundreds of thousands of 

European eels were killed. If the 

accident significantly affects 

European eel fisheries for many years, 

an increased demand for American eels 

might extend into the 1990's. 

A fishery for European eel elvers 

began in Europe during the late 1960's 

to supply Japan's demand for young 

eels to use in pond culture. Elvers 

were packed 1 ive in boxes and shipped 

to Japan, where prices paid for local 

- A. japonica elvers were $7/kg in 

1965-68, $300/kg in 1969, and $330 to 

$925/kg in 1971-73 (Fahay 1978; Egusa 

1979). Prices paid for European eel 

elvers in Japan initially were 

equivalent to those paid for local 

elvers, but European eel s were 

inferior in the pond culture systems 

because of poor growth and disease 

problems; in 1973, the Japanese paid 

only $30 to $50/kg for European elvers 

(Egusa 1979). 

Reports of $100 to $2,000 per kg 

attracted some Maine fishermen into 

the elver market, but they found that 

these reports were inflated over the 

actual value of a successful shipment 

(Ricker and Squiers 1974). Elvers 

vary widely in size, and the number 

per kilogram may range from about 

2,200 to more than 12,000 (Ricker and 

Squiers 1974). She1 don ( 1974) 

reported locations and techniques for 

catching, holding, and transporting 

elvers in Maine. In Maine, elver 

landings were 10 metric tons in 1977 

and 7.6 in 1978, valued at $110,000 

and $63,251 (Dow 1982). Massachusetts 

prohibits harvesting of elvers except 

for aquaculture purposes, for which a 

permit is required. From 1978 to 1986 

only one such permit was requested and 

issued (E.D. Hubbard; pers. comm.). 

The Japanese Elver Culture Association 

began assessing the performance of 

Maine elvers in the mid 1970's. There 

have been reports that the elvers of 

the American eel did not thrive and 

that the Japanese eel culture industry 

began buying A. japonica elvers from 

China (L. Flagg, Maine Department of 

Marine Resources; pers. comm. ) . 

The feasi bi 1 i ty of commercial 

"grow-out" operations in North 

Carolina was assessed by Easley and 

Freund (1977). Interest in culturing 

was stimulated by rising prices during 

the late 1960's and early 19701s, but 

considerable refinement of techniques 

was needed. Development of eel aquaculture has focused on methods for 

collecting elvers and on physical 

features of grow-out systems. Hormone 

injections can be used to induce 
maturation of female American eels 

(Edel 1976), but proper spawning 

conditions are unknown, and eel culture remains dependent on capturing 

wild elvers. Hinton and Eversole 

(1978, 1979, 1980) evaluated the toxic 

effects of chemicals commonly used in 

aquaculture on glass eels (mean 

length, 55 mm), elvers (mean length, 

97 mm) , and ye1 1 ow eel s c o l l e c t e d from 

South Carolina rivers. Lower temperatures and the shorter growing 

season might make commercial culturing 

of eels less practical at northern 

latitudes. 

Restrictions on eel harvest vary 

among the North Atlantic states. In 

Maine the size of catch is not 

regulated, but certain permits and 

regulations pertain to some towns and 

rivers (Ricker 1976). Commercial 

fishing licenses are issued by the 

Department of Marine Resources, or by 

the Department of Inland Fisheries and 

Wildlife (for inland waters). The 

Department of Marine Resources also 

issues licenses for anyone buying or 

selling eels in the wholesale trade. 

In Massachusetts, coastal towns 

regulate commercial eel fishing in 

saltwater and estuaries (Amaral 1982; 

E.D. Hubbard; pers. comm.). Only eels 

102 mm (4 inches) long or longer may 

be harvested, and only by nets, pots, 

spears and angl ing . Commercial 

fishing for eels is permitted in 

inland waters, but a permit and 

fishing 1 icense are required. Only 

eel pots with a mesh no less than 13 

mm (0.5 inch) and a funnel openina not 

greater than 51 mm (2 inches) may be 

used. Fishermen are required to keep 

daily logs, and no eels less than 102 

mm long may be taken. The Division of 

Marine Fisheries issues the licenses 

required to sell eels. New Hampshire 

also prohibits the taking of eels less 

than 102 mm long (T. Spurr, New Hampshire Fish and Game Department, 

Concord; pers. comm. ) . 

