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LibraryNational Wetlands Research Center
1 U. S. Fish and Wildlife Service
QL155.S63no.82-11.24
FWSIOBS-82111.24 Lafayetie, La. 7OgO6July 1984 7
Species Profiles: Life Histories andEnvironmental Requirements of Coastal Fishesand Invertebrates (South Atlantic)
TR EL-82-4
AMERICAN EEL
/
Fish and Wildlife ServiceCoast al Ecology Group
Waterways Experiment StationU.S. Department of the Interior U.S. Army Corps of Engineers
.-- -
FWS/OBS-82/11.24TR EL-82-4July 1984
Species Profiles: Life Histories and EnvironmentalRequirements of Coastal Fishes and Invertebrates (South Atlantic)
AMERICAN EEL
Michael J. Van Den AvyleGeorgia Cooperative Fishery Research Unit
School of Forest ResourcesUniversity of Georgia
Athens, GA 30602
Project ManagerLarry ShanksProject OfficerNorman Benson
National Coastal Ecosystems TeamU. S. Fish and Wildlife Service
1010 Gause BoulevardSlidell, LA 70458
This study was performed forCoastal Ecology Group
U.S. Army Corps of EngineersWaterways Experiment Station
Vicksburg, MS 39180
and
National Coastal Ecosystems TeamDivision of Biological Services
Research and DevelopmentFish and Wildlife Service
U.S. Department of the InteriorWashington, DC 20240
This series should be referenced as follows:
U.S. Fish and Wildlife Service. 1983-19 Species profiles: life historiesand environmental requirements of coasta'fishes and invertebrates. U.S. FishWildl. Serv. FWS/OBS-82/11. U.S. Army Corps of Engineers, TB EL-82-4.
This profile should be cited as follows:
Van Den Avyle, M. J. 1984. Species profiles: life histories and environmentalrequirements of coastal fishes and invertebrates (South Atlantic) -- Americaneel. U.S. Fish Wildl. Serv. FWS/OBS-82/11.24. U.S. Army Corps of Engineers,lR EL-82-4. 20 pp.
PREFACE
This species profile is one of a series on coastal aquatic organisms,principally fish, of sport, commercial, or ecological importance. The profilesare designed to provide coastal managers , engineers, and biologists with a briefcomprehensive sketch of the biological characteristics and environmental require-ments of the species and to describe how populations of the species may beexpected to react to environmental changes caused by coastal development. Eachprofile has sections on taxonomy, life history, ecological role, environmentalrequirements, and economic importance, if applicable. A three-ring binder isused for this series so that new profiles can be added as they are prepared. Thisproject is jointly planned and financed by the U.S. Army Corps of Engineers andthe U.S. Fish and Wildlife Service.
Suggestions or questions regarding this report should be directed to:
Information Transfer SpecialistNational Coastal Ecosystems TeamU.S. Fish and Wildlife ServiceNASA-Slide11 Computer Complex1010 Gause BoulevardSlidell, LA 70458
or
U.S. Army Engineer Waterways Experiment StationAttention: WESERPost Office Box 631Vicksburg, MS 39180
iii
CONTENTS
Page
PREFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iiiCONVERSION TABLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . \:ACKNOWLEDGMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi
NOMENCLATURE/TAXONOMY/RANGE . . . . . . . . . . . . . . . . . . . . . . . . 1MORPHOLOGY/IDENTIFICATION AIDS . . . . . . . . . . . . . . . . . . . . . .REASON FCR INCLUSION IN SERIES . . . . . . . . . . . . . . . . . . . . . . :LIFEHISTORY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Spawning ................................ iLarval (Leptocephalus) Stage ...................... 5GlassEel Stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . .ElverStage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
z
Yellow Eels and Silver Eels ....................... 7GROWTH CHARACTERISTICS ..........................COMMERCIAL AND SPORT FISHERIES . . . . . . . . . . . . . . . . . . . . . .
;
ECOLOGICAL ROLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .ENVIRONMENTAL REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . . . .
'1;
Temperature ...............................Salinity ................................
:;
Dissolved Oxygen ............................Habitat Structure ............................
‘1;
River and Tidal Currents ........................ 13Contaminants . . . . . . . . . . . . . . . . . . . . . . . . . . 13Environmental Fait;& and Sex Determination ............... 14
LITERATURE CITED ............................. 15
iv
Multiply !!Y To Obtain
millimeters (mm)centimeters (cm)meters (m)kilometers (km)
square meters (m2)square kilometers (km2)hectares (ha)
0.03937 inches0.3937 inches3.281 feet0.6214 miles
10.76 square feet0.3861 square miles2.471 acres
liters (1)cubic meters (m3)cubic meters
0.2642 gallons35.31 cubic feet0.0008110 acre-feet
milligrams (mg) 0.00003527 ouncesgrams (9) 0.03527 ounceskilograms (kg) 2.205 poundsmetric tons (t) 2205.0 poundsmetric tons 1.102 short tonskilocalories (kcal) 3.968 British thermal units
Celsius degrees 1.8(CP) + 32 Fahrenheit degrees
inchesinchesfeet (ft)fathomsmiles (mi)nautical miles (nmi)
square feet (ft2)acressquare miles (mi2)
25.40 millimeters2.54 centimeters0.3048 meters1.829 meters1.609 kilometers1.852 kilometers
0.0929 square meters0.4047 hectares2.590 square kilometers
gallons (gal)cubic feet (ft3)acre-feet
3.785 liters0.02831 cubic meters
1233.0 cubic meters
ounces (oz) 28.35pounds (lb) 0.4536short tons (ton) 0.9072British thermal unit (Btu) 0.2520
Fahrenheit degrees 0.5556(F"
CONVERSION FACTORS
Metric to U.S. Customary
U.S. Customary to Metric
V
32)
gramskilogramsmetric tonskilocalories
Celsius degrees
ACKNOWLEDGMENTS
Dr. Gene Helfman, Earl Bozeman, and Doug Facey, University of Georgia, andDr. Arnold G. Eversole, Clemson University, reviewed earlier drafts of thisSpecies Profile and provided current information that otherwise could not havebeen included.
vi
Figure 1. American eel.
AMERICAN EEL
NOMENCLATURE/TAXONOMY/RANGE
Scientific namePreferred common Aame
Anguilla rostrata. . . American
eel (Figure 1)Other common names . . . . . Anauille.
3;: 1t
ee 1Class .Order .Family
low eel, green eel, blazk eel;t l e e e l , bronze eel, glass, silver eel, river eel. . . . . . . . . Osteichthyes. . . . . . . . Anguilliformes. . . . . . . . . Anguillidae
Geographic range: Adultsdevelopmental stagesfreshwater rivers,waters, and the openthe southern tip of
or variousoccur in
coastalocean fromGreenland,
Labrador, and Newfoundland south-ward along the Atlantic coast ofNorth America, into the Gulf ofMexico as far as Tampico, Mexico,and in Panama, the Greater andLesser Antilles, and southward tothe northern portion of the east;;;;i of South *America (Tesch
. The species is abundantfrom Maine to Mexico, is resident
in the Mississippi Valley, andoccurs in the West Indies andBermuda (Figure 2). Bertin(1956) reported the latitudinalrange for the American eel as 5"to 62" N. It occurs in warmbrackish and freshwater streams,estuaries, and coastal rivers.The American eel sometimes occursin cold freshwater trout streamsin mountainous regions. Adultsare occasionally found in land-locked lakes, primarily in theNortheastern United States. Itsdistribution has increasedbecause of its hardiness and theease with which it can be trans-planted into new habitats.
MORPHOLOGY/IDENTIFICATION AIDS
American eels undergo a series ofmorphological changes in their lifecycle; these characteristics arepresented in the LIFE HISTORY section.The following material was summarizedprimarily from Fahay (1978) and Tesch(1977).
