The American eel, Anguilla rostrata, is a catadromous fish found on the eastern coast of North America. The American eel has a slender snakelike body that is covered with a mucous layer, which makes the eel appear to be naked and slimy despite the presence of minute scales. A long and dorsal fin runs from the middle of the back and is continuous with a similar ventral fin. Pelvic fins are absent, and relatively small pectoral fin can be found near the midline, followed the head and gill-covers. Variations exist in coloration, from olive green, brown shading to greenish-yellow and light gray or white on the belly. Eels from clear water are lighter than those from dark, tannic acid streams [1]
The eel lives in fresh water and only leaves this habitat to enter the Atlantic ocean for spawning. It takes 9 to 10 weeks for the eggs to hatch. After hatching, young eels move toward North America and enter freshwater systems to mature. The female can lay up to 4 million buoyant eggs a year, but dies after egg-laying.
The eel is found around the Atlantic coast including Chesapeake Bay and the Hudson River. It prefers to hunt at night, and during the day it hides in mud, sand or gravel very close to shore, roughly 5 to 6 feet under.
American eels are economically very important to the East Coast and rivers where they travel. They are caught by fishermen and sold, eaten, or kept as pets. Eels help the Atlantic coast ecosystem by eating dead fish, invertebrates, carrion, insects, and if hungry enough, they will cannibalize each other.
Eels were once an abundant species in rivers, and were an important fishery for aborignal people. The construction of power dams, however, has blocked migration and locally exterminated eels in many watersheds. For example, in Canada, the vast populations of eels in the St. Lawrence and Ottawa Rivers have dwindled[2].
Although many anglers are put off by the snake-like appearance of these catadromous fish, eels are in fact fit for human consumption. They are usually caught by anglers seeking other catch. The world record weight for the American eel is 9.25 pounds.
The American Eel Anguilla rostrata was first described in 1817 by Lesueur. Anguilla is Latin for eel, and rostrata is a Latin words that can mean either "breaked or curved" or "long nose" French: Anguille d’Amèrique Spanish: Anguila americana.
The body of Anguilla rostrata is elongate with compressed behind and snake-like. Its dorsal and anal fins confluent with the rudimentary caudal fin. It lacks ventral fins but pectoral fins are present. Lateral line well-developed and complete. The head is long and conical with rather small well developed eyes. Mouth is terminal with not jaws that are not particularly elongated. Their teeth are small, pectinate or setiform in several series on the jaws and the vomer. Minute teeth also present on the pharyngeal[disambiguation needed 
] bones, forming a patch on the upper pharyngeals. Tongue present with thick lips that are attached by a frenum in front. Nostril are superior and well separated. The body is covered with minute embedded linear scales that are placed obliquely, some at right angles to others. Gill openings are partly below pectoral fins, relatively well-developed and well separated from one another. Inner gill slits are wide. [3] [4] [5]
Females are generally larger than males, lighter in color, smaller eyes and higher fins. [6]
American eels can grow to 1.22m in length and to 7.5kg in weight. Females grow much larger in size comparing to males.
Adult eels as well as eels at various developmental stages are commonly found in freshwater, coastal waters, and the open ocean from the southern tip of Greenland, Labrador and Newfoundland southward along the Atlantic coast of North America, into the Gulf of Mexico and to the northern portion of the east coast of South American (Tesch 1977) [7]. Large number of this species can be found in the North Atlantic states, the eastern Canadian provinces, and southward to Mexico. It is a resident of the Mississippi Valley. The latitudinal range was reported as 5 to 62 N (Bertin 1965). [8]
Nonindigenous orccurences of this species in the United States were recorded from Lake Mead on the Colorado River and on the Arizona border (Minckley 1973)[9]. It was stocked on a few occasions in Sacramento and San Francisco bay, CA in the late 1800s. No apparent evidence of survival on these occasions was noted (Smith 1896; Shebley 1917; Shapovalov et al. 1981; McCosker 1989)[10]. It was also stocked and unintentionally introduced in various states, including Illinois (Milner 1874b; Goode 1884), Indiana (Gerking 1945)[11], Nebraska, Nevada (Minckley 1973)[9], North Carolina (Shute and Etnier 2000)[12], Ohio and Pennsylvania (Scott and Crossman 1973; Busch et al. 1977; Trautman 1980)[13], Wisconsin (Milner 1874b; Goode 1884). Stocking of this species also occurred in Utah in the late 1800s, but soon disappeared (Popov and Low 1953; Sigler and Miller 1963). [14] [15]
The American eel spawns in oceanic waters but can be found in warm brackish and freshwater streams and estuarine systems during most of its developmental stages. The species also occurs sometimes in cold freshwater trout streams in mountainous area [16]
The distribution of this species is wide, as revealed by the various range of occupied habitats, including polluted area. Temperature requirements, subsequently, are suggested to be flexible. It has been found that American eels during elver stage can survive temperature as low as -0.8oC (Jefferies 1960) [17]. Barila and Stauffer (1980) [18] reported a final mean temperature preference at 16.7oC. Karlsson et al (1984) disagreed with this interpretation and found the final temperature preference of 17.4 ± 2.0oC with a 95% confidence interval. [19]
It is also due to the species’ ease with which it can be transplanted, the ability to travel on damp ground and wet vertical surfaces, i.e. dams. Adult eels are sporadically found in landlocked lakes in the northeastern United States.
