American eel

The American eel (Anguilla rostrata) is a facultative catadromous fish found on the eastern coast of North America. Eels (Anguilla spp.) are fish belonging to the elopomorph superorder, a group of phylogenetically ancient teleosts.[2] 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 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 by 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 often lighter than those from dark, tannic acid streams.[3]

The eel lives in fresh water and estuaries and only leaves these habitats to enter the Atlantic Ocean to start its spawning migration to the Sargasso Sea.[4] Spawning takes place far offshore where the eggs hatch. The female can lay up to 4 million buoyant eggs a year, and dies after egg-laying. After the eggs hatch and the early-stage larvae develop into leptocephali, the young eels move toward North America where they metamorphose into glass eels and enter freshwater systems where they grow as yellow eels until they begin to mature.

The American eel is found along the Atlantic coast including Chesapeake Bay and the Hudson River and as far north as the St. Lawrence River region. It is also present in the river systems of the eastern Gulf of Mexico and in some areas further south. Like all anguillid eels, American eels hunt predominantly at night, and during the day they hide in mud, sand or gravel very close to shore, at depths of roughly 5 to 6 feet. They feed on crustaceans, aquatic insects, small insects, and probably any aquatic organisms that they can find and eat.[5]

American eels are economically important in various areas along the East Coast as bait for fishing for sport fishes such as the striped bass, or as a food fish in some areas. Their recruitment stage, the glass eel, are also caught and sold for use in aquaculture, although this is now restricted in most areas.

Eels were once an abundant species in rivers, and were an important fishery for aboriginal people. The construction of hydroelectric dams has blocked their migrations and locally extirpated eels in many watersheds. For example, in Canada, the vast numbers of eels in the St. Lawrence and Ottawa Rivers have dwindled.[6]

American eel
American Eel
American eel (Anguilla rostrata) (4015394951)
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Anguilliformes
Family: Anguillidae
Genus: Anguilla
Species:
A. rostrata
Binomial name
Anguilla rostrata
Lesueur, 1821
Rostratamuk
Range map

Etymology

The American eel Anguilla rostrata was first described in 1817 by Lesueur. Anguilla is Latin for eel, and rostrata is a Latin word that can mean either "beaked or curved" or "long nose". French: Anguille d'Amérique, Spanish: Anguila americana.

Description

Rostrata
Juvenile eels

American eels can grow to 1.22 m (4.0 ft) in length and to 7.5 kg (17 lb) in weight. Females are generally larger than males, lighter in color, with smaller eyes and higher fins.[7] The body is elongate and snake-like. Its dorsal and anal fins are confluent with the rudimentary caudal fin. It lacks ventral fins but pectoral fins are present. The lateral line is well-developed and complete. The head is long and conical, with rather small, well-developed eyes. The mouth is terminal with jaws that are not particularly elongated. The teeth are small, pectinate or setiform in several series on the jaws and the vomer. Minute teeth also present on the pharyngeal bones, forming a patch on the upper pharyngeals. Tongue present with thick lips that are attached by a frenum in front. Nostrils are superior and well separated. Gill openings are partly below pectoral fins, relatively well-developed and well separated from one another. Inner gill slits are wide.[8]

The scales are small, rudimentary, cycloid, relatively well embedded below the epidermis and therefore often difficult to see without magnification.[9] The scales are not arranged in overlapping rows as they often are in other fish species but are rather irregular, in some places distributed like "parquet flooring". In general, one row of scales lies at right angle to the next, although the rows immediately above and below the lateral line lie at an angle of approximately 45°. Unlike other bony fishes, the first scales do not develop immediately after the larval stage but appear much later on.[10]

Several morphological features distinguish the American eel from other eel species. Tesch (1977)[11] described three morphological characteristics which persist through all stages from larvae to maturing eels: the total number of vertebrae (mean 107.2), the number of myomeres (mean 108.2), and the distance between the origin of the dorsal fin to the anus (mean 9.1% of total length).