I M I L E S
OII0 50 ii0
i K I L O M E T E R S I
Figure 2. Major rivers that support the American eel in the South AtlanticBight. Eels also are common in other freshwater tributaries, and in bays andestuaries.
2
The body is elongate and snake-like (Figure 1). The dorsal and analfins are confluent with the rudimen-tary caudal fin. Pectoral fins arepresent, but ventral (pelvic) fins areabsent. The body is covered by minuteembedded scales (often causing speci-mens greater than 3 to 5 years of ageto appear scaleless). The lateralline is well developed. The mouth isterminal; jaws contain bands of small,pectinate or setiform teeth. A longtooth patch also occurs on the vomer.The number of vertebrae ranges from103 to 111 but usually is 106 to 108(Schmidt 1913).
No other anguillid eels occur inNorth American coastal waters, but theAmerican eel's spawning grounds coin-cide closely with those of the Europe-an eel.(+nguilla anguilhla).E x t e r n a l -ly vlslb e traits of t e two specimensare similar; however, the European eelhas 111-119 vertebrae (mean = 115).Ege (1939) presented comprehensivemorphological data for A. rostrata.Some authors have argued That Europeanand American eels should be regardedas geographical variants of the samespecies, but this is not generallyaccepted at present (Fahay 1978).
No data are available thatconclusively point to geographic vari-ations in morphology, and no subpopu-lations have been distinguished.Koehn and Williams (1978) notedprotein differences among juvenileeels collected from different loca-tions along the Atlantic seaboard, butthey concluded that the differenceswere due to variations in selectivepressures among environments in whichgrowth occurred.
REASON FOR INCLUSION IN SERIES
The American eel supports valu-able commercial and limited recrea-tional fisheries throughout most ofits range. Harvested adults often areshipped alive or frozen to Europewhere they frequently are smoked
before marketing, and a fishery forelvers (immature eels typically lessthan 60 mm long) has recently begun inthe South Atlantic Bight. Elvers areshipped to Japan wherecultured in ponds.
they arePond rearing of
eels in the United States is in adevelopmental stage, and there is apotential for development and expan-sion of an eel culture industry.
The American eel is an importantprey species of larger marine andfreshwater fishes and is a predator ona variety of other animals includingcommercially important crabs andclams. Eels contribute to the loss ofnutrients from freshwater rivers andlakes because of their great organicintake, large numbers, lengthy stay infreshwater, and subsequent migrationto sea (Barila and Stauffer 1980).Alteration of river flow into estu-aries could affect upstream migrationof immature eels.
LIFE HISTORY
The life cycle of the Americaneel includes oceanic, estuarine, andriverine phases (Figure 3). Manydetails of its life history are onlygenerally understood or have beeninferred from knowledge of the conge-neric European eel. Little has beenreported on eel life history in riversalong the South Atlantic Bight; muchof the information presented below isbased on work in Middle and NorthAtlantic areas of the United Statesand Canada.
Different stages of the eel'slife cycle are known by a variety ofcommon names that are used throughoutthe scientific literature. The larvaeare called leptocephali (sing. =leptocephalus); they first metamor-phose into unpigmented "glass eels"that gradually develop pigmentationand are then called elvers. Elversmigrate into freshwater where theyremain several (sometimes many) yearsand are called yellow eels. Yellow
3
metamorphosis
/ .I SILVER EEL
metamorphosis
Figure 3. Diagrammatic representationof the American eel's life history.
eels may be sexually undifferentiated(gonads contain no definable gametes),hermaphroditic (oogonia .and spermato-gonia present), or sexually differen-tiated (females with oogonia; maleswith spermatogonia present), but noneof these stages are capable of repro-duction and, hence, all yellow eelsare immature. Maturation is accompa-nied by changes in body color andmorphology; maturing eels migratedownriver and through the ocean to thespawning grounds and are known as"bronze eels" or "silver eels."Details of life history for thesestages are provided below.
Spawning
The American eel is catadromous.It spawns in the sea but spends mostof its life in rivers, freshwaterlakes, and sometimes estuaries. Aftermaturity it returns to the sea (Fig-ure 3). The age at maturity has notbeen well defined; Fahay (1978) re-ported that maturation occurred beyondage III for males and at age IV-VIIfor females fran northerly popula-tions, but recent data suggest thatmaturation is more rapid in popula-tions along the South Atlantic Bight.
Helfman and Bozeman (unpublished MS:l)collected sexually differentiatedmales and females at age III2 in theAltamaha River, Georgia, and concludedthat females there may have matured atearlier ages and smaller sizes thaneels in northern areas whereas malesmatured at the same age and size asnorthern eels. Hansen and Eversole(in press) and Harrell and Loyacano(1980) collected differentiated malesand females as young as age II andIII, respectively, in the CooperRiver, South Carolina.
Prior to seaward migration in thefall, maturing eels begin a metamor-phosis into the silver eel stage, asdescribed in the Yellow and SilverEels section.
Eels migrating from ChesapeakeBay are in a more advanced state ofmetamorphosis than those migratingfrom Canadian waters; this supposedlyenables eels to reach the southerlyspawning grounds in relatively similarstages of maturity (Wenner and Musick1974). The difference in the extentof metamorphosis between migratingeels from Canada and Chesapeake Baysuggests that migrating eels in SouthAtlantic rivers could be even furtherdeveloped than those in Chesapeake Bayat the outset of migrations. Helfmanand Bozeman (unpublished MS?) conclud-ed that reproductive migrations fromthe Altamaha River, Georgia, occurredduring late winter or early spring,but Hansen and Eversole (in press) andMichener (1980) indicated that migra-tions occurred during the fall in theCooper River, South Carolina.
'Population attributes of Ameri-can eels in a Georgia river. G. S.Helfman and E. L. Bozeman, Departmentof Zoology and Institute of Ecology,University of Georgia, Athens, GA30602. Submitted to Trans. Am. Fish.sot.
21n this case, age is the numberof years spent in freshwater (see theGROWTH CHARACTERISTICS section foraging methods).
d
d
Few details are known about theoceanic spawning migration of theAmerican eel. The first collectionsof adults in offshore waters werereported by Wenner (1973) in the openocean southeast of Cape Cod, Massachu-setts, east of Assateague Island,North Carolina, and southeast ofChesapeake Bay. The means by whicheels navigate to spawning grounds arepoorly understood. Miles (1968)concluded that the eel was capable ofnoncelestial orientation (southward),and Rommel and Stasko (1973) indicatedthat eels may use geoelectric fieldsgenerated by ocean currents to navi-gate. Robins et al. (1979) photo-graphed two adult Anguilla eels on thefloor of the Atlantic Ocean in theBahamas at depths of about 2000 m, andalthough it was impossible to deter-mine if the specimens were European orAmerican eels, the authors believedthem to be prespawning A. rostrata.
Stasko and Rommel (1977) trackedfive migrating eels in the lower St.Croix River Estuary, New Brunswick,Canada and found that one eel moved25 km i'n 20 hr and another moved 38 kmin 40 hr. Eels they studied showedconsiderable vertical movements in thewater column; behavior did not changewith die1 or tidal cycles. SilverEuropean eels traveled at 44 km perday when migrating to spawn (Tesch1977). Edel (1976) believed that thedepth at which American eels migratein the ocean varied with light inten-sity so that swimming depth would varywith turbidity of the water.
Spawning by American eels hasnever been directly observed, andspawning areas have been delineated onthe basis of collections of larvae.Spawning apparently occurs in theSargasso Sea as early as January orFebruary and may continue into August.Tesch (1977) summarized work bySchmidt (1923), Vladykov (1964), Smith(1968), and Vladykov and March (1975),and showed a spawning zone south ofBermuda and north of the Bahamas thatis centered at about 25“ N and 69" W.
