ML072060550
| ML072060550 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 08/01/1987 |
| From: | Cordes C, Facey D, Moran D, Vandenavyle M Univ of Georgia, US Dept of Interior, Fish & Wildlife Service, US Dept of the Army, Corps of Engineers |
| To: | Office of Nuclear Reactor Regulation |
| Davis J NRR/DLR/REBB, 415-3835 | |
| Shared Package | |
| ML072060321 | List:
|
| References | |
| TR EL-82-4 82(11.74) | |
| Download: ML072060550 (36) | |
Text
REVPPRE%1C COPY Do Not Remove from the Library U. S. Fish and Wildlife Service
...... I Wvlurjus Kesearch Center TR EL-82-4 Biological Report 82 (11.74) 700 Cajun Dome Boulevard August 1987 Lafayette, Louisiana 70506 Species Profiles: Life Histories and Environmental Requirements of Coastal Fishes and Invertebrates (North Atlantic)
AMERICAN EEL Coastal Ecology Group Fish and Wildlife Service Waterways Experiment Station U.S. Department of the Interior U.S. Army Corps of Enaineers w
- V C~VL
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 by 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 Wetlands Research Center 1010 Gause Boulevard Slidell, 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 Research 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 coastal 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, life history, ecological role, environmental requirements, and economic importance, if applicable. 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 following addresses.
Information Transfer Specialist National Coastal Ecosystems Team U.S. Fish and Wildlife Service NASA-Slidell Computer Complex 1010 Gause Boulevard Slidell, LA 70458 or U.S. Army Engineer Waterways Experiment Station Attention: WESER-C Post Office Box 631 Vicksburg, MS 39180 iii
CONVERSION TABLE Metric to U.S. Customary Multiply B03 To Obtain millimeters (mm) 0.03937 inches centimeters (cm) 0.3937 inches meters (m) 3.281 feet meters (m) 0.5468 fathoms kilometers (km) 0.6214 statute miles kilometers (km) 0.5396 nautical miles 2
square meters (m ) 10.76 square feet square kilometers (km2 ) 0.3861 square miles hectares (ha) 2.471 acres liters (1) 3 0.2642 gallons cubic meters (m 3
) 35.31 cubic feet cubic meters (m ) 0.0008110 acre-feet.
milligrams (mg) 0.00003527 ounces grams (g) 0.03527 ounces kilograms (kg) 2.205 pounds metric tons (t) 2205.0 pounds metric tons (t) 1.102 short tons kilocalories (kcal) 3.968 British thermal units Celsius degrees (°C) 1.8(°C) + 32 Fahrenheit degrees U.S. Customary to Metric inches 25.40 millimeters inches 2.54 centimeters feet (ft) 0.3048 meters fathoms 1.829 meters statute miles (mi) 1.609 kilometers nautical miles (nmi) 1.852 kilometers square feet (ft 2 ) 0.0929 square meters square miles (mi 2 ) 2.590 square kilometers acres 0.4047 hectares gallons (gal) 3.785 liters 3
cubic feet (ft ) 0.02831 cubic meters acre-feet 1233.0 cubic meters ounces (oz) 28350.0 milligrams ounces (oz) 28.35 grams pounds (lb) 0.4536 kilograms pounds (lb) 0.00045 metric tons short tons (ton) 0.9072 metric tons British thermal units (Btu) 0.2520 kilocalories Fahrenheit degrees ('F) 0.5556 (-F - 32) Celsius degrees iv
CONTENTS Page PREFACE .............................................................. ii CONVERSION TABLE .......................................................... iv ACKNOWLEDGMENTS ........................................................... vi NOMENCLATURE/TAXONOMY/RANGE.. ............................................
MORPHOLOGY/IDENTIFICATION AIDS .............................................. 3 REASON FOR INCLUSION IN.SERIES .............................................. 3 LIFE HISTORY ............................................................... 4 Spawning .................................................................. 4 Larval (Leptocephalus) 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 V
ACKNOWLEDGMENTS We gratefully acknowledge the helpful comments and criticisms of Gene S. Helf-man of the University of Georgia, Elizabeth D. Hubbard of the Massachusetts Division of Marine Fisheries, George W. LaBar of the University of Vermont, James 0. 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.
vi
Figure 1. American eel.
AMERICAN EEL NOMENCLATURE/TAXONOMY/RANGE into the Gulf of Mexico as far as Tampico, Mexico, and in Panama, the Scientific name ...... Anguilla rostrata Greater and Lesser Antilles, and Preferred common name ......... me--rican southward to the northern portion of eel (Figure 1) the east coast of South America Other common names ........... Anguille, (Tesch 1977). The species is yellow eel, green eel, black eel, abundant in the North Atlantic little eel, bronze eel, glass eel, states (Figure 2), the eastern silver eel, river eel Canadian provinces, and southward to Class ..................... Osteichthyes Mexico; it is resident in the Order ................... Anguilliformes Mississippi Valley, and occurs in Family ..................... Anguillidae the West Indies and Bermuda. Bertin (1956) reported the latitudinal Geographic range: Adults or various range for the American eel as 50 to developmental stages commonly occur 62' N. It occurs in warm brackish in freshwater, coastal waters, and and freshwater streams, estuaries, the open ocean from the southern tip and coastal rivers, and sometimes in of Greenland, Labrador, and cold freshwater trout streams in Newfoundland southward along the mountainous regions. Its distribu-Atlantic coast of North America, tion has increased because of its
j; MAINE MA 0
- E
'8 a
1.j ATLANTIC OCEAN 0
CAPE COD Coastal distribution V MILES 0 50 100 "oo "O KILOMETERS 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.
2
hardiness (as shown by the range of (Williams and Koehn 1984). Recent habitats it occupies, including pol- analysis of mitochrondrial DNA indi-luted areas), the ease with which cates that American and European eels it can be transplanted, and its belong to separate breeding popula-ability to travel across damp ground tions (Avise et al. 1986). The lack and wet vertical surfaces such as of interbreeding even though the dams. Adult eels are occasionally spawning areas overlap supports the found in landlocked lakes, primarily belief that American and European eels in the northeastern United.States. are different species. No available data conclusively point to geographic variations in morphology, and no MORPHOLOGY AND IDENTIFICATION AIDS subpopulations have been, distin-guished. Koehn and Williams (1978)
The American eel undergoes a noted protein differences among series of morphological changes in its juvenile eels collected from different life cycle, which are described in the locations along the Atlantic seaboard, later section on LIFE HISTORY. The but concluded that the differences following information was summarized were due to variation in selective primarily from Fahay (1978) and Tesch pressures among the environments in (1977). which the eels grew. Avise et al.
(1986) reported no significant The body is elongate (Figure 1). geographic differentiation in the The dorsal and anal fins are confluent mitochondrial DNA of 108 eels with the rudimentary caudal fin. collected from Maine to Louisiana.
Pectoral fins are present, but ventral This evidence strongly supports the (pelvic) fins are absent. Scales form conclusion that American eels are a at about 3 to 5 years of age, but are single, panmictic breeding population.
minute and embedded, causing eels to appear scaleless. The lateral line is well developed. The mouth is REASON FOR INCLUSION IN SERIES terminal; the jaws have bands of small, pectinate, or setiform teeth, The American eel supports and the vomer has a long tooth patch. commercial and limited recreational The number of vertebrae ranges from fisheries throughout most of its 103 to 111 but usually is 106 to 108 range. In the United States eels are (Schmidt 1913). . Ege (1939) presented marketed for human consumption and as comprehensive morphological data for bait for crabs and game fishes, A. rostrata. including striped bass (Morone saxatilis), cobia (Rachycentron No other anguillid eels occur in canadum), and largemouth bass North American coastal waters, but the (Micropterus salmoides). Adult eels American eel's spawning area often are shipped alive or frozen to apparently overlaps with that of the Europe where they frequently are European eel (Anguilla anguilla) smoked before. marketing. Elvers (McCleave et al. 1986). Mean myomere (immature eels typically < 60 mm counts for American and European eel long) have been harvested in Maine and larvae are 106.84 +/- 0.032 S.E. and shipped to Japan where they were 114.52 +/- 0.047 S.E. (Kleckner and cultured in ponds. Pond rearing of McCleave 1985). Externally visible eels is being developed in the United traits of adults are similar, but the States, and there is a potential for European eel has more vertebrae development and expansion of an eel (111-119; mean,115). Some authors culture industry.
have argued that European and American eels should be regarded as geograph- . The American eel is an important ical variants of the same species food of larger marine and freshwater 3
fishes. It preys on a variety of Middle and North Atlantic regions of other animals includina commercially the United States and the eastern important crabs and clams. Eels provinces of Canada.
contribute to the loss cf nutrients from freshwater rivers and lakes Different stages of the eel's because of their high organic intake, life cycle are known by a variety of large numbers, lengthy stay in fresh- common names that are used throughout water, and subsequent migration to sea the scientific literature. The larva (Smith and Saunders 1955). (leptocephalus) metamorphoses into an unpigmented glass eel which migrates into freshwater and gradually develops LIFE HISTORY pigmentation. The young eel is now called an elver. Elvers may remain in The life cycle of the American coastal rivers or may continue to move eel includes oceanic, estuarine, and upstream. The following growth phase, riverine phases (Figure 3). Many called the yellow eel, may last many details of its life history are only years. Yellow eels may be sexually generally understood or have been undifferentiated (gonads contain no inferred from knowledge of the definable gametes), hermaphroditic European eel. Much of what is known (oogonia and spermatogonia present),
has been derived from studies in the or sexually differentiated (females with oogonia; males with spermato-gonia). Because none of these stages are capable of reproduction, all yellow eels are immature. Maturation is accompanied by changes in body color and morphology; maturing eels that migrate downriver and through the ocean to the spawning grounds are known as bronze eels or silver eels.
Spawning The American eel is catadromous.
It spends most of its life in rivers, freshwater lakes, and estuaries, but returns to the sea to spawn (Figure 3). The age at maturity has not been well defined; Fahay (1978) reported that maturation occurred after age III for males and at ages IV-VII for females from northerly populations, although females more than 15 years old have been reported in large inland lakes (Hurley 1972; Facey and LaBar 1981). Eels mature at younger ages in the southeastern United States than in New England (Helfman et al. 1984a; Hansen and Eversole 1984; Facey and Helfman, in press).