Distribution and natural habitat

Geographic range

The distribution of the American eel encompasses all accessible freshwater (streams and lakes), estuaries and coastal marine waters across a latitudinal range of 5 to 62 N.[12] Their natural range includes the eastern North Atlantic Ocean coastline from Venezuela to Greenland and including Iceland.[13] Inland, this species extends into the Great Lakes and the Mississippi River.[14]

Nonindigenous occurrences of this species in the United States were recorded from Lake Mead on the Colorado River and on the Arizona border.[15] It was stocked on a few occasions in Sacramento and San Francisco bay, California, in the late 1800s. No apparent evidence of survival on these occasions was noted.[16] It was also stocked and unintentionally introduced in various states, including Illinois, Indiana,[17] Nebraska, Nevada,[15] North Carolina,[18] Ohio and Pennsylvania,[19] and Wisconsin. Stocking of this species also occurred in Utah in the late 1800s, but soon disappeared.[19][20]

Natural habitat

Eels are bottom dwellers. They hide in burrows, tubes, snags, masses of plants, other types of shelters.[8] They are found in a variety of habitats including streams, rivers, and muddy or silt-bottomed lakes during their freshwater stage, as well as oceanic waters, coastal bays and estuaries.[6][13][14][21] Individuals during the continental stage occasionally migrate between fresh, salt and brackish water habitats and have varying degrees of residence time in each.[22][23][24] During winter, eels burrow under the mud and enter a state of torpor (or complete inactivity) at temperatures below 5 °C.[25] although they may occasionally be active during this period.[6] Temperature requirements are suggested to be flexible. It has been found that American eels during elver stage can survive temperature as low as −0.8 °C. Barila and Stauffer (1980) reported a final mean temperature preference at 16.7 °C. Karlsson et al. (1984) disagreed with this interpretation and found the final temperature preference of 17.4 ± 2.0 °C with a 95% confidence interval.

Seasonal patterns described by Fletcher and Anderson (1972) generalize annual movements from freshwater to estuaries and coastal bays to feed during spring, then either a return during the fall to overwinter (juvenile and immature adults), or a southward migration to the spawning grounds (silver eels Continental phase eels appear highly plastic in habitat use. Eels are extremely mobile and may access habitats that appear unavailable to them, using small watercourses or moving through wet grasses. Small eels (<100 mm total length) are able to climb and may succeed in passing over vertical barriers.[26] Habitat availability may be reduced by factors such as habitat deterioration, barriers to upstream migration (larger eels), and barriers (i.e. turbines) to downstream migration that can result in mortality.[6]

Life cycle

The American eel's complex life history begins far offshore in the Sargasso Sea in a semelparous and panmictic reproduction.[27][28][29] From there, young eels drift with ocean currents and then migrate inland into streams, rivers and lakes. This journey may take many years to complete with some eels travelling as far as 6,000 kilometers. After reaching these freshwater bodies they feed and mature for approximately 10 to 25 years before migrating back to the Sargasso Sea in order to complete their life cycle.[6]

Life stages are detailed below.[30]

1. Eggs: The eggs hatch within a week of deposition in the Sargasso Sea. McCleave et al. (1987) suggested that hatching peaks in February and may continue until April. Wang and Tzeng (2000) proposed, on the basis of otolith back-calculations, that hatching occurs from March to October and peaks in August. However, Cieri and McCleave (2000) argued that these back-calculated spawning dates do not match collection evidence and may be explained by resorption. 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.[31] The diameter of egg is about 1.1 mm. Fertilization is external, and adult eels are presumed to die after spawning. None has been reported to migrate up rivers.

2. Leptocephali: The leptocephalus is the larval form, a stage strikingly different from the adult form the eels will grow into. Leptocephali are transparent with a small pointed head and large teeth and are frequently described "leaf-like". The laterally compressed larvae are passively transported west and north to the coastal waters on the eastern coast of North America, by the surface currents of the Gulf Stream system, a journey that will last between 7 and 12 months.[11][28] Vertical distribution is usually restricted to the upper 350 m of the ocean. Growth has been evaluated at about 0.21 to 0.38 mm per day.