Population size and biomass 

estimates of American eels are scarce 

and vary widely. Bianchini et a1 . 

(1982, cited by Bozeman et a1 . 1985) 

estimated eel biomass at 75 kg/ha in 

the tidal section of a Rhode Island 

river. Bozeman et al. (1985) reported 

about 13 kg/ha in a Georgia tidal 

creek. A 600-111 section of a marsh 

creek in Massachusetts was estimated 

to contain about 350 yellow eels, a 

stock density equivalent to 875 eels/ 

ha (Ford and Mercer 1986). Standing 

crops up to about 80 kg/ha were 

reported in lakes in New Brunswick, 

Nova Scotia, and Prince Edward Island 

(Smith and Saunders 1955). The eel 

biomass in Coleback Lake, Maine, was 

about 50 kg/ha (Rupp and DeRoche 

1965), whereas estimates in shall ow 

(<2 m) portions of Lake Champlain, 

Vermont, were 161 to 421 kg/ha (LaBar 

and Facey 1983). The biomass estimates in Lake Champlain may have been 

high because there had been no commercial eel fishery on the lake before 

the study. 

Estimates of mortality or other 

vital statistics of eel stocks generally have not been reported, and 

factors regulating survival or stock 

size have not been evaluated. Helfman 

(unpubl. MS.l) suggested that the 

eel's long l i f e i n freshwater may make 

the stocks prone to local overharvest. 

Keefe (1982) suggested that declines 

in catch of eels per unit of fishing 

effort in North Carolina indicated 

overharvest. Because all American 

eels spawn in the Sargasso Sea, and 

there are apparently no genetically 

distinct stocks or subpopulations 

(Koehn and Williams 1978; Avise et al. 

1986), overharvest in one region could 

affect recruitment in other regions. 

Kolenosky and Hendry (1982) suggested 

taking a conservative approach to the 

harvesting of eels in Canadian waters 

'~evel opment and expansion of the 

fishery for American eels in Georgia. 

G.S. He1 fman, Department of Zoo1 ogy , University of Georgia, Athens, GA 

30602. Project summary, University 

of Georgia Sea Grant Program, 1983. 
of Lake Ontario, partly because of the 

declining catch per unit of effort. 

Nevertheless, some management policies 

allow or encourage locally heavy 

exploitation of migrating silver eels 

or elvers under the assumption that 

the numbers of elvers returning in 

later years will be maintained by 

escapement of spawning stock from 

other areas. 

American eels are caught by sport 

fishermen along the entire east coast 

of the United States. The estimated 

catch in 1979 by marine and estuarine 

recreational fishermen was 113,000 

eels in the North Atlantic States, 

172,000 in the Vlid Atlantic, 47,000 in 

the South Atlantic, and 43,000 in the 

Gulf coast region (U.S. Department of 

Commerce 1981). 

ECOLOGICAL ROLE 

Ye1 low eels are nocturnal, and a 

significant amount of their feeding is 

at night (Helfman 1986). They probably depend more on scent than on 

sight to locate food (Fahay 1978). 

The diet is diverse and generally 

includes nearly all types of aquatic 

fauna that occupy the same habitats. 

Eels swallow some types of prey whole, 

but also can tear pieces from large 

dead fish, crabs, or other items. 

Helfman and Clark (1986) documented 

the ability of eels to grasp large 

food items and spin rapidly to tear 

away pieces. Eels in freshwater feed 

on insects, worms, crayfish and other 

crustaceans, frogs, and fishes. 

Elvers collected from the Cooper 

River, South Carolina, ate aquatic 

insects (mainly larval and adult 

chironomids) , cladocerans, amphi pods, 

and fish parts (McCord 1977). The 

diet of yellow eels from the Cooper 

River varied with eel size and season. 

More types of food were eaten by 

intermediate-sized eels than by elvers 

or maturing eels; fish occurred in the 

diet primarily in winter and spring, 

whereas insects and mollusks were 

eat.en from spring through fall. 

Crustaceans, bivalves , and polychaetes 

were the major prey of eels in lower 

Chesapeake Bay; blue crabs 

(Call inectes sa idus) and soft-she1 1 

clams (Mya arenaria -? were significant 

prey (Wenner and Musick 1975). Eels 

shorter than 40 cm in New Jersey 

streams ate mainly aquatic insects 

whereas larger eels fed mostly on 

fishes and crustaceans (Ogden 1970). 