The youngest stages of American eellarvae coexist with European eellarvae, but American eel larvae ore-dominate24" Nreportednot been
west of 62" W and south of(Fahay 1978). Fahay alsothat A. rostrata larvae havefound-east of 50' W.
The depth at which spawningoccurs is not known, but Taning (1938)reported that larvae collected nearBermuda occurred only at depthsbetween 550 and 2200 m. Egg diameterof A. rostrata is about 1.1 mm (Tesch1977). Incubation periods of Americaneel eggs are not known.
Fecundity is 10 to 20 millioneggs per female (Vladykov 1955, citedby Fahay 1978; Eales 1968). Relation-ships between eel size and fecundityfor 21 eels were reported by Wennerand Musick (1974) as:
log F = -4.29514 + 3.74418 log TL, orlog F = 3.2290 + 1.1157 log W;
Where F = number of eggs per female,TL = total length, mm, andW = total weight, g.
Adult eels presumably die afterspawning. None have been observed tomigrate up rivers, and occurrences ofspent eels have not been reported.
Larval (Leptocephalus) Stage
Hatching occurs from Februarythrough August (Vladykov and March1975; Fahay 1978), and the larvalstage lasts about 1 year or perhapslonger. The body is lanceolate inshape, sharply pointed at both ends,and deepest at the middle (see Tesch[1977] or Fahay [1978] for illustra-tions). The size at hatching has notbeen described, but Schmidt (1925)collected 7- to 8-mm larvae in Febru-ary. The smallest larvae collected byVladykov and March (1975) and Smith(1968) were 12 mm and 17 mm,respectively.
5
During the leptocephalus stage,the larvae grow and are transported byocean currents. Larvae collected bySchmidt (1925) were 7 to 8 mm long inFebruary, 20 to 25 mm in April, 30 to35 mm in June, 40 mm in July, 50 to 55mm in September, and 60 to 65 mm bythe end of the first year of life.The longest leptocephalus collected byVladykov and March (1975) was 69 mm.
Vladykov and March (1975) sug-gested that larval A. rostrata mayspend more than 1 year in the sea.Limited evidence also suggests thatsome eels remain in the leptocephalusstage for more than 1 year. Smith(l;;8)treported a. 50-mm leptocephalus
spawning grounds duringApril. This larva was too long tohave been spawned in the immediateseason (Fahay 1978).
The Northern Equatorial Currentand the Gulf Stream transport larvaenorthward along the eastern seaboardof North America. Sampling has shownthat larvae are abundant in theFlorida Straits and in the areabetween Bermuda and the Bahamas fromApril through August (Smith 1968), andEldred (1971) found A. rostrata lepto-cephali in the Gurf of Mexico andYucatan Straits, but mechanisms bywhich the larvae are dispersed intothe Gulf of Mexico and southward tothe coast of South America have notbeen determined.
Glass Eel Stage
During the pelagic phase, lepto-cephali reach a size and physiologicalstate at which they begin to metamor-phose. The early stages of this tran-sition involve: (1) shrinkage in sizeand weight, primarily due to a reduc-tion in water content; (2) changes inthe configuration of the head andjaws; and (3) accelerated developmentof the digestive system (Fahay 1978).After these changes occur, the eelsare similar in overall morphology toyellow eels, but they lack externalpigmentation and are called "glass
eels." Glass eels actively migratetoward land and freshwater, and asthey approach coastal areas, externalpigmentation develops and the bodybecomes uniformly dark brown. At thisstage, metamorphosis is complete andthe eel is now called an elver.
Elver Stage
Most elvers move into coastalareas, estuaries, and up freshwaterrivers in the late winter or earlyspring. Vladykov (1966) suggestedthat elvers generally arrive insouthern estuaries earlier and atsmaller sizes than in the north, butcatch records indicate considerableoverlap in the timing of shorewardmovements along the Atlantic coast.Such movements have occurred duringApril in Narragansett Bay and nearWashington, D.C.; February and Marchin Delaware; January in Long IslandSound and Rhode Island estuaries; offNova Scotia in April, and the Bay ofFundy in summer (Fahay 1978). In theSouth Atlantic, migrating elvers havebeen collected during January inFlorida and South Carolina and duringJanuary through May, with peak catchesin March and April, in North Carolina(SmithSykes
11996881;;Hornberger 1978, ci;;t,F;Sykes 1981).
moving into South Atlantic estuariesand rivers typically are 46 to 60 mmlong. Helfman and Bozeman (unpub-lished MS.3) collected 49- to 56-mmglass eels from the Altamaha RiverEstuary, Georgia, in late February;daily growth rings on the otolithsshowed 250 to 300 days of age.
Small numbers of elvers regularlyarrive in estuaries in the fall, andFahay (1978) suggested that these
3Growth rates of American eels ina Georgia estuary. G. S. Helfman andE. L. Bozeman, Department of Zoologyand Institute oLthF;slogy,of Georgia,Submitted to U.S. Nail.
GAUniv;;;;;y
Mar. Fish:Serv. Fish. Bull.
6
"early" arrivals may be the earliestspawned individuals or a segment ofthe main body of leptocephali that ismoved northward more quickly bylocalized water currents. Alterna-tively, these elvers may be "late"arrivals produced from leptocephalithat did not metamorphose during theprevious winter/spring.
Elvers occupy freshwater-salt-water transition areas before ascend-ing rivers. During this period,elvers are active at night and burrowor rest in deep water during the day(Deelder 1958). This nocturnalbehavioral pattern causes the elversto be transported upstream by floodtides that occur at night, and theydrift back down during ebb (Fahay1978). Pacheco and Grant (1973)reported similar patterns for elversat the mouth of the Indian River,Delaware, and Tesch (1977) notedequivalent behavior by European eelelvers. He also indicated that A.
\kanguilla elvers orient to rivercurrents for upstream movement, and ifthe current becomes too weak or toostrong (velocities not specified),eels may move into backwater areas,severely delaying upstream progress.Basic similarities in behavior ofEuropean and American eel elverssuggest that A. rostrata elvers wouldbe similarly-affected by extremelyfast or slow river currents.
Fahay (1978) stated that asupstream migration to freshwaterstreams begins, males tend to stay inbrackish water while females move intofresher water, but this is based onobserved distribution patterns ofolder eels rather than direct observa-tion of elver behavior. When elverscease their migration, they begin agrowth and differentiation period inwhich they are called yellow eels.
Yellow and Silver Eels
Many authors (e.g., Bigelow andSchroeder 1953; Vladykov 1966) have-stated that yellow eel females occur
primarily in freshwaters whereas malesare generally found in salt- or brack-ish waters.however,
Dolan and Power (1977),concluded that an extensive
review of literature did not supportthis "female-freshwater, male-salt-water" theory. Recent studies con-tinue to be inconsistent. Helfman andBozeman (unpublished MS3) found thatfemales represented 94% of the sexu-ally differentiated yellow eelscollected from freshwater areas ofthe Altamaha River in Georgia and 64%of the differentiated yellow eels inestuarine areas. However, collectionsof eels from the Cooper River, SouthCarolina, showed a minor variation ofsex ratio from fresh- to saltwater.Females contributed 97%, 95%, and 93%of the differentiated eels collectedfrom fresh-, brackish-, and saltwaterareas, respectively (Harrell andLoyacano 1980; Michener 1980; Hansenand Eversole, in press).