3. Glass eel: As they enter the continental shelf, leptocephali metamorphose into glass eels (juveniles), which are transparent and possess the typical elongate and serpentine eel shape. The term glass eel refers to all developmental stages between the end of metamorphosis and full pigmentation.[10] Metamorphosis occurs when leptocephali are about 55 to 65 mm long. Mean age at this metamorphosis has been evaluated at 200 days and estuarine arrival at 255 days; giving 55 days between glass eel metamorphosis and estuarine arrival. Young eels use selective tidal stream transport to move up estuaries. As they enter coastal waters, the animals essentially transform from a pelagic oceanic organism to a benthic continental organism.

4. Elvers: Glass eels become progressively pigmented as they approach the shore; these eels are termed elvers. The melanic pigmentation process occurs when the young eels are in coastal waters. At this phase of the life cycle, the eel is still sexually undifferentiated. The elver stage lasts about three to twelve months. Elvers that enter fresh water may spend much of this period migrating upstream. Elver influx is linked to increased temperature and reduced flow early in the migration season, and to tidal cycle influence later on.[11]

5. 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. Sexual differentiation occurs during the yellow stage and appears to be strongly influenced by environmental conditions. Krueger and Oliveira (1999) suggested that density was the primary environmental factor influencing the sex ratio of eels in a river, with high densities promoting the production of males. From life history traits of four rivers of Maine, Oliveira and McCleave (2000) evaluated that sexual differentiation was completed by 270 mm total length.

6. Silver eels: As the maturation process proceeds, the yellow eel metamorphoses into a silver eel. The silvering metamorphosis results in morphological and physiological modifications that prepare the animal to migrate back to the Sargasso Sea. The eel acquires a greyish colour with a whitish or cream coloration ventrally.[11][13] The digestive tract degenerates, the pectoral fins enlarge to improve swimming capacity, eye diameter expands and visual pigments in the retina adapt to the oceanic environment, the integument thickens,[11] percentage of somatic lipids increases to supply energy for migrating and spawning, gonadosomatic index and oocyte diameter increase, gonadotropin hormone (GTH-II) production increases, and osmoregulatory physiology changes.

Feeding

Eels are nocturnal and most of their feeding therefore occurs at night.[27] Having a keen sense of smell, eels most likely depend on scent to find food. The American eel is a generalist species which colonizes a wide range of habitats. Their diet is therefore extremely diverse and includes most of the aquatic animals sharing the same environment.

Leptocephalus

Little is known about the food habits of leptocephali. Recent studies on other eel species (Otake et al. 1993; Mochioka and Iwamizu 1996) suggest that leptocephali do not feed on zooplankton but rather consume detrital particles such as marine snow and fecal pellets or particles such as discarded houses of larvacean tunicates.

Glass eel and elver

Based on laboratory experiments on European glass eels, Lecomte-Finiger (1983) reported that they were morphologically and physiologically unable to feed. However, Tesch (1977) found that elvers at a later stage of pigmentation, stage VIA4, were feeding.[11] Stomach examination of elvers caught during their upstream migration in the Petite Trinité River on the north shore of the Gulf of St. Lawrence revealed that elvers fed primarily on insect larvae.