Most fishes eaten were bottom dwellers, reflecting the tendency of eels 

to feed near the bottom. In Vermont 

waters of Lake Champlain, eels ate 

primarily insects, crayfish, and 

fishes; larger eels (2 58 cm) ate more 

crayfish and fishes than did smaller 

eels (Facey and LaBar 1981). Eels 

have been considered significant 

predators on young saltnonids, but this 

is not well supported by the 1 iterature. In New Brunswick streams, only 

G of 300 eels with food in their 

stomachs had eaten salmonids (Godfrey 

1957). Of 4,340 European eels 

examined from six Welsh rivers, Sinha 

and Jones (1967) fou~d only 10 that 

had eaten salmonids. 

Little has been pub1 ished about 

predation on eels. Hornberger et al. 

(1978) reported that elvers and small 

ye1 1 ow eel s were eaten by 1 argemouth 

bass and striped bass in the Cooper 

River, South Carolina, but that eels 

were never a major component of these 

predators ' diets. Leptocephal i , glass 

eels, elvers, and small yellow eels 

probably are eaten by a variety of 

predatory f i shes. Sorensen and 

Bianchini (1986) stated that older 

eels eat incoming glass eels and 

elvers. Grown eels are eaten by 

species of eels other than 

anguillids and by qylls, bald eagles 

(~al iaeetus 1eucoceP~a~us), and other 

fish-eating birds Sinha and Jones 

Crane and Eversole (1980) found 

no parasites on glass eels migrating 

into the Cooper River, South Carolina, 

but examinations of elvers yielded 

four genera of protozoans (Tri chcdi na , 
Ichth o hthirius, Myxidium, and 

one species of 

mon0genet.i~ trematode (Gyroda;;;;~; 

angui 11 ae) . Crane and Eversol e 

reported that 214 of 218 yellow eels 

col lected from brackish waters of the 

Cooper River, South Carolina, were 

parasitized by 1 or more of 22 

helminth species. About 48% of yellow 

eels col 1 ected from brackish portions 

of the Cooper River were infested with 

one or rore ectoparasitic species from 

the classes Monogenea and Crustacea 

(Crane and Eversole, in press). 

Levels of parasitism by Ergasilus 

cerastes and E. celestis varied 

seasonally and Gth size and age of 

the host. Parasites of American eels 

in Quebec included protozoans, 

trematodes, nematcdes, cestodes, and 

copepods (Hanek and Mol nar 1974). The 

myxosporidian prctozoan Myxi dium 

zelandicum has been found in the kidneys and on the gills of the American 

eel (Komourdjian et a1 . 1977). 

ENVIRONMENTAL REQUIREMENTS 

Temperature 

The eel 's broad geographic range 

and diverse habitats suggest flexible 

temperature requiremerts. El vers and 

yellow eels live in waters ranging 

from cold, high-elevation or high1 ati tude freshwater streams and 1 akes 

to warm, brackish coastal bays and 

estuaries in the Gulf of Fexico. 

Jeffries (1960) found elvers at temperatures as low as -0.8 "C. 

Barila and Stauffer (1980) 

acclimated yellow eels to a range of 

temperatures between 6 and 30 "C and 

then measured preferred temperatures. 

Although preferred temperatures tended 

to increase with increased acclimation 

temperature, group differences were 

not significant, and the authors 

reported a final mean temperature 

preference of 16.7 "C. Karl sson et 

al. (1984) disagreed with the techniques and interpretation of Bari 1 a 

a~d Stauffer (1980), and claimed that 

acclimation temperature does influence 

preferred temperature. They found a 

final temperature preferendum of 17.4 

+ 2.0 "C (95% confidence interval). 

Marcy (1973) reported that American 

eels survived passage through the 

cooling system of a nuclear power 

plant, during which they were exposed 

to elevated temperatures for 1-1.5 hr. 

Poluhowich (1972) suggested that the 

American eel 's mu1 tip1 e types of hemoglobins serve to maintain a nearly 

ccnstant blood oxygen affinity when 

the eel is exposed to temperature 

changes. American eels accl imated at 

10 to 20 "C fed regularly and 

exhibited compensatory adjustments in 

oxygen consumpti on characteristic of 

many ectotherms (Walsh et al. 1983). 