Before seaward migration in the Figure 3. Diagrammatic representation fall, maturing eels begin metamor-of the life cycle of the American eel. phosis into the silver eel stage.
4
(This metamorphosis and the timing of 1.1 mm (Tesch 1977). Incubation, the reproductive migration are periods of American eel eggs are not described later.) known, but the eggs of artificially spawned Japanese eels (A. japonica) are known to hatch in 38-45 hours at Spawning by American eels has 23 'C (Yamamoto and Yamauchi 1974).
never been directly observed, and spawning areas have been inferred on the basis of collections of larvae. Relationships between eel size Spawning seemingly occurs in the and fecundity for 21 eels (418-845 mm Sargasso Sea as early as February and TL) were reported by Wenner and Musick may continue until at least April (1974) as log F = -4.29514 + 3.74418 (Kleckner et al. 1983; McCleave et al. log TL, log F = 3.2290 + 1.1157 log W, 1986). Tesch (1977), who summarized where F = number of eggs per female, TL = total length (mm), and W = total work by Schmidt (1923), Vladykov (1964), Smith (1968), and Vladykov and weight (g). Therefore, fecundity for March (1975), showed a spawning zone many American eels is between about 0.5 and 4.0 million eggs, with very south of Bermuda and north of the Bahamas that is centered at about 250 large individuals (1,000 mm) producing N. and 690 W. McCleave et al. (1986) perhaps as many as 8.5 million eggs.
The European eel has fecundity esti-reported that American eels spawn in the area from 19.50 to 29.00 N. and mates of 0.7 to 2.6 million eggs for 520 to 790 W., and that European eels individuals 630-920 mm TL (Boetius and Boetius 1980).
spawn from 230 to 30' N. and 480 to 740 W. The youngest stages of American eel larvae may coexist with Adult eels presumably die after European eel larvae, but American eel spawning. None have been observed larvae predominate west of 620 W. and to migrate up rivers, and spent eels south of 25' N. (Kleckner and McCleave have not been reported.
1985). The large overlap of spawning areas between American and European eels is evidenced by the capture Larval (Leptocephalus) Stage of leptocephali of both species in the Hatching probably begins and same trawl (McCleave et al. 1986).
Thermal fronts that separate the peaks in February, but may continue northern and southern water masses of through April (Kleckner et al. 1983; Kleckner and McCleave 1985; McCleave the Sargasso Sea are believed to form the northern limit of American eel et al. 1986). The larval stage lasts up to about I year. The body is spawning (Kleckner et al. 1983). The lanceolate, sharply pointed at both smallest American eel leptocephali that have been found (3.9-5.5 mm) were ends, and deepest at the middle; taken along the warm side of these illustrations were published by Tesch fronts. (1977) and Fahay (1978). The length at hatching has not been described for the American eel; however, the The depth at which spawning Japanese eel is about 2.7 mm long at occurs is not known, but morphological hatching and about 6.2 mm long 5 days and physiological evidence suggests after hatching (Yamamoto and Yamauchi that eels may migrate and spawn in the 1974). Kleckner et al. (1983) caught upper few hundred meters of the water larval American eels less than 5.5 mm column (Kleckner et al. 1983; McCleave long (perhaps less than 1 week old) and Kleckner 1985). The smallest from mid-February to early March.
leptocephali yet reported were taken Schmidt (1925) collected larvae 7 to in trawls fished at a maximum depth of 8 mm long in February. The smallest about 300 m (Kleckner et al. 1983). larvae collected by Vladykov and March Egg diameter of A. rostrata is about (1975) and Smith (1968) were 12 mm and 5
17 mm, respectively, and were caught Stream directly from the Sargasso Sea, in the summer. rather than by a more southerly route through the Bahama Islands (Kleckner American eel larvae grow as they and McCleave 1982). Eldred (1971) are transported by ocean currents. found larval A. rostrata in the Gulf Total lengths of larvae collected by of Mexico and Yucatan Straits, but Schmidt (1925) were 7 to 8 mm in mechanisms by which they are dispersed February, 20 to 25 mm in April, 30 to into the Gulf of Mexico and southward 35 mm in June, 40 mm in July, 50 to 55 to the coast of South America have not mm in September, and 60 to 65 mm by been determined.
the end of the first year of life.
The largest leptocephalus collected by Vladykov and March (1975) was 69 mm Glass Eel and Elver Stages long. A thorough analysis of available data from 4473 larval and During the pelagic phase, lepto-postmetamorphic American eels showed cephali reach the size and physiolog-that the relationship between length ical state. at which they begin to (Y: mm TL) and collection date (X: metamorphose. The early stages of Julian date) for 0-group leptocephali this transition involve a decrease in collected between 13 February and 15 length and weight due to a reduction October was Y=0.238 X - 6.569 (Kleck- in water content, changes in the ner and McCleave 1985). configuration of the head and jaws, and accelerated development of the Leptocephali grow rapidly until digestive system (Fahay 1978). After October when growth slows or stops, these changes occur, the eels are and many metamorphose into glass eels similar in overall morphology to yel-(Kleckner and McCleave 1985). Most low eels, but lack external pigmen-leptocephali undergo metamorphosis at tation and are therefore called "glass 55-65 mm TL and 8-12 months of age. eels." Glass eels actively migrate Limited evidence suggests that some toward land and freshwater, and eels may remain in the leptocephalus develop external pigmentation as they stage for more than 1 year. Smith enter coastal areas. These small, (1968) reported a leptocephalus 50 mm pigmented eels are called "elvers."
long near the spawning grounds during April; it was thus too long to have The young eels begin migrating been spawned in the immediate season upstream before pigmentation is (Fahay 1978). Vladykov and March complete. Initially they are active (1975) also suggested that larval A. at night and burrow or rest in deep rostrata may spend more than 1 year in water during the day (Deelder 1958).
the sea. They typically move up into the water column on flood tides and return to Larvae are transported from the the bottom during ebb tides (McCleave spawning grounds to the eastern sea- and Kleckner 1982; McCleave and board of North America by the Antilles Wippelhauser 1986). Similar behavior Current, the Florida Current, and the was reported for elvers at the mouth Gulf Stream. Power and McCleave of the Indian River, Delaware, by (1983) developed a model of surface Pacheco and Grant (1973), and for current drift to simulate the disper- elvers of the European eel by Tesch sal of eel leptocephali from the (1977). The cues that trigger the Sargasso Sea. Sampling has shown that change in behavior are not known, larvae are abundant in the Florida though Creutzberg (1959, 1961) showed Straits and in the area between that European glass eels were able to Bermuda and the Bahamas from April detect the odor of fresh water and through August (Smith 1968). Most alter their behavior accordingly.
leptocephali probably enter the Gulf Sorensen (1986) showed that American 6
eel elvers were strongly attracted to glass eels for the first few weeks and the odor of brook water and the odor almost entirely of pigmented elvers by of decaying leaf detritus and its the eighth week. In northern coastal associated microorganisms. Temper- Maine the entire run was composed of ature gradient may also aid in the glass eels. Smith and Saunders (1955) upstream orientation of glass eels reported the arrival of elvers in (Tongiorgi et al. 1986). Glass eels Passamaquoddy. Bay, New- Brunswick, in and elvers may delay upstream late April.
migration at the freshwater-saltwater interface while behaviorally and Small numbers of elvers reciularly physiologically adjusting to the new arrive in estuaries in the fall, and environment (Sorensen and Cianchini Fahay (1978) suggested that these 1986). "early" arrivals may be the earliest spawned individuals or a segment of Most glass eels and elvers move the main body of leptocephali that is into coastal areas, estuaries, and up moved northward more quickly than most freshwater rivers in late winter or by localized water currents. Alterna-early spring. Vladykov (1966) sug- tively, these elvers may be "late" gested that elvers generally arrive in arrivals produced from leptecephali southern estuaries earlier and at that did not metamorphose during the smaller sizes than in the north, but previous winter and spring.
records indicate considerable overlap in the timing of shoreward movements Elvers eventually begin swimming along the Atlantic coast. In the upstream and become most active during Southeastern and Middle Atlantic the day (Sorensen and Bianchini 1986).
States, migrating glass eels and The onset of this active upstream elvers have been collected from Janu- migration may be triggered by changes ary through May (Jeffries 1960; Smith in water chemistry caused by intrusion 1968; Fahay 1978; Hornberger 1978, of estuarine water during high spring cited by Sykes 1981; Sykes 1981; tides (Sorensen and Bianchini 1986).
Helfman et al. 1984a). Tesch (1977) indicated that elvers of A. anguilla orient to river currents Glass eels and elvers may reach for upstream movement; if the current New England estuaries -as early as late becomes too weak or too strong (veloc-winter (Jeffries 1960), but the main ities not specified), the fish may upstream migration is in spring. move into backwater areas, severely Glass eels have arrived at the coast delaying upstream progress. Basic of Maine from the end of March to similarities in behavior of European about the third week of May (Dr. J. D. and American eel elvers suggest that McCleave, University of Maine at those of American eels would be Orono; pers. comm.). In Rhode Island similarly affected by fast or slow the elver migration peaks during April river currents.
and May (Haro 1986; Sorensen and Bianchini 1986), whereas in Maine the Haro (1986) indicated that the run is primarily from late April to main concentration of elvers in a June (Ricker and Squiers 1974; Sheldon coastal Rhode Island stream required 1974). Most upstream migrating eels about 1 month to move a distance of arriving in May at the freshwater 200 m above the tidal zone, and that interface in a Rhode Island brook were some American eels may continue mi-not completely pigmented, but most grating upstream as yellow eels of were fully pigmented by July (Sorensen age II or older. The scarcity of and Bianchini 1986). In 1974 the run small, young eels in lakes that are along the southern and central far inland supports the idea of con-portions of the Maine coast was tinued upstream migration by yellow composed primarily of unpigmented eels (Hurley 1972; Facey and LaBar 7
1981; Kolenosky and Hendry 1982). In addition to the possible Eels ascending the eel ladder at the freshwater-saltwater variation in the Moses-Saunders Dam on the St. Lawrence sex ratio, there seems to be geog-River at Cornwall, Ontario (approxi- raphic variation in the distribution mately 1600 km, from. the ocean), were of the sexes. Vladykov (1966) wrote generally 3 to 8 years old (Liew that males predominate from New Jersey 1982). to Florida, whereas females predomin-nate from New York to Newfoundland.