In addition to the freshwater-saltwater variation in the sex ratio,a geographic variation in the distri-bution of the sexes has been hypothe-sized. Vladykov (1966) stated thatmale eels predominate in middle andsouthern Atlantic populations (NewJersey to Florida) whereas femalespredominate from New York to Newfound-land. Work in the Cooper River, SouthCarolina, and the Altamaha River,Georgia (described in the precedingparagraph), however, does not supportthis hypothesis. Vladykov believedthat a latitudinal change in sexcomposition was related to the size-differences in elvers along the coast,and he said that smaller elversentering southern streams supposedlybecome males whereas the larger elversentering northern systems probablydevelop into females (see the ENVIRON-MENTAL REQUIREMENTS section foralternate explanations). As withfreshwater-saltwater variations in thesex ratio, Dolan and Power (1977)suggested that latitudinal variationswere not well documented. They statedthat the apparent geographic distribu-tion of sex in the American eel could
7
"be a result of incorrect sexing,selectivity of sampling gear and thepossible exclusion of smaller males,and the assumption that characteris-tics for the American eel wouldparallel those of the European eel.The gender of adult eels is not exter-nally apparent, and gonadal tissuesshould be examined histologically toavoid errors in sex determination(Dolan and Power 1977; Facey and LaBar1981).
Age at maturity and other aspectsof reproduction are described in theSpawning section. Sexual differentia-tion does not occur until eels reachabout 200 mm in length (Fahay 1978).Prior to completion of the differenti-ation process, some eels possessgonads containing male and femalegametes (juvenile hermaphroditism;Tesch 1977), but after gender isestablished, it does not change (Fahay1978). Helfman and Bozeman (unpub-lished MS.3) reported that differenti-ated and undifferentiated yellow eelsin the Altamaha River, Georgia, over-lapped considerably in size: undif-ferentiated eels were as large as 363mm at age VII; differentiated maleswere as small as 209 mm at age III;differentiated females were as smallas 186 mm at age III; and hermaphro-dites, which constituted less than 1%of the collections, ranged from 267 to328 mm at ages IV to V. Hansen andEversole (in press) reported similaroverlap in size and age of differenti-ated and undifferentiated eels in theCooper River, South Carolina.
Yellow eels begin to metamorphoseinto silver eels in the fall prior toseaward migration. The metamorphosisincludes: (1) color change (to ametallic, bronze-black sheen; pectoralfins change from yellow-green toblack); (2) fattening of the body; (3)thickening of the skin; (4) enlarge-ment of the eyes (macrophthalmia) andchanges in visual pigments in the eyein preparation for migrating at darkocean depths (Vladykov 1973; Beatty1975); (5) increased length of capil-
8
laries in the rete in the swim blad-der, which also may be an indicationof migrating at great depths (Klecknerand Kruger 1981); and (6) degenerationof the digestive tract. Silver(metamorphosed) eels appear to bebetter adapted to swimming than yelloweels (Holmberg and Saunders 1979).Presumably, ovaries mature fully onlyafter the migrating female reachessaltwater (Fahay 1978).
GROWTH CHARACTERISTICS
Larvae typically reach 40 to 70mm after 1 year of growth; Hornbergeret al. (1978) collected glass eelsfrom the Cooper River, South Carolina,from January through April that aver-aged 55 mm in length and ranged from45 to 65 mm (see the Larval Stagesection for growth within the firstyear). The metamorphosis into elversis accompanied by a decrease in lengthand weight due to reduction in watercontent of the body. Elvers growslowly and reach about 127 mm after cthe first year in freshwater (Bigelowand Schroeder 1953). Yellow eelstypically grow slowly but can achieveweights up to 6.8 kg; females caughtfrom the St. Lawrence River range from960 to 1270 mm long and 0.9 to 4.5 kg(Fahay 1978). Females typicallygrow to a larger size than males.
Eels have been aged from otolithsand scales. Otoliths in eels consistof a translucent nucleus (formed atsea) surrounded by broad opaque summerzones and narrow translucent winterzones (Harrell and Loyacano 1980).Harrell and Loyacano (1980) usedotoliths to age American eels from theCooper River in South Carolina.Distinct annuli were present in 410 of415 otoliths examined; the opaque ringfirst appeared in May and the translu-cent zone was first evident in Novem-ber. The third opaque ring corre-sponds to the eel's first growingseason in freshwater. Eels in Cana-dian waters formed their first scalesat 160 to 200 mm during their third to
fifth year of life and the scalesformed annual rings in subsequentwinters (Smith and Saunders 1955).Thus, in northerly areas, age in yearsgenerally will be the number of scalerings plus three. The eel, however,continues to form scales as it grows,leading to a situation in which dif-ferent scales from the same fish cangive different ages (Smith andSaunders 1955).
Growth rates within year classesare highly variable, leading to con-siderable variation in length at ageand poor predictability of age fromsize. Lengths of eels at various agesin northerly populations are summa-rized in Table 1. Few growth data foreels in South Atlantic States havebeen reported.(1980)
Harrell and Loyacanoreported that eels in the
Cooper River grew 45 to 52 mm per yearfor ages II-XVI. Helfman and Bozeman(unpublished MS?) tagged yellow eelsin a Georgia estuary and used recap-
ture data to estimate growth rates.There was a slow-growth period duringNovember through February when thefish grew an average of 0.025 mm perday. They grew more rapidly duringthe rest of the year, gaining anaverage of 0.220 mm per day. Theserates produced an average annuallength increase of 57 to 63 mm.
Maximum age of yellow eels col-lected from northern rivers has beenreported to be 15 to 20 years (Fahay1978). Landlocked eels liberated aselvers in Sherman Lake, Michigan,lived 35 to 40 years (Vladykov 1973).Accuracy of estimates of the age atmaturity may be affected by problemswith aging techniques.
COMMERCIAL AND SPORT FISHERIES
Prior to the 1970's, the eelfishery in the South Atlantic Bightprimarily provided live bait to sport
Table 1. Lengths of American eels at various ages.
rotal length (CIII) at various locations
Age Bi"'s Lakek~ Nek+ Newfound,andb LakeOntarioCNW
JerseydRhode
(Yr) New Erunswc IslandeDelaware SouthRiverf Carolina9
1
irI I IIV 22-38V 26-48VI 24-51VIIVIIIIXXX IXIIXIIIXIV
KIXVI IXVIIIXIX
___-__
20-26
34-5638-5738-5749-57___-_____
___
___20-2221-2725-3529-4230-5232-5534-5942-56-____________________--____
_______--____________
53-6260-6558-6958-7268-7672-8079-87
889293___
___
12,;I,,22-4722-4722-4732-5237-6237-6237-6247-6247-6747-6247-6241-7262-72a7
___ _-_
--_ ---29-32 ___ 27-46 28-5141-67 28-5136-67 29-5844-70 33-6437-74 38-6244-86 37-6563-90 46-6567-94 ---68-98 ---78-97 ---78-104 ---77-100 ---95-99 ---_-- _--_-_ __-
12-1614-25la-2824-3226-3428-4229-4335-4735-5040-5245-5443-64__-
56-59__-___-_-__-__-
20-3121-5022-5928-6232-6631-6842-7440-6944-7353-6765-6965-74
a379
bGray aSmith and and Andrews Saunders 1971. 1955.
$lurley 1972.1970.
eBieder Ogden 1971.fJohnson 1974Ildata combine; from Harrell 1977, Hansen 1979, and Michener 1980.
9
fishermen and secondarily providedbait used in blue crab (Callinectessapidus) traps. A larger commercialfishery for eels in. the reqion isdeveloping, and glass eels, elvers,yellow eels, and silver eels areexploited. Techniques for capturingand growing elvers to marketable sizesare being developed (Easley and Freund1977).
The European market has been themajor outlet of U.S. yellow and silvereel landings (Fahay 1978). Eels arehardy and can be densely packed andshipped alive if they are kept moist,cool, and supplied with oxygen. Liveeels are preferred in Europe, but manyare shipped frozen.