Yellow eel

The yellow eel is essentially a nocturnal benthic omnivore. Prey includes fishes, molluscs, bivalves, crustaceans, insect larvae, surface-dwelling insects, worms, frogs and plants. The eel prefers small prey animals which can easily be attacked.[11] Food type varies with body size.[11] Stomachs of eels less than 40 cm and captured in streams contained mainly aquatic insect larvae, whereas larger eels fed predominantly on fishes and crayfishes. Insect abundance decreased in larger eels. The eel diet adapts to seasonal changes and the immediate environment. Feeding activity decreases or stops during the winter, and food intake ceases as eels physiologically prepare for the spawning migration.[31]

Predation

Little information about predation on eels has been published. It was reported that elvers and small yellow eels are prey of 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]

Commercial fisheries

Wild capture of Anguilla rostrata
Global capture of American eel in tonnes reported by the FAO, 1950–2009[35]

The major outlet for US landings of yellow and silver eels is the EU market.[8]

In the 1970s, the annual North Atlantic harvest averaged 125,418 kg, with an average value of $84,000. In 1977, the eel landings from Maine, New Hampshire, and Massachusetts were about 79,700, 2,700, and 143,300 kg, 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 American eel has declined from approximately 223,000 kilograms (kg) in the early 1980s to 11,000 kg in 2002.[36]

Conservation

According to the International Union for Conservation of Nature, the American eel is at very high risk of extinction in the wild.[37][38]

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 species. The number of juvenile eels in the Lake Ontario area decreased from 935,000 in 1985 to about 8,000 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,[39] which is typically found below dams. Contaminations of heavy metals, dioxins, 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.[40] 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.

Conservation measures

The U.S. Fish and Wildlife Service reviewed the status of the American eel both in 2007 and in 2015, finding both times that Endangered Species Act protection for the American eel is not warranted.[41] 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.[42]

Sustainable consumption

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."[43]