Habitat structure wise, post-larval eels tend to be bottom dwellers, hiding in burrows, tubes, snags, masses of plants, other types of shelter and the substrate [20]
The American eel is a catadromous fish that has a complex life cycle, involving in various stages of metamorphosis. Understanding of the life cycle and spawning grounds of Anguilla rostrata was severely lacking until Johannes Schmidt, a Danish ichthyologish, published his fifteen-year extensive study on the Atlantic Ocean, from Greenland to Puerto Rico and the English Channel to Chesapeake Bay. He discovered that the spawning grounds are located in the Sargasso Sea. It is an oceanic area filled with floating rafts of sargassum weed near the center of the North Atlantic gyre. Being catadromous, the American eel spends most of its life in rivers and other freshwater habitat but returns to the sea to spawn. The age of maturity has not been clearly defined. Studies suggest that maturation occurs after age III for males and age IV-VII for females for northern populations [21]
The life cycle of Anguilla rostrata includes the following 6 different stages [22]
1. Silver eels:
This is sexually mature form of American eels. Metamorphosis during this stage is critical for the eels to change physically, allowing them to return to the ocean. During this stafe, the eel is transformed from a freshwater dweller to an oceanic traveler. This process includes the changing in color from olive to almost black with silver sides (hence the name), increasing of eyes size to enhance vision in deeper water, reservation of fat for the long migration, and cessation of feeding with digestive systems degenerated. Spawning seems to occur as early as February and continue till at least April (Kleckner et al. 1983; McCleave et al. 1986).
2. Eggs: Fecundity for many eels is between about 0.5 to 4.0 million eggs, with larger individuals releasing as many as 8.5 million eggs (Wenner and Musick 1974). The diameter of egg is about 1.1mm. Fertilization is external, and adult eels are presumed to die after spawning. None has been reported to migrate up rivers.
3. Leptocephali:
This is a larval stage that is strikingly different from the adult stage that the eels will grow into. The larva eels are transparent with a small pointed head and large teeth. Larva spent 7-12 months drifting on the Gulf Stream towards their adult freshwater habitats.
The life cycle with 6 different stages of American eels
4. Glass eel: This is the stage in which the larva begins to take on a more typical eel body shape. Glass eels have laterally compressed transparent bodies, with large black eyes and pink gills. Development of the digestive system is accelerated, as well as changes in configuration of head and jaws (Fahay 1978). The eels are now morphologically similar to elvers and yellow eels but lack the pigmentations
5. Elvers: After entering into an estuarine environment, the eels as young elvers developed a gray to greenish-brown pigmentation. Some elvers remain in the marshes or along the open coast; other migrate into freshwater. At this stage, American eels are nocturnal, burrowing during the day (Deelder 1958).
6. Yellow eels: This is the sexually immature adult stage of American eel. They begin to develop a yellow color and a creamy or yellowish belly. In this phase, the eels are still mainly nocturnal. Those remained in estuarine environment continue to go through their life cycle more quickly than those traveled into freshwater. Those in freshwater, however, tend to live longer and attain much larger sizes.
Reproduction takes place in the ocean, the Sargasso Sea in particular.[23] American eels live their lives in rivers for 10 to 20 years before making the 2 to 3 month journey to the ocean. [24] Breeding generally starts in the winter but can last until summer. [25] After reproduction has been completed, the eels die. [26] Estimates range on the number of eggs produced by a female but they range from 4 million eggs [27] to 10-20 million eggs.[28]
American eels are noctural and most of their feeding is at night (Helfman 1986). Having a keen sense of olfactory, the eels most likely depend on scent to find food Fahay 1986. Their diet are diverse at a wide range for different life stages and in different habitats and on every level of the food chain. Generally, their diet includes most of the aquatic fauna sharing the same environment. Having relatively weak jaws, the eels either swallow the prey whole or spin their bodies to break apart food. It has been documented of the eels' ability to grasp large food items, i.e. large dead fish, crabs, etc., and spin rapidly to break the food into pieces. [29] Spinning frequency can go up to 6 to 14 spins per second.