Although work in South Carolina and Yellow and Silver Eels Georgia did not support the idea that southern stocks are predominantly Many investigators (e.g., Bigelow male, the percentage of males was and Schroeder 1953; Vladykov 1966) higher than that reported in northern have stated that female yellow eels areas. Vladykov believed that a occur primarily in freshwater, and latitudinal change in sex composition males generally in saltwater or was related to the size differences in brackish water. Dolan and Power elvers along the coast, and supposed (1977), however, after an extensive that the smaller elvers entering review of literature, concluded that southern streams become males and the this "female-freshwater, male-salt- larger elvers entering northern water" theory was not supported. In a systems develop into females. The Georgia river, the percentage of presumed geographic distribution of sexually differentiated yellow eels sex in the American eel may be a that were males was 36 in the estuary result of selectivity of sampling gear and 6 in freshwater (Helfman et al. and the possible exclusion of smaller 1984a). In the Cooper River system in males in northern studies, plus the South Carolina the percentages of assumption that the geographic dis-males were 7 in saltwater (Michener tribution of sex in the American eel 1980), 5 in brackish water (Hansen and would parallel that demonstrated for Eversole 1984), and 3 in freshwater the European eel (Dolan and Power (Harrell and Loyacano 1980). Winn et 1977).
al. (1975) reported higher percentages of males in freshwater and females in Limited evidence suggests that saltwater in Rhode Island streams and the gender of American eels is deter-estuaries, but did not explain the mined to some extent by environmental methods used to determine sex. Dolan factors. Fahay (1978) wrote that the and Power (1977) indicated that sex of the European eel can be histological examination of the gonads environmentally influenced, but indi-is necessary to determine sex in eels. cated that the factors responsible could only be speculated about. The long developmental period in fresh-Sexual differentiation does not water or brackish water in combination occur until eels are about 200-250 mm with juvenile hermaphroditism provides long (Dolan and Power 1977). Before a setting in which environmental completion of the differentiation factors could regulate the gender of process some eels have gonads con- eels.
taining male and female gametes (juvenile hemaphroditism; Tesch 1977), Male American eels tend to be but after gender is established, it more abundant in estuaries than in does not change (Fahay 1978). Dif- upriver sites, and more males have ferentiated and undifferentiated been found in Southeastern States than yellow eels may overlap considerably in northern locations. One possible in size and age (Gray and Andrews explanation is that male leptocephali 1970; Dolan and Power 1977; Hansen and and elvers do not migrate as far as Eversole 1984; Helfman et al. 1984a). females, and hence remain in southerly 8
or downstream areas. It is also pos- (see Stearns and Crandall 1984).
sible that male eels prefer hioher Large size would not be beneficial to salinities than females and move male eels because small mature males downstream to coastal areas after they can produce an abundance of gametes.
are differentiated, but this behav-, However, the fecundity of female. eels ioral pattern has not been observed is highly dependent on size. There-and it would not explain the lati- fore,. females that grow slower but tudinal trend. Even where males have reach larger sizes, such as those in been found to be most abundant, in northern and upriver locations, Georgia estuaries (Helfman et al. probably contribute more eggs to the 1984a), they are still outnumbered by next generation than do females that females. grow rapidly but mature at younger ages and smaller sizes, such as those The fact that American eels in the southeastern United States.
appear to be a single, panmictic Natural selection would perpetuate population suggests that latitudinal such a system where the fastest variations in the sex ratio are not growing eels tend to be males whereas genetically determined but could be eels that grow slower but get larger due to variations of environmental are females (Helfman et al., in factors, such as food quality and press).
population density (Fahay 1978).
Parsons et al. (1977) believed that Eels are more active at night stocking of European eel elvers into than during the day. Direct observa-Lough Neagh, Northern Ireland, led to tion of yellow eels in a north Florida a higher population density and a cave-spring indicated . that eels marked increase in the proportion of changed. behavior at dawn and dusk, male eels that subsequently emigrated. when light levels were generally from the. lake. Similarly, Egusa 10-100 lux (Helfman 1986). Laboratory (1979) indicated that elvers of A. studies have shown that silver eels anguilla and A. japonica grown in are also more active in darkness than Japanese ponds under crowded condi- in light, and that activity peaks tions produced higher percentages of during light-dark transition (Edel males than are found in wild popu- 1975, 1979). Telemetry showed that lations, suggesting that variations in yellow eels in a tidal creek were the sex ratio of anguillid eel popu- generally inactive during the day and lations may be related to population active at night (Helfman et al. 1983).
density. Salinity apparently is not Activity was, however, influenced by an important sex determinant; sex tidal cycles with eels exhibiting ratios were similar in the freshwater greater activity during high tide. In and brackish water culture ponds a tidal cove studied in Maine, eels studied by Egusa. were moderately abundant in seine hauls at night but were never captured Growth rate, which is affected by during the day (McCleave and Fried temperature, food availability, and 1975). Commercial harvest information length of the growing season, might also indicates that eels are more also be a factor in determining sex. active at night (see Eales 1968; Tesch This could result in different life 1977).
history strategies for males and females (Helfman et al., in press). Estimates of the home range of Eels that grow rapidly, such as those eels extend to 3.4 ha in small in highly productive southern streams, tidal rivers, and tidal estuaries, may have greater repro- creeks (Gunning and Shoop 1962; ductive fitness if they are males. Bianchini et al. 1982; Bozeman et al.
This is especially true if rapid 1985); from 2.4 to 65.4 ha in a large growth results in earlier maturation lake (LaBar and Facey 1983); and < 100 9
m along a tidal creek in summer in a phosed) eels appear to be better Massachusetts salt marsh (Ford and adapted to swimming than yellow eels Mercer 1986). Ford and Mercer (Holmberg and Saunders 1979).
suggested that large eels may establish territories in the wider Few details are known about the marsh creeks, thus restricting small oceanic spawning migration of the eels to narrower creeks at the back American eel. The first collections of the marsh. Agonistic interactions of adults in offshore waters were in which large eels displace smaller reported by Wenner (1973) in the open eels have been reported elsewhere ocean southeast of Cape Cod; east of (Helfman 1986). Assateague Island, North Carolina; and southeast of Chesapeake Bay. The Eels begin the spawning migration means by which eels locate the spawn-in late summer' and fall throughout ing grounds are poorly understood.
much of New England and eastern Miles (1968) concluded that eels were Canada. Migration from lakes that are capable of noncelestial orientation well inland may begin earlier. (southward), and Rommel and Stasko Catches of eels leaving Lake Champlain (1973) indicated that eels may use by way . of the Richileau River were geoelectric fields generated by ocean heaviest from June to August (R. currents for orientation. Robins et Thuot, commerical fisherman, Iber- al. (1979) photographed two adult ville, Quebec; pers. comm.). Eels Anguilla eels on the floor of the seem *to leave later in the South- Atlantic Ocean in the Bahamas at eastern and Middle Atlantic United depths of about 2000 m, and although States than in New England States. it was impossible to identify the This delay may function to synchronize species, the authors believed the arrival at the spawning grounds in the specimens to be prespawninq A.
Sargasso Sea (Wenner 1973; Facey and rostrata.
Helfman, in press). Many downstream migrating eels may not yet have Stasko and Rommel (1977), who developed the external characteristics tracked five migrating eels in the associated with the migratory silver lower St. Croix River estuary, New eel stage. Northern eels may begin Brunswick, Canada, reported that one migration at an earlier developmental eel moved 25 km in 20 h and another stage, perhaps to compensate for the moved 38 km in 40 h. The eels they longer time required to reach the studied showed considerable vertical spawning grounds (Wenner 1973). movements in the water column; behavior did not change with diel or The metamorphosis from yellow eel tidal cycles. Edel (1976) believed to silver eel includes several physio- that the depth at which American eels logical changes: (1) color change (to migrate in the ocean varied with light a metallic, bronze-black sheen; pec- intensity, and that swimming depth toral fins change from yellow-green to varied with turbidity of the water.
black); (2) fattening of the body; (3) thickening of the skin; (4) enlarge-ment of the eyes and changes in visual GROWTH CHARACTERISTICS pigments in the eye in preparation for migrating at greater ocean depths (Vladykov 1973; Beatty 1975); (5) For the American eel the length increased length of capillaries in the at hatching is not known; however, the rete of the swim bladder, which also Japanese eel hatches at about 2.7 mm may be an indication of migration at (Yamamoto and Yamauchi 1974). Growth greater depths (Kleckner and Kruger rate of American eel leptocephali has 1981); and (6) degeneration of the been estimated to be 0.243 mm/day digestive tract. Silver (metamor- (Wippelhauser et al. 1985). Larvae 10
typically reach 40 to 70 mm after I age and poor predictability of age year. The metamorphosis from plank- from size. Lengths of eels at various tonic larva to the upstream migrating ages in northern locales are summa-form is accompanied by a decrease in rized in Table 1. Eels in the South-length and weight due to reduction in eastern United States seem to mature water content of the body. Glass eels at younger ages and smaller sizes and captured while migrating upstream in therefore may not get as large as late February in Georgia were 49-56 mm northern eels (Helfman et al. 1984a).