Commercial fishermen use avariety of methods, including liftnets, drift nets, traps, weirs, ottertrawls, pound nets, fyke nets, spears,handlines, eel pots, haul seines, andgill nets (Fahay 1978). The fyke netis the major gear used in NorthCarolina to exploit eels that aremoving seaward in late summer or earlyfall to begin their spawning migra-tion. Yellow eels in fresh- orbrackish waters are primarily takenwith baited traps or eel pots.
Fahay (1978) summarized catchstatistics along the Atlantic coastfor 1955-73. Landings from the MiddleAtlantic (New Jersey-Virginia) consis-tently exceeded those from the NorthAtlantic and South Atlantic States,but landings from Southern Statesincreased in the late 1960's and early1970's. For 1955-64, the SouthAtlantic harvest averaged about 37,000kg annually, and for 1965-73, annuallandings were about 630,000 kg. Thevalue of these landings ranged from$8,000 to $83,000 annually for 1965-73.
Eel harvest and value in NorthCarolina dramatically increased in the1960's and 1970's (Easley and Freund1977). For 1960-70, average annuallandings were 17,800 kg valued at
$O.ll/kg; in 1972-73, the price roseto $0.35/kg; and in 1973-76, landingsaveraged 151,200 kg at a price of$0.92/kg. Catch value ranged from$0.95 to $1.85/kg and harvest averaged285,000 kg for 1977-79 (Keefe 1982).The bulk of the North Carolina land-ings is taken from northeasterncoastal areas.
In Georgia, commercial fishingfor eels in freshwater was effectivelyprohibited prior to 1980 because ofrestrictions against using traps ininland waters. Harvest in 1979 wasabout 3,900 kg (Helfman, unpublishedMS4). After a freshwater trap fisherywas allowed in 1980, harvest was50,000 kg, but landings in 1981 and1982 were 5,500 kg and 16,800 kg,respectively. The 1982 catch wasvalued at $35,000 or $2.08/kg.
A fishery for European eel elversbegan in Europe during the late 1960'sto supply Japan's demand for youngeels to use in pond aquaculture.Experimental work on techniques forcapturing migrating American eelelvers has been done in the St. JohnsRiver,1973).
Florida (Topp and RaulersonElvers were packed live in
boxes and shipped to Japan, whereprices paid for local Anguillaja onica elvers were $7/kg in 1965-68,+*3OO/kg in 1969, and $330 to $925/kgin 1971-73 (Fahay 1978; Egusa 1979).Prices paid for European eel elvers inJapan initially were equivalent tothose paid for local elvers, butEuropean eels were inferior in thepond culture systems (poor growth anddisease problems); in 1973, theJapanese paid only $30 to $5O/kg forEuropean elvers (Eg usa 1979).Accounts of American eel performancein Japanese eel culture were notlocated.
'Development and expansion of thefishery for American eels in Georgia.G.S. Helfman, Department of Zoology,University of Georgia, Athens,. GA.30602. Project summary, University ofGeorgia Sea Grant Program, 1983.
10
L
The feasibility of commercialgrow-out operations in North Carolinawas assessed by Easley and Freund(1977). Interest in culturing wasstimulated by rising prices notedabove during the late 1960's and early1970's, but considerable refinement oftechniques is needed. Development ofeel aquaculture has focused on methodsfor collecting elvers and on physicalfeatures of grow-out systems. Hormoneinjections can be used to inducematuration of female American eels(Edel 1976), but proper spawning con-ditions are unknown, and eel cultureremains dependent on capturing wildelvers. Hinton and Eversole (1978,1979, 1980) evaluated the toxiceffects of chemicals commonly used inaquaculture to glass eels (mean lengthof 55 mm), elvers (mean length of 97mm), and yellow eels collected fromSouth Carolina rivers.
The South Atlantic States havefew, if any, restrictions specificallydesigned to regulate yellow or silvereel harvest, but fisheries for yelloweels often have been nonexistent orminimal because of prohibitionsagainst using traps in freshwaters (asmentioned above for Georgia). Suchrestrictions generally are intended toprevent incidental catches of sportfishes. Mouth diameter and wire meshsizes of traps are regulated in someareas to reduce catches of otherspecies1978). E~~~~~~fis~~~be~~e~ll~~al al,,
Georgia.
Estimates of density, mortality,or other vital statistics of eelstocks generally have not been report-ed, and factors regulating survival orstock size have not been evaluated.Helfman (unpublished MS?) suggestedthat the eel's long life in fresh-waters may make the stocks prone tolocal overharvest. Keefe (1982)suggested that recent declines incatch per unit effort of eels in NorthCarolina indicated overharvest.Because all American eels spawn in theSargasso Sea and there apparently are
.l
no genetically distinct stocks orsubpopulations (Koehn and Williams1978), overharvest in one region couldaffect recruitment in other regions.Nevertheless, some management policiesallow or encourage local heavy exploi-tation of migrating silver eels orelvers under the assumption that thenumbers of elvers returning in lateryears will be maintained by escapementof spawning stock from other areas.
No major sport fishery forAmerican eels exists in coastal riversof the South Atlantic Bight, but thespecies is caught incidentally byanglers in estuaries and rivers.
ECOLOGICAL ROLE
Yellow eels are nocturnal and asignificant portion of their feedingoccurs at night. The diet is diverseand generally includes nearly alltypes of aquatic fauna that occupy thesame habitats. Eels swallow sometypes of prey whole, but they also cantear pieces away from larger deadfish, crabs, or other items. Eels infreshwater feed on insects, worms,crayfish and other crustaceans, frogs,and fish whereas elvers in saltwaterare planktivorous. Elvers collectedfrom the Cooper River, South Carolina,consumed aquatic insects (mainlychironomid larvae and adults), clado-cerans, amphipods,(McCord 1977).
and fish partsThe diet of yellow
eels from the Cooper River varied witheel size and season. Intermediatesize classes contained more types offood than elvers or maturing eels;fish occurred in the diet primarily inwinter and spring whereas insects andmollusks were eaten from springthrough fall. Crustaceans, bivalves,and polychaetes were the major prey ofeels in lower Chesapeake Bay; bluecrabs and soft clams were significantprey (Wenner and Musick 1975). Eelsshorter than 40 cm in New Jerseystreams mainly ate aquatic insectswhereas larger eels fed mostly on fishand crustaceans (Ogden 1970). Most
.
fish eaten were bottom dwellers,reflecting the eels' tendency toremain near the bottom. Fahay (1978)concluded that eels depend more onscent than sight to obtain food.
Little has been published about..predation on eels. tiornberger et al.(1978) reported that elvers and smallyellow eels were eaten by largemouthbass (Micro terussalmoides) a n dstriped bass Morone sm in the
1
Cooper River, South Carolina, but eelsnever were a major component of thesepredators' diets. Leptocephali, glasseels, elvers, and small yellow eelsprobably are consumed by a variety ofother predatory fishes; grown eels areeaten by other species of eels and bygulls, bald eagles, and other fish-eating birds (Sinha and Jones 1967 ;Seymour 1974).
Crane and Eversole (1980) foundno parasites on glass eels migratinginto the Cooper River, South Carolina,but four genera of protozoans (Tricho-~i~~~o~~~,"h~p,"","~,ri~~ec~:idoif"mAo~~d
genetic trematode (Gyrodactylusanguillae) were found on elvers.Crane and Eversole (in press) reportedthat 214 of 218 yellow eels collectedfrom brackish waters of the CooperRiver, South Carolina, were parasit-ized by one or more of 22 helminthspecies. Parasites of American eelsin Quebec included protozoans, trema-todes, nematodes, cestodes, andcopepods (Hanek and Molnar 1974). Themyxosporidian protozoan, Myxidiumzelandicum, has been found in thekidneys and on the gills of A.rostrata (Komourdjian et al. 1977).