However, acclimation to temperatures 

5 5 "C for over 5 weeks resulted in 

cessation of feeding and a dramatic 

decrease in oxygen consumption. 

Salinity 

The mechanisms by which glass 

eels or elvers orient during their 

shoreward migration have not been 

described. Eels are known for their 

extremely sensitive sense of smell, 

and olfaction may play a role in the 

ability of elvers to locate freshwater 

(She1 don 1974; Sorensen and Bianchini 

1986; Sorensen, 1986). European glass 

eel s and el vers become positively 

rhectactic when they first encounter 

freshwater that is mixed with seawater 

(Tesch 1977). A1 terations of patterns 

or magnitudes of freshwater inflows to 

bays or estuaries could alter flow 

regimes and thereby affect the size, 

timing, and spatial patterns of 

upstream migrations by elvers. 

Like temperature requirements , salinity requirements of postlarval 

eels can be inferred as being broad 

from the fact that the postlarval eels 

occur throughout a gradient of strictly fresh to brackish waters. Elvers 

do appear to delay upstream migration 

at the freshwater interface, however, 

perhaps to permit physiological 
adaptation to the new environment 

(Sorensen and Bianchini 1986). Leptocephal i are in near-ionic equilibrium 

with sea water (Hulet et a1 . 1972), 

but the osmolal ity of glass eels and 

elvers has not been reported. 

Dissolved Oxygen 

Dissolved oxygen requirements 

have not been thoroughly documented, 

but eels generally select water with 

high oxygen tension (Hill 1969). 

Elvers are sensitive to low oxygen, 

and should be held and transported in 

water with an oxygen concentration of 

at least 11 ppm (Sheldon 1974). 

Because elvers can absorb oxygen 

through the skin, they can better be 

transported damp and in air than in 

poorly oxygenated water. Evidently 

this is also true of adult eels. 

Tesch (1977) wrote that, "The capacity 

of the adult eel to survive in both 

air and water is associated with its 

ability to use both branchial and 

cutaneous modes of respiratory gas 

exchange. The eel survives better in 

air than in poorly oxygenated or 

polluted water ...." 

Habitat Structure 

Postlarval eels tend to be bottom 

dwellers and hide in burrows, tubes, 

snags, plant masses, other types of 

shelter, or the substrate itself 

( Fahay 1978). This behavior is 

reflected in their food habits, 

protects them from predators, and 

i nf 1 uences comrnerci a1 fishing 

techniques. Few other freshwater 

fishes display similar habitat use; 

int.erspecific competition fcr living 

space may therefore be limited. The 

presence of soft, undisturbed bottom 

sediments is important to migratin 

elvers as she1 ter. Edel (19793 

indicated that eels in his experimental systems were less active when 

shelter was present than when it was 

lacking. Vladykov (1955, cited by 

Fahay 1978) reported that adult eels 

in northern habitats lie dormant in 

the bottom mud during winter. 

River and Tidal Currents 

The glass eel's and elver's 

nocturnal activity and re1 iance on 

tides for upstream movement have 

a1 ready been mentioned. Flow 

a1 teration in estuaries might affect 

upstream migration of small eels. 

Dams and other obstructions probably inhibit migrating elvers (Tesch 

1977), and 1 imi t recruitment to 

upstream sites; however, eel s can 

travel over wet vertical surfaces such 

as dams. 

Tides and the time of day 

affected movements of yellow eels in 

a tidal creek in Georgia (Helfman et 

al. 1983). Movements of eight 

telemetered eels were restricted to 

the main creek channel during the day, 

but at night the fish were near the 

mouths of feeder creeks at low tide or 

in flooded marsh areas during high 

tide. Helfman et al. (1983) termed 

this movement "a nocturnal activity 

pattern modified by tidal flow," and 

suggested that such movements were 

foraging trips. 

Contaminants 

Little work has been done on 

toxic effects of pollutants or the 

to1 erance 1 imi ts in American eels. 

Tolerance would be expected to vary 

with developmental phase, and the 

eel's long residence in freshwater 

rivers could lead to repeated doses of 

toxicants and accumulation of toxic 

1 eve1 s (Holmberg and Saunders 1979). 

Work done by Hinton and Eversole 

(1978, 1979, 1980) on toxicity of 

aquacul tural chemicals to various 1 ife 

stages of eels suggested that 

to1 erance to chemicals increases with 

size or age. 