long and 250-300 days old (Helfman et al. 1984a). The length of glass eels The great variability in length collected from January through April within an age class makes it virtually in South Carolina averaged 55 mm long impossible to accurately estimate eel and ranged from 45 to 65 mm (Horn- growth rates from length-age regres-berger et al. 1978). Ricker and sions. Perhaps the best way to deter-Squiers (1974) reported that glass mine growth rates is to monitor eels and elvers caught along the coast individuals during long-term tagging of Maine from late April through the studies. Helfman et al. (1984b) com-end of June averaged 59.2 mm (95% pared growth rates estimated from confidence interval, 57.5-60.8 mm). length-age analysis to measured growth Elvers grow slowly, reaching about 127 rates of tagged eels (initial size:
mm after the first year in freshwater 275-475 mm) in a Georgia estuary. On (Bigelow and Schroeder 1953). Yellow the basis of indirect measurements eels typically grow slowly but reach (length-age regression and mean-weights up to 6.8 kg; females caught length-at-age analysis), estimated from the St. Lawrence River were 960 annual growth rates were 44 mm/year, to 1,270 mm in length and weighed 0.9 whereas independent direct measure-to 4.5 kg (Fahay 1978). Females grow ments (seasonal summation and long-to a larger size than males. term recaptures) yielded values of 57 and 62 mm/year. Gunning and Shoop Eels have been aged from otoliths (1962) reported that four recaptured and scales.* Otoliths in eels consist eels (initial lengths, 255-915 mm) in of a translucent nucleus (formed at Louisiana streams grew an average of sea), surrounded by broad opaque 140 mm/year (range,46-325 mm/year).
summer zones and narrow translucent In Massachusetts salt marshes, winter zones (Gray and Andrews 1971). Haedrich and Polloni (1978) showed Eels in Canadian waters formed their that eels averaging 52 cm long grew first scales at 160 to 200 mm during about 4% per year, and Polloni et al.
their third to fifth year of life, and (1980) reported that eels 500-700 mm annual rings were formed on the scales long grew about 6% (range, 4.1-8.4%).
in subsequent winters (Smith and The lengths of 10 eels, tagged in 1979 Saunders 1955). Thus, in northerly and recaptured in 1986 in Vermont areas, age in years generally is the waters of Lake Champlain increased an number of scale rings plus three. average of 9.7 cm over the 7-year However, because scales continue to period (Dr. G. W. LaBar, University of form as the eel grows, different Vermont, Burlington; pers. comm.).
scales from the same fish yield different ages (Smith and Saunders 1955). Although otoliths may show COMMERCIAL AND SPORT FISHERIES more than one opaque ring in a year (Deelder 1976), they are preferred for estimating the age of eels. The European market has been the major outlet for U.S. landings of Growth rates within year classes yellow and silver eels (Fahay 1978).
are highly variable, leading to Eels are hardy and can be densely considerable variation in length at packed and shipped alive if they are 11
Table 1. Total lengths (cm) of American eels at various ages in different localities.
Locality New-Age foun*- New b c d Rhode New f Delawage South group land Brunswick Ontario Vermont Island Jersey River* Carolina 12-16 IV III 16-19 19-20 14-25 26-33 21-23 20-32 20-23 18-28 29-45 IV 23-30 22-40 22-32 27-46 29-32 24-32 30-59 V 25-40 26-50 29 28-51 26-34 33-62 VI 29-46 22-56 22-67 28-51 41-67 28-42 32-63 VII VIII 36-50 30-62 29-67 29-58 36-67 29-43 42-66 43-59 32-62 39-70 43 33-64 44-70 35-47 48-69 iX 49-66 38-66 33-74 57 38-62 37-74 35-50 46-55 60-78 48-66 44-86 45-71 37-65 44-86 40-52 52-66 45-54 XI 66-84 63-90 50-79 46-65 63-90 XII 75-77 67-94 48-80 67-94 43-64 XIII XIll 68-98 45-72 68-98 55 XlV 78-97 43-80 78-97 56-59 78-104 53-78 78-104 XVI XVI 78-100 53-85 77-100 XVII 96-99 49-83 95-99 91 58-90 51-82 66-86 52-85 XXII 58-85 80 aGray and Andrews 1971.
Smith and Saunders 1955. Ages estimated by adding 3 ye ars to the number of cscale rings counted by authors.
dHfurley 1972.
Facey 1980.
fBieder 1971.
"Ogden 1970.
gJohnson 1974.
hHansen and Eversole1984. Ages estimated by adding 1 year to the number of inland years reported by authors.
12
kept moist, cool , and supplied, with Table 2. Preliminary commercial oxygen. .Although live eels are fishery landings of eels in Maine and preferred in Europe, many are shipped Massachusetts, 1980-198 5a. (Informa-frozen. tion provided by R. Schultz, Resource Statistics Division, National Marine Commercial fishermen use a vari- Fisheries Service).
ety of methods to catch eels, includ-ing lift nets,' drift nets, traps, weirs, otter trawls, pound nets, fyke Maine Massachusetts nets, spears, handlines, eel pot's,and Year weight value weight -value haul seines (Fahay 1978). Yellow eels (kg) (kg) in freshwater or brackish water are taken primarily with baited traps or 1980 47,938 $111,061 841. $219 eel pots.
1981 25,057 45,308 - -
A summary of catch statistics 1982 20,478 36,637. 205 23 along the Atlantic coast from 1955 to 1973 showed that landings from the 1983 5,409 8,925 80 26 Middle Atlantic (New Jersey to Virginia) consistently exceeded those 1984 -- 2,148 1,679 from the North Atlantic (Maine to New York) and South Atlantic (North Caro- 1985 10,955 18,288 - -
lina to Florida) (Fahay 1978). From 1970 to .1973, the annual North Atlantic harvest averaged 125,418 kg, aDoes not include 9 kg reported in New with an average value of $84,000. In Hampshire *in1981.
1977 the eel landings for Maine, New Hampshire, and Massachusetts were about 79,700, 2,700, and 143,300 kg, "During the years from roughly valued at $263,000, $5,000, and 1975 to 1980 the estuarine eel fishery
$173,000, respectively (U.S. Depart- grew considerably in Massachusetts, ment'of Commerce 1984). Massachusetts principally . on Cape Cod, south of landings were about 100,300 kg in Boston and in southeastern 'Massachu-1978 and 81,800 kg in 1979 (U.S. setts coastal towns. Numbers of men Department of Commerce 1980a), and fishing increased as well as the total Maine landings were about 60,500 kg landings, although accurate statistics in 1978 and 50,400 kg in 1979 (U.S. are lacking. This was due to the high Department of Commerce 1980b). By ex-vessel prices paid to fishermen, 1985 the Massachusetts catch was less the result of renewed interest and an than 3,800 kg (E.D. Hubbard, Massachu- ever-increasing European eel demand.
setts Division of Marine Fisheries; Whereas nearly every European country pers. comm.) . Landings in Maine and consumes eels, apparently loca~l Massachusetts in 1980-85 are shown in supplies could not meet the total Table 2. Some of the landing statis- demand and so North American exports tics may be inaccurate. began to fill this gap.
.Although U.S. eel harvests seemed "Somewhat abruptly in 1981 most to be increasing through the 1970's, of these U.S. export markets plum-eel fishing in New England has meted. due to a number of factors, but declined drastically in recent years. principally due to the very tight The situation may be due to reasons economic situation in the U.S. as well cited by E. D. Hubbard, in her as abroad. Other contributing factors assessment of the Massachusetts eel were contaminated shipments of eels fishery (pers. comm., June 1986). from Canada and grading (live eels) 13
problems. Exports of all finfish have 1965-68, $300/kg in 1969, and $330 to slumped over the last several years $925/kg in 1971-73 (Fahay 1978; Egusa due to an inflationary U.S. dollar. 1979). Prices paid for European eel During this time, the Europeans elvers in Japan initially were imported eels from new sources across equivalent to those paid for local the Pacific. elvers, but European eels were inferior in the pond culture systems "Several well established eel because of poor growth and disease buyers along the American East Coast problems; in 1973, the Japanese paid closed their doors during 1982, [pri- only $30 to $50/kg for European elvers marily due] to high shipping costs and (Egusa 1979).
inflated exchange rates. Because buy-ers were not interested in eels, or at Reports of $100 to $2,000 per kg much lower prices, very few persons attracted some Maine fishermen into fished during 1982, continuing through the elver market, but they found that to the present. The last major buyer/ these reports were inflated over the exporter in Massachusetts ceased his actual value of a successful shipment eel operations in 1985. With unfavor- (Ricker and Squiers 1974). Elvers able market conditions continuing in vary widely in size, and the number Europe over the last 4 to 5 years, the per kilogram may range from about coastal eel fishery here in Massachu- 2,200 to more than 12,000 (Ricker and setts has been practically nonexist- Squiers 1974). Sheldon (1974) ent. In the fall months, the tradi- reported locations and techniques for tional Christmas eel demand in the catching, holding, and transporting larger U.S. cities means a short- elvers in Maine. In Maine, elver term, high priced market for fisher- landings were 10 metric tons in 1977 men. But other than scattered and and 7.6 in 1978, valued at $110,000 seasonally limited sales demand, and $63,251 (Dow 1982). Massachusetts fishermen have not set their pots, prohibits harvesting of elvers except although the interest is very high. for aquaculture purposes, for which a One buyer in Maine is doing business permit is required. From 1978 to 1986 with some of the local fishermen and only one such permit was requested and another company in New Hampshire has issued (E.D. Hubbard; pers. comm.).
very recently expressed interest in The Japanese Elver Culture Association exporting eels." began assessing the performance of Maine elvers in the mid 1970's. There It is possible, however, that have been reports that the elvers of European demand for American eels may the American eel did not thrive and increase in the late 1980's because of that the Japanese eel culture industry the accidental release of toxic began buying A. japonica elvers from chemicals into the upper Rhine River China (L. Flagg, Maine Depa.rtment of in fall 1986; hundreds of thousands of Marine Resources; pers. comm.).