References

  1. ^ Jacoby, D., Casselman, J., DeLucia, M., Hammerson, G.A. & Gollock, M. (2014). Anguilla rostrata. The IUCN Red List of Threatened Species. Version 2014.3
  2. ^ Nelson JS (1994) Fishes of the world. John Wiley and Sons, New York
  3. ^ McCord, John W. American Eel. South Carolina Department of Natural Resources
  4. ^ Nuwer, Rachel (December 7, 2015) Closing In on Where Eels Go to Connect. New York Times
  5. ^ NOAA Great Lakes Environmental Research Laboratory
  6. ^ a b c d e American Eel Anguilla rostrata in Canada. COSEWIC Assessment and Status Report 2006. ISBN 0-662-43225-8
  7. ^ Smit, D.G. Order ANGUILLIFORMES. National Museum of Natural History, Washington, D.C., USA
  8. ^ a b c Fahay, Michael P. (August 1978) Biological and Fisheries Data on. American eel, Anguilla rostrata (Lesueur). Sandy Hook Laboratory. US National Oceanic and Atmospheric Administration
  9. ^ Hardy, J.D., Jr. (1978) Development of Fishes of the Mid-Atlantic Bight: An Atlas of Egg, Larval, and Juvenile Stages. Volume II – Anguillidae thorough Syngnathidae. Fish and Wildlife Service, U.S. Department of the Interior.
  10. ^ a b Tesch F.W. (2003). The eel. Third Edition. Blackwell Science. ISBN 0632063890
  11. ^ a b c d e f g h Tesch, F.W. (1977). The eel: biology and management of anguillid eels. Chapman and Hall, London
  12. ^ Bertin, L. (1956). Eels: a biological study. Cleaver-Hume Press Ltd., London.
  13. ^ a b c Scott, W.B. and E.J. Crossman. (1973) Freshwater fishes of Canada. Bulletin 184, Fisheries Research Board of Canada, Ottawa. The Bryant Press Limited, Ottawa, ON.
  14. ^ a b Jessop, B.M. (2006) Underwater world: American Eel. Communications Directorate, Fisheries and Oceans Canada, Ottawa, ON.
  15. ^ a b Minckley, W. L. (1973). Fishes of Arizona. Arizona Fish and Game Department. Sims Printing Company, Inc., Phoenix, AZ.
  16. ^ 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", pp. 379–472 in Bulletin of the U.S. Fish Commission, Vol. XV, for 1895.
  17. ^ Gerking, S. D. (1945). "Distribution of the fishes of Indiana". Investigations of Indiana Lakes and Streams. 3: 1–137.
  18. ^ Shute, P.W. and D.A. Etnier. (2000). Southeastern fishes council regional reports – 2000. Region III – North-Central.
  19. ^ a b Sigler, F. F., and R. R. Miller. (1963). Fishes of Utah. Utah Department of Fish and Game, Salt Lake City, UT.
  20. ^ Fuller, Pam and Nico, Leo (2012) Anguilla rostrata. USGS Nonindigenous Aquatic Species Database, Gainesville, FL.
  21. ^ Scott, W.B and Scott, M.G. (1988) "Atlantic fishes of Canada". Canadian Bulletin of Fisheries and Aquatic Sciences 219.
  22. ^ Fletcher, G.L. and T. Anderson. (March 1972). "A preliminary survey of the distribution of the American Eel (Anguilla rostrata) in Newfoundland". MSRL Technical Report No. 7. Marine Sciences Research Laboratory, St. John's, NL.
  23. ^ Clarke, K.D., R.J. Gibson and D.A. Scruton. (January 2007). "A review of the habitat associations and distribution of the American Eel within Newfoundland and Labrador". Presentation at the Canadian Conference for Fisheries Research.
  24. ^ Jonsson, B.; Jessop, B. M. (2010). "Geographic effects on American eel (Anguilla rostrata) life history characteristics and strategies". Canadian Journal of Fisheries and Aquatic Sciences. 67 (2): 326–346. doi:10.1139/F09-189.
  25. ^ Walsh, P.J.; Foster, G.D.; Moon, T.W. (1983). "The effects of temperature on metabolism of the American Eel Anguilla rostrata (LeSueur): compensation in the summer and torpor in the winter". Physiological Zoology. 56 (4): 532–540. doi:10.1086/physzool.56.4.30155876. JSTOR 30155876.
  26. ^ Legault, A (1988). "Le franchissement des barrages par l'escalade de l'anguille: étude en Sèvre Niortaise" (PDF). Bulletin Français de la Pêche et de la Pisciculture. 308: 1–10.
  27. ^ a b Helfman, G.S., D.E. Facey, L.S. Hales, Jr., and E.L Bozeman, Jr. (1987). "Reproductive ecology of the American Eel". pp. 42–56 in M.J. Dadswell, R.L. Klauda, C.M. Moffitt, R.L. Saunders, R.A. Rulifson, and J.E. Cooper (eds.) Common strategies of anadromous and catadromous fishes. American Fisheries Society Symposium 1, Maryland.
  28. ^ a b Schmidt, J. (1922). "The breeding places of the eel". Philosophical Transactions of the Royal Society of London, Series B. 211 (382–390): 179–208. doi:10.1098/rstb.1923.0004. JSTOR 92087.
  29. ^ Wirth, T; Bernatchez, L (2003). "Decline of North Atlantic eels: A fatal synergy?". Proceedings of the Royal Society B: Biological Sciences. 270 (1516): 681–8. doi:10.1098/rspb.2002.2301. PMC 1691294. PMID 12713741.
  30. ^ Species Spotlight: American eel (Anguilla rostrata). American Littoral Society
  31. ^ a b Wenner, C. A.; Musick, J. A. (1975). "Food Habits and Seasonal Abundance of the American eel, Anguilla rostrata, from the Lower Chesapeake Bay". Chesapeake Science. 16: 62. doi:10.2307/1351085. JSTOR 1351085.
  32. ^ Hornberger, M. L., J. S. Tuten, A. Eversole, J. Crane, R. Hansen, and M. Hinton. (1978) "Anierican eel investigations". Completion report for March 1977 – July 1978. South Carolina Wi1dlife and Marine Research Department, Charleston, and Clemson University, Clemson.
  33. ^ Sorensen, P. W.; Bianchini, M. L. (1986). "Environmental Correlates of the Freshwater Migration of Elvers of the American Eel in a Rhode Island Brook". Transactions of the American Fisheries Society. 115 (2): 258–268. doi:10.1577/1548-8659(1986)115<258:ECOTFM>2.0.CO;2.
  34. ^ Sinha, V. R. P.; Jones, J. W. (2009). "On the food of the freshwater eels and their feeding relationship with the salmonids". Journal of Zoology. 153: 119–137. doi:10.1111/j.1469-7998.1967.tb05034.x.
  35. ^ Based on data sourced from the FishStat database, FAO.
  36. ^ American Eel in Ontario. mnr.gov.on.ca
  37. ^ "American Eel Is in Danger of Extinction". Scientific American. December 1, 2014.
  38. ^ "Anguilla rostrata". International Union for Conservation of Nature.
  39. ^ Hill, L. J. (1969). "Reactions of the American eel to dissolved oxygen tensions". Tex. J. Sci. 20: 305–313.
  40. ^ Hodson, P. V.; Castonguay, M.; Couillard, C. M.; Desjardins, C.; Pelletier, E.; McLeod, R. (1994). "Spatial and Temporal Variations in Chemical Contamination of American Eels, Anguilla rostrata, Captured in the Estuary of the St, Lawrence River". Canadian Journal of Fisheries and Aquatic Sciences. 51 (2): 464–478. doi:10.1139/f94-049.
  41. ^ "The American Eel". U.S. Fish & Wildlife Service.
  42. ^ Protecting the Vanishing American Eel. mnr.gov.on.ca
  43. ^ Greenpeace International Seafood Red list Archived August 20, 2010, at the Wayback Machine. greenpeace.org