In September 1976 the New York 

State Department of Environmental 

Conservation and the Department of 
Health banned the possession and sale eels (Blake 1982). This ended the 

of eels taken from the Hudson River Hudson River fishery for eels. Jn 

and Lake Ontario because levels of 1978 the restrictions were modified to 

polychl ~robi phe~yl s (PCBs) exceeded a1 1 ow sales of Lake Ontario eels t,o 

the C.S. legal maximum level of 2 ppm: foreign markets, which apparent1 y 

they were 50-75 ppm in Hudson River permit higher PCB concentrations than 

eels and 2.5-4.5 ppm in Lake Ontario are allowed in the United States. 

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RWRT OOCUMENTATlON 1. REWm No- L 

PAGE 1 Biological Report 82(11.14)* 1 

Species Profiles: Life Histories and Environmental Requirements 

of Coastal Fishes and Invertebrates (North Atlanti c)--American Eel 

*U.S. Army Corps of Engineers Report No. TR EL-82-4 

I6 Abstnst (Lirnlt: 200 word.) 

7. hmmia) 

Douglas E. Facey and Michael J. Van Den Avyle 

b. h~+~mlry ~~~.ntzat~on ~erm and ~naa 

Georgia Cooperative Fish and Wildlife Research Unit 

School of Forest Resources 

University of Georgia 

Athens, GA 30602 

12. Swnwdna Oqmnlzatlon Nmrne and Addnaa 

Species profiles are 1 iterature summaries of taxonomy, 1 i fe history, and environmental 

requirements of coastal fishes and aquatic invertebrates. They are prepared to assist 

with impact assessments. The American eel is an ecologically and economically important 

catadromous species that occupies freshwater streams, rivers, brackish estuaries, and 

the open ocean during various phases of its life cycle. Adult eels apparently spawn in 

the Sargasso Sea, and ocean currents transport the developing larvae northward until the 

young metamorphose into juveniles capable of swimming shoreward and moving upstream into 

coastal areas, estuaries, and rivers. Developing eels commonly remain in freshwater or 

brackish areas for 10-12 years before migrating to spawn. American eels tend to be 

bottom-dwellers and feed on a variety of fauna that occupy the same habitats. Eels 

occupy areas having wide ranges of temperature, sal inity, and other environmental 

factors, suggesting broad tolerance limits, but few studies of requirements have been 

reported. Salinity patterns and water currents created by river discharges into coastal 

areas apparently provide the gradient that cues shoreward migration of juvenile eels. 

Alteration of patterns of freshwater inflows to estuaries and bays could affect 

upstream migrations. 

a Pmdomlry Oqmnlzatlon ~mpt. N 

10. hoj.~nmak/~orh Untt NO. 

11. bmnct(C) or Grmnt(G1 No. 

(0 

(Q 

17. Documnt Anmiysia m. Deudpton 

Estuaries Life cycles Contaminants 

Fisheries Growth Animal migrations 

Salinity Oxygen Aquaculture 

Temperatures 

National Wetlands Research Center U. S. Army Corps of Engineers 

Fish and Wildlife Service Waterways Experiment Station 

U.S. Department of the Interior P.O. Box 631 

Washington, DC 20240 Vicksburg, MS 39180 

Anguilla rostrata 

Catadromous fishes 

Life history 

Environmental requirements 

c. COSATI flmld/Gmup 

.a Avmllablllty Stmtmrnmnt 1 19. Sccuritv Class (This RewrO I 21. No. of Paaea 

Unlimited distribution 28 

) 9. Pdce 

I Unclassified ee ANSI439.18) OPTIONAL FORM 272 lC7i 
As the Nation's principal conservation agency, the Department of 

the Interior has responsibility for most of our nationally owned 

public lands and natural resources. This includes fostering the 

wisest use of our land and water resources, protecting our fish 

and wildlife, preserving the environmental and cultural values of our 

national parks and historical places, and providing for the enjoyment of life through outdoor recreation. The Department assesses 

our energy and mineral resources and works to assure that their 

development is in the best interests of all our people. The Department also has a major responsibility for American Indian reservation 

communities and for people who live in island territories under U.S. 

administration. 

U.S. DEPARTMENT OF THE INTERIOR 

FlSH AND WII-DLIFE SERVICE 

TAKE PRIDE 

in America 

UNITED STATES 

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FlSH AND WILDLIFE SERVICE 

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