European eels were killed. If the accident significantly affects The feasibility of commercial European eel fisheries for many years, "grow-out" operations in North an increased demand for American eels Carolina was assessed by Easley and might extend into the 1990's. Freund (1977). Interest in culturing was stimulated by rising prices during A fishery for European eel elvers the late 1960's and early 1970's, but began in Europe during the late 1960's considerable refinement of techniques to supply Japan's demand for young was needed. Development of eel aqua-eels to use in pond culture. Elvers culture has focused on methods for were packed live in boxes and shipped collecting elvers and on physical to Japan, where prices paid for local features of grow-out systems. Hormone A. japonica elvers were $7/kg in injections, can be used to induce 14
maturation of female American eels (1982, cited by Bozeman et al. 1985)
(Edel 1976), but proper spawning estimated eel biomass at 75 kg/ha in conditions are unknown, and eel cul- the tidal section of a Rhode Island ture remains dependent on capturing river. Bozeman et al. (1985) reported wild elvers. Hinton and Eversole about 13 kg/ha in a Georgia tidal (1978, 1979, 1980) evaluated the toxic creek. A 600-m section of a marsh effects of chemicals commonly used in creek in Massachusetts was estimated aquaculture on glass eels (mean to contain about 350 yellow eels, a length, 55 mm), elvers (mean length, stock density equivalent to 875 eels/
97 mm), and yellow eels collected from ha (Ford and Mercer 1986). Standing South Carolina rivers. Lower tem- crops up to about 80 kg/ha were peratures and the shorter growing reported in lakes in New Brunswick, season might make commercial culturing Nova Scotia, and Prince Edward Island of eels less practical at northern (Smith and Saunders 1955). The eel latitudes. biomass in Coleback Lake, Maine, was about 50 kg/ha (Rupp and DeRoche Restrictions on eel harvest vary 1965), whereas estimates in shallow among the North Atlantic states. In (<2 m) portions of Lake Champlain, Maine the size of catch is not Vermont, were 161 to 421 kg/ha (LaBar regulated, but certain permits and and Facey 1983). The biomass esti-regulations pertain to some towns and mates in Lake Champlain may have been rivers (Ricker 1976). Commercial high because there had been no com-fishing licenses are issued by the mercial eel fishery on the lake before Department of Marine Resources, or by the study.
the Department of Inland Fisheries and Wildlife (for inland waters). The Estimates of mortality or other Department of Marine Resources also vital statistics of eel stocks gen-issues licenses for anyone buying or erally have not been reported, and selling eels in the wholesale trade. factors regulating survival or stock In Massachusetts, coastal towns size have not been evaluated. Helfman regulate commercial eel fishing in (unpubl. MS.') suggested that the saltwater and estuaries (Amaral 1982; eel's long life in freshwater may make E.D. Hubbard; pers. comm.). Only eels the stocks prone to local overharvest.
102 mm (4 inches) long or longer may *Keefe (1982) suggested that declines be harvested, and only by nets, pots, in catch of eels per unit of fishing spears and angling. Commercial effort in North Carolina indicated fishing for eels is permitted in overharvest. Because all American inland waters, but a permit and eels spawn in the Sargasso Sea, and fishing license are required. Only there are apparently no genetically eel pots with a mesh no less than 13 distinct stocks or subpopulations mm (0.5 inch) and a funnel opening not (Koehn and Williams 1978; Avise et al.
greater than 51 mm (2 inches) may be 1986), overharvest in one region could used. Fishermen are required to keep affect recruitment in other regions.
daily logs, and no eels less than 102. Kolenosky and Hendry (1982) suggested mm long may be taken. The Division of taking a conservative approach to the Marine Fisheries issues the. licenses harvesting of eels in Canadian waters required to sell eels. New Hampshire also prohibits the taking of eels less than 102 mm long (T. Spurr, New Hamp-shire Fish and Game Department, IDevelopment and expansion of the Concord; pers. comm.). fishery for American eels in Georgia.
G.S. Helfman, Department of Zoology, Population size and biomass University of Georgia, Athens, GA estimates of American eels are scarce 30602. Project summary, University and vary widely. Bianchini. et al. of Georgia Sea Grant Program, 1983.
15
of Lake Ontario, partly because of the eaten from spring through fall.
declining catch per unit of effort. Crustaceans, bivalves, and polychaetes Nevertheless, some management policies were the major prey of eels in lower allow or encourage locally heavy Chesapeake Bay; blue crabs exploitation of migrating silver eels (Callinectes sapidus) and soft-shell or elvers under the assumption that clams (Mya arenaria) were significant the numbers of elvers returning in prey (Wenner and Musick 1975). Eels later years will be maintained by shorter than 40 cm in New Jersey escapement of spawning stock from streams ate mainly aquatic insects other areas. whereas larger eels fed mostly on fishes and crustaceans (Ogden 1970).
American eels are caught by sport Most fishes eaten were bottom dwel-fishermen along the entire east coast lers, reflecting the tendency of eels of the United States. The estimated to feed near the bottom. In Vermont catch in 1979 by marine and estuarine waters of Lake Champlain, eels ate recreational fishermen was 113,000 primarily insects, crayfish, and eels in the North Atlantic States, fishes; larger eels (> 58 cm) ate more 172,000 in the Mid Atlantic, 47,000 in crayfish and fishes than did smaller the South Atlantic, and 43,000 in the eels (Facey and LaBar 1981). Eels Gulf coast region (U.S. Department of have been considered sionificant Commerce 1981). predators on young salhionids, but this is not well supported by. the litera-ture. In New Brunswick streams, only ECOLOGICAL ROLE 6 of 300 eels with food in their stomachs had eaten salmonids (Godfrey 1957). - Of 4,340 European eels Yellow eels are nocturnal, and a examined from six Welsh rivers, Sinha significant amount of their feeding is and Jones (1967) found only 10 that at night (Helfman 1986). . They prob- had eaten salmonids.
ably depend more on scent than on sight to locate food (Fahay 1978). Little has been published about The diet is diverse and generally predation on eels. Ho~rnberger et al.
includes nearly all types of aquatic (1978) reported that elvers and small fauna that occupy the same habitats. yellow eels were eaten by largemouth Eels swallow some types of prey whole, bass and striped bass in the Cooper but also can tear pieces from large River, South Carolina, but that eels dead fish, crabs, or other items. were never a major component of these Helfman and Clark (1986) documented predators' diets. Leptocephali, glass the ability of eels to grasp large eels, elvers, and small yellow eels food items and spin rapidly to tear probably are eaten by a variety of away pieces. Eels in freshwater feed predatory fishes. Sorensen and on insects, worms, crayfish and other Bianchini (1986) stated that older crustaceans, frogs, and fishes. eels eat incoming glass eels and Elvers collected from the Cooper elvers. Grown eel.s are eaten by River, South Carolina, ate aquatic species of eels other than insects (mainlv larval and adult anguillids and by gulls, bald eagles chironomids), cladocerans, amphipods, (Haliaeetus leucocephalus), and other and fish parts (McCord 1977). The fish-eating birds (Sinha and Jones diet of yellow eels from the Cooper 1967; Seymour 1974).
River varied with eel size and season.
More types of food were eaten by Crane and Eversole (1980) found intermediate-sized eels than by elvers no parasites on glass eels migrating or maturing eels; fish occurred in the into the Cooper River, South Carolina, diet primarily in winter and spring, but examinations of elvers yielded whereas insects and mollusks were four genera of protozoans (Trichedina, 16
Ichthyophthirius, Myxidium, and and Stauffer (1980), and claimed that Myxobolus) and one species of acclimation temperature does influence monogenetic trematode (Gyrodactylus preferred temperature. They found a anguillae). Crane and Eversole (1981) final temperature preferendum of 17.4 reported that 214 of 218 yellow eels +/- 2.0 'C (95% confidence interval).
collected from brackish waters of the Marcy (1973) reported that American Cooper River, South Carolina, were eels survived passage through the parasitized by I or more of 22 cooling system of a nuclear power helminth species. About 48% of yellow plant, during which they were exposed eels collected from brackish portions to elevated temperatures for 1-1.5 hr.
of the Cooper River were infested with Poluhowich (1972) suggested that the one or more ectoparasitic species from American eel's multiple types of hemo-the classes Monogenea and Crustacea globins serve to maintain a nearly (Crane and Eversole, in press). constant blood oxygen affinity when Levels of parasitism by Ergasilus the eel is exposed to temperature cerastes and E. celestis varied changes. American eels acclimated at seasonally and with size and age of 10 to 20 'C fed regularly and the host. Parasites of American eels exhibited compensatory adjustments in in Quebec included protozoans, oxygen consumption characteristic of trematodes, nematodes, cestodes, and many ectotherms (Walsh et al. 1983).
copepods (Hanek and Molnar 1974). The However, acclimation to temperatures myxosporidian protozoan Myxidium
- 5 'C for over 5 weeks resulted in zelandicum has been found in the kid- cessation of feeding and a dramatic neys and on the gills of the Americarf decrease in oxygen consumption.
eel (Komourdjian et al. 1977).
Salinity ENVIRONMENTAL REQUIREMENTS The mechanisms by which glass eels or elvers orient during their shoreward migration have not been Temperature described. Eels are known for their extremely sensitive sense of smell, The eel's broad geographic range and olfaction may play a role in the and diverse habitats suggest flexible ability of elvers to locate freshwater temperature requirements. Elvers and (Sheldon 1974; Sorensen and Bianchini yellow eels live in waters ranging 1986; Sorensen, 1986). European glass from cold, high-elevation or high- eels and elvers become positively latitude freshwater streams and lakes rhectactic when they first encounter to warm, brackish coastal bays and freshwater that is mixed with seawater estuaries in the Gulf of Mexico. (Tesch 1977). Alterations of patterns Jeffries (1960) found elvers at tem- or magnitudes of freshwater inflows to peratures as low as -0.8 'C. bays or estuaries could alter flow regimes and thereby affect the size, Barila and Stauffer (1980) timing, and spatial patterns of acclimated yellow eels to a range of upstream migrations by elvers.
temperatures between 6 and 30 'C and then measured preferred temperatures. Like temperature requirements, Although preferred temperatures tended salinity requirements of postlarval to increase with increased acclimation eels can be inferred as being broad temperature, group differences were from the fact that the postlarval eels not significant, and the authors occur throughout a gradient of strict-reported a final mean temperature ly fresh to brackish waters. Elvers preference of 16.7 'C. Karlsson et do appear to delay upstream migration al. (1984) disagreed with the tech- at the freshwater interface, however, niques and interpretation of Barila perhaps to permit physiological 17
adaptation to the new environment in northern habitats lie dormant in (Sorensen and Bianchini 1986). Lepto- the bottom mud during winter.
cephali are in near-ionic equilibrium with sea water (Hulet et al. 1972),
but the osmolality of glass eels and River and Tidal Currents elvers has not been reported.