ENVIRONMENTAL REQUIREMENTS
Temperature
The eel's broad geographic rangeand diverse habitats suggest flexibletemperature requirements. Elvers andyellow eels live in waters rangingfrom cold, high-elevation or high-
latitude freshwater streams and lakesto warm, brackish coastal bays andestuaries in the Gulf of Mexico.Jeffries (1960) found elvers attemperatures as low as -0.8" C.
Barila and Stauffer (1980)acclimated yellow eels to a range oftemperatures between 6' C and 30" Cand then measured preferred tempera-tures. Although preferred tempera-tures tended to increase withincreased acclimation temperature,differences among groups were nonsig-nificant, and the authors reported afinal temperature preference of 16.7'C. They also reported that feedingceased at temperatures below 14' C.Marcy (1973) reported that Americaneels survived passage through thecooling system of a nuclear powerplant, during which they were exposedto elevated temperatures for l-l.5 hr.Poluhowich (1972) suggested that theAmerican eel's multiple types of hemo-globins serve to maintain a relativelyconstant blood oxygen affinity whenthe eel is exposed to temperaturechanges.
Salinity
The mechanisms by which glasseels or elvers orient during %heirshoreward migration have not beendescribed, but their movementsprobably are keyed to salinitygradients after they reach coastalwaters. European glass eels andelvers become positively rheotacticwhen they first encounter freshwaterthat is mixed with seawater (Tesch1977); thus salinity as well as thecurrent itself may provide the gradi-ent for shoreward orientation.Alterations of patterns or magnitudesof freshwater inflows to bays orestuaries could alter salinity regimesand thereby affect the number, timing,and spatial patterns of upstreammigrations by elvers.
As with temperature, salinityrequirements of postlarval eels can begenerally inferred as "broad" from the
12
L
k
fact that the species occurs through-out a gradient of strictly fresh tobrackish waters. Leptocephali are innear-ionic equilibrium with sea water(Hulet et al. 1972).
Dissolved Oxygen
Dissolved oxygen requirementshave not been thoroughly documented,but eels generally will select waterwith high oxygen tension (Hill 1969).Commercial shipping of live eelsindicates that they are especiallyhardy. Elvers can be packed denselyand shipped alive by being dampenedbut not covered with water becausethey can absorb 60% of required oxygenthrough their skin (Sheldon 1974,cited by Fahay 1978). Tesch (1977)stated:
"The capacity of the adult eelto survive in both air and wateris associated with its ability touse both branchial and cutaneousmodes of respiratory gas ex-change. The eel survives betterin air than in poorly oxygenatedor polluted water . ...'
Habitat Structure
Postlarval eels tend to be bottomdwellers and hide in burrows, tubes,snags, plant masses, other types ofshelter, or the substrate itself(Fahay 1978). This behavior isreflected in their food habits, pro-tects them from predators, and influ-ences commercial fishing techniques.Few other freshwater fishes displaysimilar habitat use; therefore, inter-specific competition for living spacemay be limited. The presence of soft,undisturbed bottom sediments is impor-tant to migrating elvers as shelter(see the Elver Stage section). Edel(1979) indicated that eels in hisexperimental systems were less activewhen shelter was present than when itwas absent. Vladykov (1955, cited byFahay 1978) reported that adult eelsin northern habitats lie dormant inthe bottom mud during winter.
Ford and Mercer (1979) used mark-recapture methods to obtain a popula-tion estimate of 350 yellow eels in a600-m section of a marsh creek in aMassachusetts estuary. They studiedthe behavior of yellow eels and foundthat eels shorter than 30 cm predomi-nated in narrow, soft-bottomed, uppermarsh creeks whereas those longer than30 cm predominated in wider, lowermarsh creeks having mud and sandbottoms. Most eels had relativelysmall home ranges and rarely movedmore than 100 m from the point atwhich they were initially caught.The authors believed that large eelsmay establish territories in lowermarsh areas and thereby restrictsmaller eels to smaller high marshcreeks.
River and Tidal Currents
The elver's nocturnal activitypatterns and reliance on tides andriver currents for upstream movementare presented in the LIFE HISTORYsection.
Movements of yellow eels in atidal creek in Georgia were affectedby tides and time of day (Helfman etal. 1983). Daytime movements of eighttelemetered eels were restricted tothe main creek channel, but at nightthe fish were near the mouths offeeder creeks at low tide or inflooded marsh areas during high tide.Helfman et al. (1983) termed thismovement 'a nocturnal activity patternmodified by tidal flow." They sug-gested that movements onto the marshat night may have been foraging trips.
Contaminants
Little work has been done onAmerican eels regarding toxic effectsof pollutants or tolerance limits.Tolerance would be expected to varywith developmental phase, and theeel's long residence in freshwaterrivers could lead to repeated doses oftoxicants and accumulation to toxiclevels (Holmberg and Saunders 1979).
3
Work done bv Hinton and Eversole(1978, 1979,- 1980) on toxicity ofaquaculture chemicals to various lifestages of eels suggests that toleranceto chemicals increases with size orage.
Environmental Factors and SexDetermination
There is limited evidence whichsuggests that the gender of Americaneels is determined to some extent byenvironmental factors. Fahay (1978)stated that the sex of the Europeaneel can be environmentally influenced,but indicated that the factors respon-sible could only be speculated upon.The long developmental period infresh- or brackish waters in combina-tion with juvenile hermaphroditism(see the LIFE HISTORY section) pro-vides a setting in which environmentalfactors could regulate the gender ofeels.
Female American eels predominatein upstream freshwater areas as wellas in northerly stocks, but there isno direct evidence of mechanisms thatlead to these patterns. One possibleexplanation is that male leptocephaliand elvers do not migrate as far asfemales (and hence remain in southerlyor downstream areas [Fahay 19781).But because eels do not mature untilthey have lived 3 yr (males) to 7 yr(females) or longer in freshwater, itis unlikely that physiological systemscapable of causing sex-related differ-ences in migratory patterns would. be
.4
developed in the youngest life stages.It is possible that male eels preferhigher salinities than females andmove downstream to coastal areas afterthey are differentiated, but thisbehavioral pattern has not beenobserved and it would not explain thelatitudinal trend.
Koehn and Williams (1978) report-ed that eels throughout the species'range are part of the same spawningstock. They concluded that differ-ences in protein characteristics inyellow eels from different drainagesalong the Atlantic coast reflectedenvironmental differences. Thissuggests that latitudinal variationsin the sex ratio are not geneticallydetermined but could be due to varia-tions of environmental factors. Someof the environmental factors thatcould be involved include food qualityand population densit
y(Fahay 1978).
Parsons et al. (1977 believed thatstocking of European eel elvers intoLough Neagh, Northern Ireland, led toa higher population density and amarked increase in the proportion ofmale eels that subsequently emigratedfrom the lake. Similarly, Egusa(1979) indicated that A. anguillaelvers grown in Japanese-ponds undercrowded conditions produced malespredominantly, suggesting that varia-tions in the sex ratio of American eelpopulations may be related to popula-tion density. Salinity apparently isnot an important sex determinant; sexratios were similar in the freshwaterand brackish culture ponds studied byEgusa.
LITERATURE CITED
‘L
Barila, F. Y., and J. R. Stauffer, Jr.1980. Temperature behavioralresponses of the American eel.Anguilla rostrata (LeSueur), fromMaryland. Hydrobiologia 74:49-51.
Beatty, D. 0. 1975. Visual pigmentsof the American eel, Anguillarostrata. Vision Res. 15:771-776.
Bertin, L. 1956. Eels: a biologicalstudy. Cleaver-Hume Press Ltd.,London. 197 pp.
Bieder, R. C. 1971. Age and growthof the American eel, Anguillarostrata (LeSueur), in RhodeIsland. M.S. Thesis. Universityof Rhode Island, Kingston, R.I.39 PP.