External links

Anguillidae

The Anguillidae are a family of ray-finned fish that contains the freshwater eels. Eighteen of the nineteen extant species and six subspecies in this family are in the genus Anguilla. They are elongated fish with snake-like bodies, their long dorsal, caudal and anal fins forming a continuous fringe. They are catadromous fish, spending their adult lives in fresh water but migrating to the ocean to spawn. Eels are an important food fish and some species are now farm-raised but not bred in captivity. Many populations in the wild are now threatened and Seafood Watch recommend consumers avoid eating anguillid eels.

Anguilloidei

The Anguilloidei are a suborder of the order Anguilliformes (the eels) containing three families:

Anguillidae (freshwater eels)

Serrivomeridae (sawtooth eels)

Nemichthyidae (snipe eels)This suborder traditionally included several other families that have recently been moved to new suborders:

Chlopsidae (false morays), Heterenchelyidae (mud eels), Moringuidae (worm eels), Muraenidae (moray eels), and Myrocongridae (thin eels).

Ashuelot Pond

Ashuelot Pond is a 368-acre (149 ha) water body located in Sullivan County in western New Hampshire, United States, in the town of Washington. It is situated along the upper reaches of the Ashuelot River, a tributary of the Connecticut River.

The pond is good for boating, fishing, and wildlife watching. Personal water craft with a capacity of two passengers or less are prohibited by the state of New Hampshire. The pond mostly has a muddy bottom.

The lake is classified as a warmwater fishery, with observed species including smallmouth bass, largemouth bass, chain pickerel, yellow perch, pumpkinseed, horned pout, and American eel.Pond associations include the Ashuelot Pond Association and the LAE Association.

Belleisle Bay

Belleisle Bay is a fjord-like branch of the Saint John River in the Canadian province of New Brunswick

Species of fish common to the area include, among others:

Yellow perch

White perch

Smallmouth bass

American eel

Lamprey eel

Pumpkin seed sunfish

Brown bull head catfish

Yellow bull head catfish

White bull head catfish

Southern channel catfish (a very rare catch in Canada)

Chain pickerel

Muskey (also rare)

Sturgeon

Stripped bass

Brown trout

Atlantic salmon

Central New England Fishery Resource Office

The Central New England Fishery Resource Office is involved in programs to restore, enhance, and manage a number of migratory fish species and the habitats they depend upon. Species of primary concern include American shadalewife, blueback herring, Atlantic salmon and American eel. Programs include fish population assessments, hatchery product evaluations, habitat restoration, fish trap and transfer, and movement studies.