The glass eel's and elver's nocturnal activity and reliance on Dissolved Oxygen tides for upstream movement have already been mentioned. Flow Dissolved oxygen requirements alteration in estuaries might affect have not been thoroughly documented, upstream migration of small, eels.
but eels generally select water with Dams and other obstructions pro-high oxygen tension (Hill 1969). bably inhibit migrating elvers (Tesch Elvers are sensitive to low oxygen, 1977), and limit recruitment to and should be held and transported in upstream sites; however, eels can water with an oxygen concentration of travel over wet vertical surfaces such at least 11 ppm (Sheldon 1974). as dams.
Because elvers can absorb oxygen through the skin, they can better be Tides and the time of day transported damp and in air than in affected movements of yellow eels in poorly oxygenated water. Evidently a tidal creek in Georgia (Helfman et this is also true of adult eels. al. 1983). Movements of eight Tesch (1977) wrote that, "The capacity telemetered eels were restricted to of the adult eel to survive in both the main creek channel during the day, air and water is associated with its but at night the fish were near the ability to use both branchial and mouths of feeder creeks at low tide or cutaneous modes of respiratory gas in flooded marsh areas during high exchange. The eel survives better in tide. Helfman et al. (1983) termed air than in poorly oxygenated or this movement "a nocturnal activity polluted water...." pattern modified by tidal flow," and suggested that such movements were foraging trips.
Habitat Structure Contaminants Postlarval eels tend to be bottom dwellers and hide in burrows, tubes, Little work has been done on snags, plant masses, other types of toxic effects of pollutants or the shelter, or the substrate itself tolerance limits in American eels.
(Fahay 1978). This behavior is Tolerance would be expected to vary reflected in their food habits, with developmental phase, and the protects them from predators, and eel's long residence in freshwater influences commercial fishing rivers could lead to repeated doses of techniques. Few other freshwater toxicants and accumulation of toxic fishes display similar habitat use; levels (Holmberg and Saunders 1979).
interspecific competition fcr living Work done by Hinton and Eversole space may therefore be limited. The (1978, 1979, 1980) on toxicity of presence of soft, undisturbed bottom aquacultural chemicals to various life sediments is important to migrating stages of eels suggested that elvers as shelter. Edel (1979) tolerance to chemicals increases with indicated that eels in his exper- size or age.
imental systems were less active when shelter was present than when it was In September 1976 the New York lacking. Vladykov (1955, cited by State Department of Environmental Fahay 1978) reported that adult eels Conservation and the Department of 18
Health banned the possession and sale eels (Blake 1982). This ended the of eels taken from the Hudson River Hudson River fishery for eels. In and Lake Ontario because levels of 1978 the restrictions were modified to polychlorobiphenyls (PCBs) exceeded allow sales of Lake Ontario eels to the U.S. legal maximum le'vel of 2 ppm: foreign markets, which apparently 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.
19
LITERATURE CITED Amaral , E. H. 1982. Massachusetts rostrata (LeSueur), in Rhode Islard.
eel fishery summary report. Page 42 M.S. Thesis. University of Rhode in K.H. Loftus, ed. Proceedings of Island, Kingston, R.I. 39 pp.
t--he ;1980 North American eel confer-ence. Ontario Fish. Tech.,.Rep. Ser. Bigelow, H. B., and W. C. Schroeder.
No. 4. Ontario Ministry, of Nat. 1953. Fishes of the Gulf of Maine.
Resour. Toronto. U.S. Fish Wildl. Serv. Fish. Bull.
- 53. 577 pp.
Avise, J. C., G. S. Helfman, N. C.
Saunders, and L. S. Hales. 1986. Blake, L. M. 1982. Commercial fish-Mitochrondrial DNA differentiation ing for eels in New York State.
in North Atlantic eels: population Pages 39-41 in K. H. Loftus, ed.
genetic consequences of an unusual Proceedings of the 1980 North life history pattern. Proc. Natl. American eel conference. Ontario Acad. Sci. USA 83:4350-4354. Fish. Tech. Rep. Ser. No. 4.
Ontario Ministry of Nat. Resour.
Barila, F. Y., and J. R. Stauffer, Jr. Toronto.
1980. Temperature behavioral responses of the American eel, Boetius, I., and J. Boetius. 1980.
Anguilla rostrata (LeSueur), from Experimental maturation of female Maryland. Hydrobiolooia 74:49-51. silver eels, Anouilla anguilla.
Estimates of fecundity and energy Beatty, D. D. 1975. Visual pigments reserves for migration and spawning.
of the American eel, Anguilla Dana 1:1-28.
rostrata. Vision Res. 15:771-776.
Bozeman, E. L., G. S. Helfman, and T.
Bertin, L. 1956. Eels: a biological Richardson. 1985. Population size study. Cleaver-Hume Press Ltd., and home range of American eels in a London. 197 pp. Georgia tidal creek. Trans. Am.
Fish. Soc. 114:821-825.
Bianchini, M., P. W. Sorensen, and H.
E. Winn. 1982. Stima dell'abbon- Crane, J. S., and A. G.. Eversole.
danza e schemi di movimento a breve 1980. Ectoparasitic fauna of glass raggio della anguilla Americana, eel and elver stages of American eel Anguilla rostrata (LeSueur) (Pisces, (Anguilla rostrata). Proc. World Apodes), nel Narrow River, Rhode Maricult. Soc. 11:275-280.
Island, USA. Naturalista Siciliano, S. IV, VI (Suppl.) 2:269-277.
(Translation provided by P. W. Crane, J. S., and A. G. Eversole.
Sorensen). 1981. Helminth parasites of Ameri-can eels from brackish water. Proc.
Bieder, R. C. 1971. Age and growth Annu. Conf. Southeast. Assoc. Fish of the American eel, Anouilla Wildl. Agencies 35:355-364.
21
Crane, J. S., and A. G. Eversole. Edel, R. K. 1975. The effect of In press. Metazoan ectoparasitic shelter availability on the activity fauna of American eels from brackish of male silver eels. Helgol. wiss.
water. Proc. Annu. Conf. Southeast. Meeresunters. 27:167-174.
Assoc. Fish Wildl. Agencies 39.
Edel, R. K. 1976. Activity rhythms of Creutzberg, F. 1959. Discrimina- maturing American eels (Anquilla tion between ebb and flood tide in rostrata). Mar. Biol. (Berl.) 36:
migrating elvers (Anguilla vulgaris 283-289.
Turt.) by means of olfactory percep-tion., Nature (Lond.) 184:1961-1962. Edel, R. K. 1979. Locomotor activity of female silver eels (Anguilla Creutzberg, F. 1961. On the orienta- rostrata) in response to shelter and tion of migrating elvers (Anguilla unnatural photoperiods. Rapp. P.-V.
vulgaris Turt.) in a tidal area. Reun. Cons. Int. Explor. Mer 174:
Netherlands J. Sea Res. 1:257-338.98-103.
Deelder, C. L. 1958. On the behavior Ege, V. 1939. A revision of the of elvers (Anguilla vulgaris Turt.) genus Anguilla Shaw: a systematic, migrating from the sea into fresh phylogenetic and geographical study.
water. J. Conserv. 24:135-146. Dana Rep. Carlsberg Found. No. 16.
256 pp.
Deelder, C. L. 1976. The problem of the supernumary zones in otoliths of Egusa, S. 1979. Notes on the culture the European eel (Anguilla anguilla of the European eel (Arguilla (Linnaeus, 1758)); a suggestion to anguilla L.) in Japanese eel-farming cope with it. Aquaculture 9:373- ponds. Rapp. P.-V. Reun. Cons. Int.
379. Explor. Mer 174:51-58.
Dolan, J. A., and G. Power. 1977. Eldred, B. 1971. First records of Sex ratio of American eels, Anguilla Anguilla rostrata larvae in the Gulf rostrata, from the Matemak River of Mexico and Yucatan Straits. Fla.
system, Quebec, with remarks on Dep. Nat. Resour. Mar. Res. Lab.
problems in sexual identification. Leafl. Ser. 4:1-3.
J. Fish. Res. Board Can. 34:294-299.
Facey, D. E. 1980. Food habits, age Dow, R. L. 1982. The Atlantic eel and growth, and sex ratio of Ameri-(Anguilla rostrata) fishery of can eels in Lake Champlain, Vermont.
Maine. Pages 43-47 in K. H. Loftus, M.S. Thesis. University of Vermont, ed. Proceedings of the 1980 North Burlington, Vt. 35 pp.
American eel conference. Ontario Fish. Tech. Rep. Ser. No. 4. Facey, D. E., and G. S. Helfman. In Ontario Ministry of Nat. Resour. press. Reproductive migrations of Toronto. American eels in Georgia. Proc.
Annu. Southeast. Assoc. Fish Wildl.
Agencies 39.
Eales, J. G. 1968. The eel fish-eries of eastern Canada. Bull. Facey, D. E., and G. W. LaBar. 1981.
Fish. Res. Board Can. 166. 79 pp. Biology of American eels in Lake Champlain, Vermont. Trans. Am. Fish.
Easley, J. E., Jr., and J. N. Freund. Soc. 110:396-402.
1977. An economic analysis of eel farming in North Carolina. N.C. Fahay, M. P. 1978. Biological and State Univ. Sea Grant Publ. UNC-SG- fisheries data on American eel, 77-16, Raleigh. 21 pp. Anguilla rostrata (LeSueur). U. S.
22
Natl. Mar. Fish. Serv. Tech. Ser. Haro, A. J. 1986. Pigmentation, Rep. No. 17, Northeast Fisheries size, and migration of el-vers Center, Highlands, N.J. 82 pp. (Anguilla rostrata) in a coastal Rhode Island stream. Common strat-Ford, T., and E. Mercer. 1986. Den- egies of anadromous and catadromous sity, size distribution, and home fishes. An international symposium.
range of American eels, Anguilla Boston, Mass. (Abstr.)
rostrata, in a Massachusetts salt march. Environ. Biol. Fishes 17: Harrell, R. M., and H. A. Loyacano, 309-314. Jr. 1980. Age, growth and sex ratio of the American eel in the Gray, R. W., and C. .W.Andrews. 1970. Cooper River, South Carolina. Proc.