Bigelow, H. B., and W. C. Schroeder.1953. Fishes of the Gulf ofMaine. U.S. Fish Wildl. Serv.Fish. Bul. 53. 577 pp.
Crane, J. S., and A. G. Eversole.1980. Ectoparasitic fauna ofglass eel a'nd elver stages ofAnerican eel (Anguilla rostrata).Proc. World. Maricult. sot.11: 275-280.
Crane, J. S., and A. G. Eversole. Inpress. Helminth parasites ofAmerican eels from brackishwater. Proc. Annu. Conf. South-east. Assoc. Fish Wildl. Agen.35:357-366.
Deelder, C. L. 1958. On the behaviorof elvers (Anguilla vulgarisTurt.) migrating from the sea
into fresh water. J. Conserv.24:135-146.
Dolan, J. A., and G. Power. 1977. Sexratio of American eels, Anguillarostrata, from the Matamek Riversystem, Quebec, with remarks onproblems in sexual identifica-tion. J. Fish. Res. Board Can.34:294-299.
Eales, J. G. 1968. The eel fisheriesof eastern Canada. Bull. Fish.Res. Board Can.166. 79 pp.
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Egusa, S. 1979. Notes on the cultureof the European eel (An uillaanguilla L.) in Japanese%zfarming ponds. Rapp. P.-V. Reun.Cons. Int. Explor. Mer 174:51-58.
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Eldred, B. 1971. First records ofAnguilla rostrata larvae in theGulf of Mexico and YucatanStraits. Fla. Dep. Nat. Resour.,Mar. Res. Lab. Leafl. Ser. 4:1-3.
Facey, D. E., and G. W. LaBar. 1981.Biology of American eels in LakeChamplain, Vermont. Trans. Am.Fish. Sot. 110:396-402.
Fahay, M. P. 1978. Biological andfisheries data on American eel,Anguilla rostrata (LeSueur). U.S. Dep. Commer. Natl. Mar. Fish.Serv. Tech. Ser. Rep. No. 17,Northeast Fisheries Center,Highlands, N.J. 82 pp.
Ford, T., and E. Mercer. 1979. Popu-lation density, size distribu-tion. and home ranoe of theAmerican eel (Anguilla rostrata)in the Great Sippewissett saltmarsh. (Summary only.) Biol.Bull. 157:368.
Gray, R. W., and C. W. Andrews. 1971.Age and growth of the Americaneel (Anguilla rostrata (LeSueur))in Newfoundland waters. Can. J.Zool. 49:121-128.
Hanek, G., and K. Molnar. 1974. Para-sites of freshwater and anadro-mous fishes from Matamek Riversystem, Quebec. J. Fish. Res.Board Can. 31:1135-1139.
Hansen, R. A. 1979. Age, growth, andsex ratio of the American eel.Anguilla rostrata (LeSueur), inbrackish water portions of CooperRiver, South Carolina. M.S.Thesis. Clemson University,Clemson, S.C. 45 PP.
Hansen, R. A., and A. G. Eversole.In press. Age, growth, and sexratio of the American eel inbrackish water portions of theCooper River, South Carolina.Trans. Pm. Fish. Sot.
Harrell, R. M. 1977. Age, growth,and sex ratio of the Americaneel, Anguilla rostrata (LeSueur),
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University, Clemson, S.C. 55 pp.
Harrell, R. M., and H. A. Loyacano,Jr. 1980. Age, growth and sexratio of the American eel in theCooper River, South Carolina.Proc. Annu. Conf. Southeast.Assoc. Fish. Wildl. Agen. 34:349-359.
Helfman, G. S., D. L. Stoneburner, E.L. Bozeman, P. A. Christian, andR. Whalen. 1983. Ultrasonictelemetry of American eel move-ments in a tidal creek. Trans.Am. Fish. Sot. 112:105-110.
Hill, L. J. 1969. Reactions of theAmerican eel to dissolved oxygentensions. Tex. J. Sci. 20:305-313.
Hinton, M. J., and A. G. Eversole.1978. Toxicity of ten commonlyused chemicals to American eels.Proc. Annu. Conf. Southeast.Assoc. Fish. Wildl. Agen. 32:599-604.
Hinton, M. J., and A. G. Eversole.1979. Toxicity of ten chemicalscommonly used in aquaculture tothe black eel stage of theAmerican eel. Proc. WorldMaricult. Sot. 10:554-560.
Hinton, M. J., and A. G. Eversole.1980. Toxicity and tolerancestudies with yellow-phase eels.Prog. Fish-Cult. 42:201-203.
Holmberg, B., and R. L. Saunders.1979. The effects of penta-chlorophenol on swimming perfor-mance and oxygen consumption inthe American eel (Anauillarostrata). Rapp. P.-V. Reun.Cons. Int. Explor. Mer 174:144-149.
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Hornberger, M. L. 1978. CoastalPlains American eel study. Pages42-50 in Progress report forOctober- 1977 through January1978. S.C. Wildl. Mar. Res.Dep., Charleston.
Hornberger, M. L., J. S. Tuten, A.Eversole, J. Crane, R. Hansen,and M. Hinton. 1978. Americaneel investigations. Completionreport for March 1977-Julv 1978.S.C. Wildl. MarCharleston, andClemson. 311 pp.
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Hulet, W. H., J. F scher, and B.Rietberg. 1972 . Electrolytecomposition of anguilliformleptocephali from the Straits ofFlorida. Bull. Mar. Sci.22:432-448.
Hurley, D. A. 1972. The American eel(Anguilla rostrata) in easternLake Ontario. J. Fish. Res.Board Can. 29: 535-543.
Jeffries, H. P. 1960. Winter occur-rences of Anguilla rostrataelvers in New England and MiddleAtlantic estuaries. Limnol.Oceanogr. 5~338-340.
Johnson, J. S. 1974. Sex distribu-tion and age studies of Anguillarostrata (American eel) in freshwaters of the Delaware River.M.S. Thesis. East StroudsburgState College, East Stroudsburg,Pa. 57 PP.
Keefe. S. G. 1982. The American eel(Anguilla rostrata) fishery inthe commercial waters of NorthCarolina. Paoes 50-51 in K. H.Loftus, ed. Proceedingsof the1980 North American eel confer-ence. Ontario Fish. Tech. Rep.Ser. No. 4, Ontario Ministry ofNat. Resour., Toronto. 97 pp.
Kleckner, R. C., and W. H. Kruger.1981. Changes in swim bladderretial morphology in Anguilla
rostrata during premigrationmetamorphosis. J. Fish Biol.18:569-577.
Koehn, R. K., and G. C. Williams.1978. Genetic differentiationwithout isolation in the Americaneel , Anguilla rostrata. II.Temporal stability of geographicpatterns. Evolution 32:624-637.
Komourdjian, M. P., W. C. Hulbert, J.C. Fenwick, and T. W. Moon. 1977.Descriotion and first occurrenceof Myxidium zealandicum (Proto-zoa: Myxosporidia) in the NorthAmerican eel Anguilla rostrataLeSueur. Can. J. Zool. 55:52-59.
Marcy, B. C., Jr. 1973. Vulnerabilityand survival of young ConnecticutRiver fish entrained at a nuclearpower plant. J. Fish. Res. BoardCan. 30:1195-1203.
McCord, J. W. 1977. Food habits andelver migration of Americaneel, Anguilla rostrata,(LeSueur). in Cooper River,South Carolina. M:S. Thesis:Clemson University, Clemson,S.C. 47 PP.
Michener, W. K. 1980. Age, growth,and sex ratio of the Americaneel, Anguilla rostrata (LeSueur),from Charleston Harbor, SouthCarolina. M.S. Thesis. ClemsonUniversity, Clemson, S.C. 49 pp.
Miles, S. G. 1968. Laboratory experi-ments on the orientation of theadult Americanrostrata.