The species varying diet may include small fish, aquatic insects, worms, frogs, mollusks, crustaceans, bivalves, and polychaetes. [30] [31]
Little information about predation on eels has been published. It was reported than elvers and small yellow eels are prey to largemouth bass and striped bass, although they were not a major parts of these predators' diet[32]. Leptocephali, glass eels, elvers, and small yellow eels are likely to be eaten by various predatory fishes. Older eels are also known to eat incoming glass eels[33]. They also fall prey to other species of eels, bald eagles, gulls, as well as other fish-eating birds [34]
Global capture of American eel in tonnes reported by the FAO, 1950–2009[35]
The major outlet for U.S landings of yellow and silver eels is the EU market [36]
In the 1970s, the annual North Atlantic harvest averaged 125,418kg, with an average value of $84,000. In 1977, the eel landings fro Maine, New Hampshire, and Massachusetts were about 79,700, 2,700, and 143,300kg, valued at $263,000, $5,000, and $170,000, respectively (US Department of Commerce 1984)
During the 1980s and early 1990s, the American eel was one of the top three species in commercial value to Ontario's fishing industry. At its peak, the eel harvest was valued at $600,000 and, in some years, eel accounted for almost half of the value of the entire commercial fish harvest from Lake Ontario. the commercial catch of eel has declined from approximately 223,000 kilograms (kg) in the early 1980s to 11,000 kg in 2002.[37]
Substantial decline in numbers and fishery landings of American eels over their range in eastern Canada and the US was noted, raising concerns over the status of this . The number of juvenile eels in the Lake Ontario area decreased from 935,000 in 1985 to about 8000 in 1993 and was approaching zero levels in 2001. Rapid declines were also recorded in Virginia, as well as in New Brunswick and Prince Edward Island in Canada.
Because of its complex life cycle, the species face a broad range of threats, some of which are specific to certain growth stage. Being catadromous, the eels's reproductivity success depends heavily on free downstream passage for spawning migration. It also depends on the availability of diverse habitats for growth and maturation.
Sex ratio in the population can also be affected because males and females tend to utilize different habitats. Impacts on certain regions may greatly impact the number of either sex.
Despite being able to live in a wide range of temperatures and different levels of salinity, American eels are very sensitive to low dissolved oxygen level [38], which is typically found below dams. Contaminations of heavy metals, dioxin[disambiguation needed ], chlordane, and polychlorinated biphenyls as well as pollutants from nonpoint source can bioaccumulate within the fat tissues of the eels, causing dangerous toxicity and reduced productivity [39]. This problem is exacerbated due to the high fat content of eels.
Construction of dams and other irrigation facilities seriously decreases habitat availability and diversity for the eels. Dredging can affect migration, population distribution and prey availability. Overfishing or excessive harvesting of juveniles can also negatively impact local populations.
Other natural threats come from interspecific competition with [[exotic species] like the flathead catfish (Pylodictis olivaris) and blue catfish (Ictalurus furcatus), pathogens and parasites, and changes in oceanographic conditions that can alter currents-this potentially alter larval transport and migration of juveniles back to freshwater streams.
Management of the species had been virtually non-existent till very recently. Information on the species is still limited and much more efforts are needed for a longterm plan to monitor localized populations.
- The Canadian province of Ontario has cancelled the commercial fishing quota since 2004. Eel sport fishery has been closed. Efforts have been made to improve the passage in which eels migrate across the hydroelectric dams on St. Lawrence River [40]
Some recommendations from the Department of Natural Resources of South Carolina:
- Determine size, sex, and age structures for each sub-population of American eels.
- Determine potential presence and distribution of the Asian swimbladder nematode (Anguillicola crassus).
- Determine potential impacts to American eels from competition and predation by non-native species.
- Determine the scope and impact of American eel harvest on sub-populations.
- Conduct genetics studies to document sub-populations by region or river basin.
- Investigate opportunities to provide passage at dams and other obstructions that are not under FERC authority.
- Develop more cost-effective and efficient techniques for providing both upstream and
- downstream passage of American eels at migration barriers.
- Where possible, improve access to a full diversity of habitats by removing, breeching or bypassing impediments to migration such as nonfunctional dams, dikes or causeways.