Staff participate on technical, policy, and assessment committees and related work groups involving fish passage issues, dam removals, restoration planning, and restoration evaluations. Activities are conducted in collaboration with state and federal agencies, watershed groups, fishing clubs, and other non-government organizations. The office conducts assessments and develops management plans for aquatic resources on Service and other federal lands.

China Lake (Maine)

China Lake is a pond in Kennebec County, Maine. Located northeast of the state capital of Augusta, China Lake is situated in the towns of China and Vassalboro. China Lake has two large basins connected by a narrow neck. The elongated eastern basin with an average depth of less than 30 feet (9.1 m) is entirely within the town of China, and has an irregular shoreline heavily developed with residences and seasonal cottages. The more nearly circular western basin extending into East Vassalboro is as deep as 85 feet (26 m), and shoreline development around the western basin has been discouraged to allow use as a water supply for Waterville and Winslow. The western basin overflows into Outlet Stream in the town of Vassalboro. Outlet Stream flows 7 miles (11 km) north to discharge into the Sebasticook River in Winslow 1 mile (1.6 km) upstream of the Kennebec River.Summer water temperatures in China Lake range from 72° near the surface to 48° in the deepest pools. Nutrient loading from shoreline development causes annual algal blooms with nocturnal depression of dissolved oxygen concentrations. These conditions have become unsuitable for historic populations of Atlantic salmon and lake trout. Introduced brown trout have adapted to lake conditions, and brook trout fishing has been sustained by stocking legal-size fish from surplus hatchery production. Fishermen seeking trout, chain pickerel, white perch, or smallmouth and largemouth bass may also catch yellow perch, sunfish, creek chub, white sucker, hornpout, or American eel. Public boat launch facilities are available at the north end of the eastern basin and in Vassalboro near the outlet of the western basin.

Cliff Pond

Cliff Pond is a 204-acre (830,000 m2) kettle pond in Brewster, Massachusetts. It is the largest pond in Nickerson State Park and is quite popular with swimmers and fishermen in summer months.

Cliff Pond was totally reclaimed in 1960 and, like many kettle ponds has been treated for alkalinity over the years. The Massachusetts Division of Fisheries and Wildlife stocks the pond in spring and fall with various trout species. It also has smallmouth bass and various other species. In 1992, a world record American eel (8 pounds, 9 ounces, 46 inches

long, 10.5 inches in girth) was caught.The pond has had repeated problems with bluegreen algae blooms causing closures over the years and was treated in spring 2016 with aluminum sulfate. Water transparency has improved and the treatment is expected to last twenty years.

Country Pond

Country Pond is a 306-acre (124 ha) water body located in Rockingham County in southern New Hampshire, United States, in the towns of Kingston and Newton. Water from Country Pond flows via the Powwow River to the Merrimack River in Amesbury, Massachusetts.

The lake is classified as a warmwater fishery, with observed species including smallmouth bass, largemouth bass, chain pickerel, brown bullhead, black crappie, white perch, American eel, bluegill, white sucker, and pumpkinseed.

East Grand Lake

East Grand Lake is located between the U.S. state of Maine and the Canadian province of New Brunswick. The boundary between the United States and Canada passes through the lake. In Maine it falls within two counties, Washington and Aroostook, and in New Brunswick it serves as the western boundary of York County.

The lake is part of the Chiputneticook chain of lakes which also include Spednic, North, and Palfrey and form the headwaters of the St. Croix River. Formerly they were called the Shoodic Lakes.

East Grand Lake is famous for its quality fishing and scenic beauty. The lake is 22 miles (35 km) long and 4 miles (6 km) in width at its widest point. The maximum depth of the lake is 128 ft (39 m).