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Ogden, J. C. 1970. Relative abun-dance, food habits, and age ofthe American eel, Anguillarostrata (LeSueur), in certainNew Jersey streams. Trans. Am.Fish. Sot. 99:54-59.
Pacheco, A. L., and G. C. Grant. 1973.Immature fishes associated with
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larval Atlantic menhaden atIndian River Inlet, Delaware,1958-61. Pages 78-117 in A. L.Pacheco, ed. Proceedings of aworkshop on egg, larval, andjuvenile stages of fish inAtlantic coast estuaries. MiddleAtlantic Coastal Fisheries CenterTech. Publ. No. 1.
Parsons, J., K. U. Vickers, and Y.Warden. 1977. Relationshipbetween elver recruitment andchanaes in the sex ratio ofsilver eels Anguilla anguilla L.migrating from Lough Neagh,Northern Ireland. J. Fish. Biol.lO:Zll-229.
Poluhowich, J. J. 1972.significance of eelhemoglobins. Physio45:215-222.
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Stasko, A. B., and S. A. Rommel, Jr.1977. Ultrasonic tracking ofAtlantic salmon and eels. Rapp.P.-V. Reun. Cons. Int. Explor.Mer 179:36-40.
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Topp, R., and R. Raulerson. 1973.Elver investigations in thesoutheast. U.S. Natl. Mar. Fish.Serv. Mar. Fish. Rev. 35:45-47.
18
Vladykov, V. D. 1955. Eel fishes ofQuebec. Quebec Dep. of Fish.Album No. 6:1-12.
Vladykov, V. D. 1964. Quest for thetrue breedino area of the Ameri-can eel -(Anguilla rostrataLeSueur). J. Fish. Res. BoardCan. 21:1523-1530.
Vladykov, V. D. 1966. Remarks on theAmerican eel (Anguilla rostrataLeSueur). Sizes of elversentering streams; the relativeabundance of adult males andfemales; and present economicimportance of eels in NorthAmerica. Verh. Int. Verein.Theor. Angew. Limnol.16:1007-1017.
Vladykov, V. D. 1973. Macrophthalmiain the American eel (Anauillarostrata). J. Fish. ResmCan. 30:689-693.
Vladykov, V. D., and H. March. 1975.Distribution of leptochephali ofthe two species of Anguilla inthe western North Atlantic basedon collections made between 1933and 1968. Syllogeus 6:1-38.
Wenner, C. A. 1973. Occurrence ofAmerican eels, Anguilla rostrata,in water overlyinq the easternNorth American ConGnental Shelf.J. Fish. Res. Board Can.30:1752-1755.
Wenner, C. A., and J. A. Musick. 1974.Fecundity and gonad observationof the American eel. Anauillarostrata, migrating from Chesa-peake Bay, Virsinia. J. Fish.Res. Board Can.-31:1387-1391.
Wenner, C. A., and J. A. Musick. 1975.Food habits and seasonal abun-dance of the American eel,Anguilla rostrata, from the lowerChesapeake Bay. Chesapeake Sci.16:62-66.
19
SO272 -161
REPORT DOCUMENTATION .L’=mRT NO. 2. 3. Recioienf’f Accession No.
PAGE FwS/OBS-82/11.24*4 . ntk and Subtltlo Species Profi 1 es : Life Histories and Environmental s.~*wfloat*
Requirements of Coastal Fishes and Invertebrates (South Atlan- July 1984tic)--American eel 6.
7. Author(s)Michael J. Van Den Avyle
0. Performin Orlanlxatian N.m. and AddrmssGeorgia Cooperative Fishery Research UnitSchool of Forest ResourcesUniversity of GeorgiaAthens, GA 30602
6. Performme Oreanirrcion RePi. NO .
10. Proi*ct/Task/Wwk Unit NO.
11. Contnc~fQ or Cranr(t) NO.
(C)(G)
12 fpmsotine Or6mirwtlon ram* an* Address 13. Tyw of Rewn 6 P e r i o d Covered
National Coastal Ecosystems Team U.S. Army Corps of EngineersFish and Wildlife Service Waterways Experiment StationU.S. Department of the Interior P.O. Box 631 14.
Washington, DC 20240 Vicksburg, MS 3918015. Suppl*mantwy Notes
*U.S. Army Corps of Engineers report No. TR EL-82-4
‘16. Abstract (Limir 200 words)
Species profiles are literature summaries of taxonomy, life history, and environmentalrequirements of coastal fishes and aquatic invertebrates. They are prepared to assistwith impact assessment. The American eel, Anguilla rostrata, is an ecologically andeconomically important catadromous species that occupies freshwater streams, rivers,brackish estuaries, and the open ocean during various phases of its life cycle. Adulteels apparently spawn in the Sargasso Sea, and ocean currents transport the developinglarvae northward until the young metamorphose into juveniles capable of swimmingshoreward and moving upstream into coastal areas, estuaries, and rivers. Developingeels commonly remain in freshwater or brackish areas for lo-12 years before migratingto spawn. American eels tend to be bottom-dwellers and feed on a variety of faunathat occupy the same habitats. Eels occupy areas having wide ranges of temperature,salinity, and other environmental factors, suggesting broad tolerance limits, but fewstudies of requirements have been reported. Salinity patterns and water currentscreated by river discharges into coastal areas apparently provide the gradient thatcues shoreward migration of juvenile eels. Alteration of patterns of freshwaterinflows to estuaries and bays could affect upstream migrations.
17. Doeummt Analy%is 4. D*awifuorsEelDistributionMigrationFeedinaRivers-
b. Id~ntifi~n/OPmXnd,d TwmsAnguilla rostrataCatadromousLife historyEnvironmental requirements
c. COSATI FiddlGtoup
16. AvaIlabilIty StMm%.nt
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Headquarters. Division of BiologicalServices, Washington, DC
Eastern Energy and Land Use TeamLeetown, WV
Natmnal Coastal Ecosystems TeamSlidell, LA
Western Energy and Land Use TeamFt. Collins, CO
l Locations of Regional Offices
REGION 1Regional DirectorU.S. Fish and Wildlife ServiceLloyd Five Hundred Building, Suite 1692500 N.E. Multnomah StreetPortland, Oregon 97232
REGION 4Regional DirectorU.S. Fish and Wildlife ServiceRichard B. Russell Building75 Spring Street, S.W.Atlanta, Georgia 30303
Kesearch LibraryU.S. Department of the InteriorNational Biological ServiceSouthern Science Center700 Cajundome Blvd.Lafayette, LA 70.506-3 152
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REGION 2 REGION 3Regional Director Regional DirectorU.S. Fish and Wildlife Service U.S. Fish and Wildlife ServiceP.O. Box 1306 Federal Building, Fort SnellingAlbuquerque, New Mexico 87 103 Twin Cities, Minnesota 55 I 11
REGION 5Regional DirectorU.S. Fish and Wildlife ServiceOne Gateway CenterNewton Corner, Massachusetts 02158
REGION 6Regional DirectorU.S. Fish and Wildlife ServiceP.O. Box 25486Denver Federal CenterDenver. Colorado 80225
REGION 7Regional DirectorU.S. Fish and Wildlife Service1011 E. Tudor RoadAnchorage, Alaska 99503
DEPARTMENT Of THE INTERIORU.S. FISH AND WILDLIFE SERVICE
As the Nation’s principal conservation agency, the Department of the Interior has respon-sibility for most of our nationally owned public lands and natural resources. This includesfostering the wisest use of our land and water resources, protecting our fish and wildlife,preserving theenvironmental and cultural values of our national parks and historical places,and providing for the enjoyment of life through outdoor recreation. The Department a!$-sesses our energy and mineral resources and works to assure that their development is inthe best interests of all our people. The Department also has a major responsibility forAmerican Indian reservation communities and for people who live in island territories underU.S. administration.
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