- Partner with NMFS, USFWS, United States Army Corps of Engineers and non-governmental organizations (NGOs) to promote the inclusion of fish passage designs,wherever prescribed, that can successfully provide two-way passage of American eel.
- Build partnerships with NGOs, permitting authorities and county and local governments to improve and implement the use of Best Management Practices (BMPs) in agriculture and urban development activities to reduce siltation and contaminant input.
- Partner with the Department of Health and Environmental Control to develop or improve water removal guidelines for agricultural, civil or industrial purposes that protect American eels.
- Work with municipalities and landowners to direct forestry activities away from floodplain areas.
- Work with the United States Army Corps of Engineers to identify dredging protocols that consider the timing of eel migration.
- Revise eel regulations to limit harvest of any eel life stage or sub-population.
- To the extent possible, control and prevent further distribution of non-native blue and flathead catfish populations.
- Form an alliance with other state and federal agencies as well as NGOs to implement range wide conservation and management of American eel as described in the ASMFCIFMP.
- Partner with the South Atlantic Fishery Management Council (SAFMC) to promote implementation of the Fishery Management Plan for Pelagic Sargassum Habitat of the South Atlantic Region.
- Promote changes in water release protocols for dams that will restore or approximatenatural flow regimens and increase minimum flows.
- Institute permitting protocols for aquaculture and pet fish industries that require certification of the absence of diseases and parasites for all Anguilla species.
- Participate in interstate research examining the effects of oceanic changes on distribution of larval American eel and how these changes may be related to global warming.
- Develop education and outreach programs that distribute information to governments, civic groups, educational systems and NGOs about critical habitat needs, threats and potential conservation actions for the American eel.
In 2010, Greenpeace International has added the American eel to its seafood red list. "The Greenpeace International seafood red list is a list of fish that are commonly sold in supermarkets around the world, and which have a very high risk of being sourced from unsustainable fisheries."[41]
- ^ South Carolina Department of Natural Resources http://www.dnr.sc.gov/cwcs/pdf/AmericanEel.pdf
- ^ http://publications.gc.ca/collections/Collection/CW69-14-458-2006E.pdf
- ^ Berg 1949
- ^ Jordan and Evermann 1896
- ^ http://www.nefsc.noaa.gov/publications/series/shtsr/shltr17.pdf
- ^ US NOAA Biological Fisheries data ftp://ftp.fao.org/docrep/fao/009/y4161e/y4161e06.pdf
- ^ Tesch, F. W. 1977. The eel. J. Greenwood, translator. Chapman and Hal1, London. 422 pp.
- ^ Bertin, L. 1956. Eels: a biological study. Cleaver-Hume Press Ltd., London.197 pp.
- ^ a b Minckley, W. L. 1973. Fishes of Arizona. Arizona Fish and Game Department. Sims Printing Company, Inc., Phoenix, AZ.
- ^ Smith, H. M. 1896. A review of the history and results of the attempts to acclimatize fish and other water animals in the Pacific states. Pages 379-472 in Bulletin of the U.S. Fish Commission, Vol. XV, for 1895.
- ^ Gerking, S. D. 1945. Distribution of the fishes of Indiana. Investigations of Indiana Lakes and Streams 3:1-137.
- ^ Shute, P.W. and D.A. Etnier. 2000. Southeastern fishes council regional reports - 2000. Region III - North-Central.
- ^ Sigler, F. F., and R. R. Miller. 1963. Fishes of Utah. Utah Department of Fish and Game, Salt Lake City, UT. 203 pp.
- ^ Sigler, F. F., and R. R. Miller. 1963. Fishes of Utah. Utah Department of Fish and Game, Salt Lake City, UT. 203 pp.
- ^ [USGS.gov Pam Fuller and Leo Nico. 2012. Anguilla rostrata. USGS Nonindigenous Aquatic Species Database, Gainesville, FL. http://nas.er.usgs.gov/queries/factsheet.aspx?SpeciesID=310 Revision Date: 3/5/2011]
- ^ 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. www.nwrc.usgs.gov/wdb/pub/species_profiles/82_11-074.pdf
- ^ Jeffries, H.P. 1960. Winter occurrences of Anguilla rostrata elvers in New England and Middle Atlantic estuaries. Limnol. Oceanogr. 5:338- 340.
- ^ Barila, F. Y., and J. R. Stauffer, Jr. 1980. Temperature behavioral responses of the American eel, Anguilla rostrata (LeSeur), from Maryland. Hydrobiologio 74:49-51
- ^ Karlsson, L., G. Ekbohm, and G.Stein- holtz. 1984. Comments on a study of the thermal behaviour of the American eel (Anguilla rostrata) and some statistical suggestions for temperature preference studies Hydrobiologia 109:75-78.