Sex ratio of the American eel Annu. Conf. Southeast. Assoc. Fish.
(Anguilla rostrata (LeSueur)) in Wildl. Agencies 34:349-359.
Newfoundland waters. Can. J. Zool.
48:483-487. Helfman, G. S. 1986. Diel distribu-tion and activity of American eels Gray, R. W., and C. W. Andrews. 1971. in a cave-spring. Can. J. Fish.
Age and growth of the American eel Aquat. Sci. 43:1595-1605.
(Anguilla rostrata (LeSueur)) in Newfoundland waters. Can. J. Zool. Helfman, G. S., and J. B. Clark.
49:121-128. 1986. Rotational feeding: over-coming gape-limited foraging in Godfrey, H. 1957. Feeding of eels in anguillid eels. Copeia 1986:679-685.
four New Brunswick salmon streams.
Prog. Rep. Atlantic Coast Stn. 67: Helfman, G. S., D. L. Stoneburner, E.
19-22. L. Bozeman, P. A. Christian, and R.
Whalen. 1983. Ultrasonic telemetry of American eel movements in a tidal Gunning, G. E., and C. R. Shoop. creek. Trans. Am. Fish. Soc. 112:
1962. Restricted movements of the 105-110.
American eel, Anguilla rostrata (LeSueur), in freshwater streams with . comments on growth rate. Helfman, G. S., E. L. Bozeman, and E.
Tulane Stud. Zool. 9:265-272. B. Brothers. 1984a. Size, age, and sex of American eels in a Georgia Haedrich, R. L., and P. T. Polloni. River. Trans. Am. Fish. Soc. 113:
1978. Eels in Cape Cod waters. 132-141.
Pages 1-4 in 0. Ross, ed. Woods Hole Oceanographic Institute Sea Helfman, G. S., E. L. Bozeman, and E.
Grant Annual Report, 1.977-1978. B. Brothers. 1984b. Comparison of Woods Hole, Mass. American eel growth rates from tao returns and length-age analyses.
U.S. Natl. Mar. Fish. Serv. Fish.
Hanek, G., and K. Molnar. 1974. Bull. 82:519-522.
Parasites of freshwater ard anadro-mous *fishes from Matamek River Helfman, G. S., D. E Facey, L. S.
system, Quebec. J. Fish. Res. Board Hales, and E. L. Bozeman. In press.
Car. 31:1135-1139. The life history strategy of the American eel. Trans. Am. Fish.
Hansen, R. A., and A. G. Eversole. Soc.
1984. Age, growth, and sex ratio of American eels in brackish-water Hill, L. J. 1969. Reactions of the portions of a South Carolina River. American eel to dissolved oxygen Trans. Am. Fish. Soc. 113:744-749. tensions. Tex. J. Scif 20:305-313.
23
Hinton, M. J., and A. G. Eversole. in New England and Middle Atlantic 1978. Toxicity of ten commonly used estuaries. Limnol. Oceanogr. 5:338-chemicals to American eels. Proc. 340.
Annu. Conf. Southeast. Assoc. Fish Wildl. Agencies 32:599-604. Johnson, J. S. 1974. Sex distribu-tion and age studies. of Anguilla Hinton, M. J. and A. G. Eversole. rostrata (American eel) in fresh 1979. Toxicity of ten chemicals waters of the Delaware River. .M.S.
commonly used in aquaculture to the Thesis. East Stroudsburg State black eel stage of the American eel. College, East Stroudsburg, Pa. 57 Proc. World Maricult. Soc. 10:554- PP.
560.
Karlsson, L., G. Ekbohm, and G. Stein-Hinton, M. J., and A. G. Eversole. holtz. 1984. Comments on a study 1980. Toxicity and tolerance of the therma 1 behaviour of the studies with yellow-phase eels. American eel (Arguilla rostrata)
Prog. Fish-Cult. 42:201-203. and some statis tical suggestions for temperature preference studies.
Holmberg, B. and R. L. Saunders. Hydrobiologia 109:75-78.
1979. The effects of pentachloro-phenol on swimming performance and Keefe, S. G. 1982. The American eel oxygen consumption in the American (Anguilla rostrata) fishery in the eel (Anguilla rostrata). Rapp. P.-V. commercial waters of North Carolina.
Reun. Cens. Int. Explor. Mer 174: Pages 50-51 in K. H. Loftus, ed.
144-149. Proceedings of the 1980 North American eel conference. Ontario Hornberger, M. L. 1978. Coastal Fish. Tech. Rep. Ser. No. 4. Ontario Plains American eel study. Pages Ministry of Nat. Resour., Toronto.
42-50 in Progress report for October 1977 through January 1978. Kleckner, R. C., and W. H. Kruger.
South Carolina Wildlife and Marine 1981. Changes in swim bladder Research Department, Charleston. retial morphology in Anguilla rostrata during premigration meta-Hornberger, M. L., J. S. Tuten, A. morphosis. J. Fish Biol. 18:569-Eversole, J. Crane, R. Hansen, and 577.
M. Hinton. 1978. American eel investigations. Completion report Kleckner, R. C., and J. D. McCleave.
for March 1977-July 1978. South 1982. Entry of migrating American Carolina Wildlife and Marine eel leptocephali intc the Gulf Research Department, Charleston, and Stream system. Helgol. Wiss.
Clemson University, Clemson. 311 pp. Meeresunters. 35:329-339.
Hulet, W. H., J. Fischer, and B.
Rietberg. 1972. Electrolyte com- Kleckner, R. C., and J. D. McCleave.
position of anguilliform lepto- 1985. Spatial and temporal distri-cephali from the Straits of bution of American eel larvae in Florida. Bull. Mar. Sci. 22:432-448. relation to North Atlantic Ocean current systems. Dana 4:67-92.
Hurley, D. A. 1972. The American eel (Anguilla rostrata) in eastern Lake Kleckner, R. C., J. D. McCleave, and Ontario. J. Fish. Res. Board Can. G. S. Wippelhauser. 1983. Spawn-29:535-543. ing of American eel, Anguilla rostrata, relative to thermal Jeffries, H. P. 1960. Winter occur- fronts in the Sargasso Sea.
rences of Anguilla rostrata elvers Environ. Biol. Fishes 9:289-293.
24
Koehn, R. K., and G. C. Williams. McCleave, J. D., and R. C. Kleckner.
1978. Genetic differentiation with- 1982. Selective tidal stream out isolation in the American eel, transport in the estuarine migra-Anguilla rostrata. II. Temporal tion of glass eels of the American stability of geographic patterns. (Anguilla rostrata). J. Cons. Int.
Evolution 32:624-637. Explor. Mer. 40:262-271.
Kolenosky, D. P., and M. J. Hendry. McCleave, J. D., and R. C. Kleckner.
1982. The Canadian Lake Ontario 1985. Oceanic . migrations of fishery for American eel (Anguilla Atlantic eels (Anguilla spp.):
rostrata). Pages 8-16 in K. H. adults and their offspring.
Loftus, ed. Proceedings of the 1980 Contrib. Mar. Sci. 27:316-337.
North American eel conference.
Ontario Fish. Tech. Rep. Ser. No. 4, McCleave,. J. D., and G. W. Wippel-Ontario Ministry of Nat. Resour. hauser. 1986. Behavioral aspects Toronto. of selective tidal stream transport in juvenile American eel (Anguilla rostrata). Common strategies of Komourdjian, M. P., W. C. Hulbert, J. anadromous and catadromous fishes.
C. Fenwick, and T. W. Moon. 1977. An international symposium. Boston, Description and first occurrence of Mass. (Abstr.)
Myxidium zealandicum (Protozoa:
Myxosporidia) in the, North American McCleave, J. D., R. C. Kleckner, and eel Anguilla rostrata LeSueur. Can. M. Castonguay. 1986. Reproductive J. Zool. 55:52-59. sympatry of American and European eels and implications for migration LaBar, G. W., and D. E. Facey. 1983. and taxonomy. Common strategies of Local movements and inshore popula- anadromous and catadromous fishes.
tion sizes of American eels in Lake An international symposium. Boston, Champlain, Vermont. Trans. Am. Mass. (Abstr.)
Fish. Soc. 112:111-116.
McCord, J. W. 1977. Food habits and Liew, P. K. L. 1982. Impact of the elver migration of American eel, eel ladder on the upstream migrating Anguilla rostrata, (LeSueur), in eel (Anguilla rostrata) population Cooper River, South Carolina. M.S.
in the St. Lawrence River at Corn- Thesis. Clemson University, wall: 1974-1978. Pages 17-21 in K. Clemson, S.C. 47 pp.
H. Loftus, ed. Proceedings of the 1980 North American eel conference. Michener, W. K. 1980. Age, growth, Ontario Fish. Tech. Rep. Ser. No. 4, and sex ratio of the American eel, Ontario Ministry of Nat. Resour. Anguilla rostrata (LeSueur), from Toronto. Charleston Harbor, South Carolina.
M.S. Thesis. Clemson University, Clemson, S.C. 49 pp.
Marcy, B. C., Jr. 1973. Vulner-ability and survival of young Con- Miles, S. G. 1968. Laboratory exper-necticut River fish entrained at a iments on the orientation of the nuclear power plant. J. Fish. Res. adult American eel, Anguilla Board Can. 30:1195-1203. rostrata. J. Fish. Res. Board Can.
25,:2143-2155.
McCleave, J. D., and S. M. Fried.
1975. Nighttime catches of fishes Ogden, J. C. 1970. Relative abun-in a tidal cave in Montsweaq Bay dance, food habits, and age of the near Wiscasset, Maine. Trans. Am. American eel, Anguilla rostrata Fish. Soc. 104:30-34. (LeSueur), in certain New Jersey 25
streams. Trans. Am. Fish. Soc. the floor of the Atlantic in the 99:54-59. Bahamas. Bull. Mar. Sci. 29:401-405.
Pacheco, A. L., and G. C. Grant.