- ^ Fahay, M. P. 1978. Biological and fisheries data on American eel, Anguilla rostrata (LeSueur). U. S. Natl. Mar. Fish. Serv. Tech. Ser.,Rep. No. 17, Northeast Fisheries Center, Highlands, N.J. 82 pp.
- ^ Fahay, M. P. 1978. Biological and fisheries data on American eel, Anguilla rostrata (LeSueur). U. S. Natl. Mar. Fish. Serv. Tech. Ser.,Rep. No. 17, Northeast Fisheries Center, Highlands, N.J. 82 pp.
- ^ American Eel: American Littoral Society- Species Spotlight http://www.littoralsociety.org/userfiles/doccenter/Species%20Spotlight%20american%20eel.pdf
- ^ Hatch, J.T. 2002. American Eel Angullia rostrata (Lesueur, 1817) member of the eel family Anguillidae. Retrieved from http://hatch.cehd.umn.edu/research/fish/fishes/american_eel.html
- ^ Hatch, J.T. 2002. American Eel Angullia rostrata (Lesueur, 1817) member of the eel family Anguillidae. Retrieved from http://hatch.cehd.umn.edu/research/fish/fishes/american_eel.html
- ^ Hatch, J.T. 2002. American Eel Angullia rostrata (Lesueur, 1817) member of the eel family Anguillidae. Retrieved from http://hatch.cehd.umn.edu/research/fish/fishes/american_eel.html
- ^ David, S. 2000. "Anguilla rostrata" (On-line), Animal Diversity Web. Accessed May 07, 2012 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Anguilla_rostrata.html
- ^ David, S. 2000. "Anguilla rostrata" (On-line), Animal Diversity Web. Accessed May 07, 2012 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Anguilla_rostrata.html
- ^ Hatch, J.T. 2002. American Eel Angullia rostrata (Lesueur, 1817) member of the eel family Anguillidae. Retrieved from http://hatch.cehd.umn.edu/research/fish/fishes/american_eel.html
- ^ Helfman, G. S., and J. B. Clark. 1986. Rotational feeding: over- coming gape-1 imited foraging i n anguillid eels. Copeia 1986:679-685.
- ^ Wenner, C. A., and J. A. Musick. 1975. Food habits and seasonal abundance of the American eel, Anguilla rostrata, from the lower Chesapeake Bay. Chesapeake Sci. 16:62-66
- ^ McCord, J. W. 1977. Food habits and elver miqratioc of American eel , Angui 11a -rostrata, (LeSueur) , i n Coo~erRiver, South Carolina. M.S. Thesis. ~elmson University, Clemson, S.C. 47 pp.
- ^ Hornberger, M. L., J. S. Tuten, A. Eversole, J. Crane, R. Hansen, and M. Hinton. 1978. Anierican eel investigations. Completion report f o r March 1977-July 1978. South Carolina Wi1dlife and Marine Research Department, Charleston, and Clemson University, Clemson. 311 pp
- ^ Sorensen, P. W., and M. L. Bianchini. 1986. Environmental correlates of the freshwater migration of elvers of the American eel in a Rhode Island brook. Trans. Am. Fish. Soc. 115:258-268.
- ^ Sinha, V. R. P., and J. W. Jones. 1967. On the food of the freshwater eels and their feeding relationship with salmonids. J. Zool . (Lond.) 153:119-137.
- ^ Based on data sourced from the FishStat database, FAO.
- ^ Fahay, M. P. 1978. Biological and fisheries data on American eel, Anguilla rostrata (LeSueur). U. S. Natl. Mar. Fish. Serv. Tech. Ser.,Rep. No. 17, Northeast Fisheries Center, Highlands, N.J. 82 pp.
- ^ Ontario NMR http://www.mnr.gov.on.ca/en/Business/SORR/2ColumnSubPage/EELPAGE.html
- ^ Hill, L. J. 1969. Reactions of the American eel to dissolved oxygen tensions. Tex. J. Sci. 20:305-313.
- ^ Hodson, P.V., M. Castonguay, C.M. Couillard, C. Desjardins, E. Pellitier and R. McLeod. 1994. Spatial and temporal variations in chemical contamination of American eel (Anguilla rostrata) captured in the estuary of the St. Lawrence River. Can. J. Fish. Aquat. Sci. 51:464-478.
- ^ Ontario NMR http://www.mnr.gov.on.ca/en/Business/LetsFish/2ColumnSubPage/STEL02_165908.html
- ^ Greenpeace International Seafood Red list