1973. Immature fishes associated Rommel, S. A., Jr., and A. B. Stasko.
with larval Atlantic menhaden at 1973. Electronavigation by eels.
Indian River Inlet, Delaware, Sea Frontiers 19:219-223.
1958-61. Pages78-117 in A. L.
Pacheco, ed. Proceedinqs of a work- Rupp, R. S., and S. E. DeRoche. 1965.
shop on egg, larval, and juvenile Standing crops of fishes in three stages of fish in Atlantic coast small lakes compared with 14C esti-estuaries. Middle Atlantic Coastal mates of net primary productivity.
Fish. Cen. Tech. Publ. No. 1. Trans. Am. Fish. Soc. 94:9-25.
Parsons, J., K. U. Vickers, and Y. Schmidt, J. 1913. First report on Warden. 1977. Relationship between eel investigations 1913. Rapp.
elver recruitment and changes in the P.-V. Reun. Cons. Int. Explor. Mer.
sex ratio of silver eels Anguilla 18:1-30.
anguilla L. migrating from Lough Neagh, Northern Ireland. J. Fish Schmidt, J. 1923. The breeding Biol. 10:211-229. places of the eel. Philos. Trans.
R. Soc. Lond. B. Biol. Sci. 211:179-Polloni, P. T., R. L. Haedrich, and C. 208.
M. Cetta. 1980. Resident eel popu-lations in Greater Sippewissett Schmidt, J. 1925. The breeding marsh and Herring river, Falmouth, places of the eel. Smithson. Inst.
Massachusetts, U.S.A. Massachusetts Annu. Rep. 1924:279-316.
Sea Grant Report. Office of Sea Grant. Woods Hole Oceanographic Seymour, N. R. 1974. Great black-Institution, Woods Hole, Mass. backed gulls feeding on live eels.
Can. Field-Nat. 88:352-353.
Poluhowich, J. J. 1972. Adaptive significance of eel multiple hemo- Sheldon, W. W. 1974. Elvers in globins. Physiol. Zool. 45:215-222. Maine; techniques of locating, catching, and holding. Maine Power,. J. H., and J. D. McCleave. Department of Marine Resources, 1983. Simulation of the North Augusta, Me. 27 pp.
Atlantic ocean drift of Anquilla leptocephali. U.S. Natl. Mar. Fish. Sinha, V. R. P., and J. W. Jones.
Serv. Fish. Bull. 81:483-500. 1967. On the food of the freshwater eels and their feeding relationship Ricker, F. W. 1976. American eel with salmonids. J. Zool. (Lond.)
(Anguilla rostrata) management plan. 153:119-137.
Maine Dep. Mar. Resour. Sect. 4 Complet. Rep. Project No. AFSC-13/ Smith, D. G. 1968. The occurrence of FWAC-2. 17 pp. larvae of the American eel, Anguilla rostrata, in the Straits of Florida Ricker, F. W., and T. Squiers. 1974. and nearby areas. Bull. Mar. Sci.
Spring elver survey: Pilot project. 18:280-293.
Maine Department of Marine Resources, Augusta, Me. 11 pp. Smith, M. W., and J. W. Saunders.
1955. The American eel in certain Robins, C. R., D. M. Cohen, and C. H. fresh waters of the Naritime Robins. 1979. The eels, Anguilla Provinces of Canada. J. Fish. Res.
and Histiobranchus, photographed on Board Can. 12:238-269.
26
Sorensen, P. W. 1986. Origins of the United States Department of Commerce.
freshwater attractant(s) of migrat- 1981. Fisheries of the United ing elvers of the American eel, States, 1980. U.S. Natl. Mar. Fish.
Anquilla rostrata. Environ. Biol. Serv. Curr. Fish. Stat. No. 8100.
Fishes 17:185-200.
United States Department of Commerce.
Sorensen, P. W., and M. L. Bianchini. 1984. Fishery statistics of the 1986. Environmental correlates of United States - 1977. U.S. Natl.
the freshwater migration of elvers Mar. Fish. Serv. Stat. Digest of. the American eel in a Rhode No. 71.
Island brook. Trans. Am. Fish. Soc.
115:258-268. Vladykov, V. D. 1955. Eel fishes of Quebec. Quebec Dep. Fish. Album No.
Stasko, A. B., and S. A. Rommel, Jr. 6:1-12.
1977. Ultrasonic tracking of Atlantic salmon and eels. Rapp. Vladykov, V. D. 1964. Quest for the P.-V. Reun. Cons. Int. Explor. Mer. true breeding area of the American 179:36-40. eel (Anguilla rostrata LeSueur). J.
Fish. Res. Board Can. 21:1523-1530.
Stearns, S. C., and R. E. Crandall.
1984. Plasticity for age and size Vladykov, V. D. 1966. Remarks on the at sexual maturity: a life history American eel (Anquilla rostrata response to unavoidable stress. LeSueur). Sizes of elvers entering Paces 13-33 in G. W. Potts and R. J. streams; the relative abundance of Wooton, eds. Fish reproduction: adult males and females; and present strategies and tactics. Academic economic importance of eels in North Press, New York. America. Verh. Int. Verein. Theor.
Angew. Limnol. 16:1007-1017.
Sykes, D. P. 1981. Migration and development of young American eels, Anguilla rostrata, in coastal North Vladykov, V. D. 1973. Macrophthalmia Carolina. N.C. State Univ. Sea in the American eel (Anguilla Grant Working Pap. 81-5, Raleigh. rostrata). J. Fish. Res. Board Can.
34 pp. 30:689-693.
Tesch, F. W. 1977. The eel. J. Vladykov, V. D., and H. March. 1975.
Greenwood, translator. Chapman and Distribution of leptochephali of the Hall, London. 422 pp. two species of Anguilla in the western North Atlantic based on Tongiorgi, P., L . Tosi, and M. Bal- collections made between 1933 and samo. 1986. Thermal preferences in 1968. Syllogeus 6:1-38.
upstream migrating glass-eels of Anguilla anguilla (L.). J. Fish Walsh, P. J., G, D. Foster, and T. W.
Biol. 28:501-510. Moon. 1983. The effects of tem-perature on metabolism of the United States Department of Commerce. American eel Anguilla rostrata 1980a. Massachusetts landings, (LeSueur): compensation in the annual summary 1979. U.S. Natl. summer and torpor in the winter.
Mar. Fish. Serv. Curr. Fish. Stat. Physiol. Zool. 56:532-540.
No. 8010.
Wenner, C. A. 1973. Occurrence of United States Department of Commerce. American eels, Anguilla rostrata, in 1980b. Maine landings, annual water overlying the eastern North summary 1979. U.S. Natl. Fish. American Continental Shelf. J.
Serv. Curr. Fish. Stat. No. 8009. Fish. Res. Board Can. 30:1752-1755.
27
Wenner, C. A., and J. A. Musick. Winn, H. E., W. A. Richkus, and L. K.
1974. Fecundity and gonad obser- Winn. 1975. Sexual dimorphism and vation of the American eel, natural movements of the American Anguilla rostrata, migrating from eel (Anguilla rostrata) in Rhode Chesapeake Bay, Virginia. J. Fish. Island streams and estuaries.
Res. Board Can. 31:1387-1391. Helgol. Wiss. Meeresunters. 27:167-174.
Wenner, C. A., and J. A. Musick.
1975. Food habits and seasonal abundance of the American eel, Wippelhauser, G. S., J. D. McCleave, Anguilla rostrata, from the lower and R. C. Kleckner. 1985. Anguilla Chesapeake Bay. Chesapeake Sci. rostrata leptocephali in The Sar-16:62-66. gasso Sea during February and March 1981. Dana 4:93-98.
Williams, G. C., and R. K. Koehn.
1984. Population genetics of North Atlantic catadromous eels Yamamoto, K., and.K. Yamauchi. 1974.
(Anguilla). Pages 529-560 in B.J. Sexual maturation of Japanese eel Turner, ed. Evolutionary genetics and production of eel larvae in the of fishes. Plenum Press, New York, aquarium. Nature (Lond.) 251:220-N.Y. 222.
28
10272-t!a REPIORT OOCUMENTATION 1. *EPoRT NO. R#Cinilres Accession No.
PAGE Biological Report 82(11.74)*l
- 4. Title* an dSutite Report Date Species Profiles: Life Histories and Environmental Requirements August 1987 of Coastal Fishes and Invertebrates (North Atlantic)--American Eel .
- 7. A ~ *54~) Pedorml "allnimation Root. m.
Douglas E. Facey and Michael J. Van Den Avyle
- 4. Performing Organ*z*tion Name and Address 311 ProiectfTesk/Work Unit No.
Georgia Cooperative Fish and Wildlife Research Unit School of Forest Resources It.oC Ge(G) No.
University of Georgia (C)
Athens, GA 30602 1L Sponsoring Organization Name end Address (G)
National Wetlands Research Center U.S. Army Corps of Engineers IL TypeofRepo*&Period C&ed Fish and Wildlife Service Waterways Experiment Station U.S. Department of the Interior P.O. Box 631 Washington, DC 20240 Vicksburg, MS 39180 14.
- 15. Supplementary Note
- U.S. Army Corps of Engineers Report No. TR EL-82-4
.141.Abstract (Umlt: 200 words)
Species profiles are literature summaries of taxonomy, life 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 10712 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, salinity, 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.
- 17. Document Anlyseis 0. Descriptors Estuaries Life cycles Contaminants Fisheries Growth Animal migrations Salinity Oxygen Aquaculture Temperatures
- b. lde*tlflemr/OpenýEndd Terms Anguilla rostrata Catadromous fishes Life history Environmental requirements
- c. COSATI Field/Group I& Aýellabillty Statement Unlimited distribution (So. ANSI-M39.18)
Depertment of Commerce
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 enjoy-ment 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 Depart-ment 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 FISH AND WILDLIFE SERVICE TAKE PRIDE, in America UNITED STATES DEPARTMENT OF THE INTERIOR FISH AND WILDLIFE SERVICE National Wetlands Research Center NASA-Slidell Computer Complex 1010 Gause Boulevard Slidell, LA 70458