Fishing is very popular on East Grand Lake. The lake is home to several species including landlocked salmon, lake trout, yellow perch, white perch, smallmouth bass, American eel, brook trout, and many more.

Eel

An eel is any ray-finned fish belonging to the order Anguilliformes (), which consists of four suborders, 20 families, 111 genera, and about 800 species. Eels undergo considerable development from the early larval stage to the eventual adult stage, and most are predators. The term “eel” originally referred to the European eel, and the name of the order means “European eel-shaped.”

The term “eel” is also used for some other eel-shaped fish, such as electric eels (genus Electrophorus), spiny eels (family Mastacembelidae), and deep-sea spiny eels (family Notacanthidae). These other clades, however, evolved their eel-like shapes independently from the true eels.

Eel life history

The eel is a long, thin bony fish of the order Anguilliformes. Because fishermen never caught anything they recognised as young eels, the life cycle of the eel was a mystery for a very long period of scientific history. Although more than 6500 publications mention eels, much of their life history remains an enigma.

The European eel (Anguilla anguilla) was historically the one most familiar to Western scientists, beginning with Aristotle, who wrote the earliest known inquiry into the natural history of eels. He speculated that they were born of "earth worms", which he believed were formed of mud, growing from the "guts of wet soil" rather than through sexual reproduction. Many centuries passed before scientists were able to demonstrate that such spontaneous generation does not occur in nature.

Other early scientists believed that the eelpout Zoarces viviparus was the "mother of eels" (the translation of the German name "Aalmutter").

Green Branch (Patuxent River)

The Green Branch of the Patuxent River in Prince George's County, Maryland is part of the Upper Patuxent Watershead. The stream passes centrally through the Governor Bridge Natural Area / Patuxent River Park and joins the Patuxent, just south of Governor's Bridge.

The stream cuts a narrow gorge through the Aquia greensand between Crain Highway and its junction with the Patuxent.

Panmixia

Panmixia (or panmixis) means random mating.A panmictic population is one where all individuals are potential partners. This assumes that there are no mating restrictions, neither genetic nor behavioural, upon the population, and that therefore all recombination is possible. The Wahlund effect assumes that the overall population is panmictic.In genetics, random mating involves the mating of individuals regardless of any physical, genetic, or social preference. In other words, the mating between two organisms is not influenced by any environmental, hereditary, or social interaction. Hence, potential mates have an equal chance of being selected. Random mating is a factor assumed in the Hardy-Weinberg principle and is distinct from lack of natural selection: in viability selection for instance, selection occurs before mating.

Patapsco River

The Patapsco River mainstem is a 39-mile-long (63 km) river in central Maryland which flows into the Chesapeake Bay. The river's tidal portion forms the harbor for the city of Baltimore. With its South Branch, the Patapsco forms the northern border of Howard County, Maryland. The name "Patapsco" is derived from the Algonquian pota-psk-ut, which translates to "backwater" or "tide covered with froth."

Pearly Lake

Pearly Lake or Pearly Pond is a 192-acre (0.8 km2) water body in the town of Rindge, Cheshire County, southwestern New Hampshire, United States. Formerly known as Tarbell Pond, named for Revolutionary War Minuteman Lieut. Samuel Tarbell (1744-1828) who settled here, the lake is one of the headwaters of Tarbell Brook, a tributary of the Millers River, which flows southwest to the Connecticut River at Millers Falls, Massachusetts.The undergraduate campus of Franklin Pierce University is located on the northeast shore of the lake.

The lake is classified as a warmwater fishery, with observed species including largemouth bass, chain pickerel, yellow perch, bluegill, horned pout, American eel, and green sunfish.

Round Valley Reservoir

The Round Valley Reservoir in Clinton Township in Hunterdon County, New Jersey, United States, was formed in 1960 when the New Jersey Water Authority constructed two large dams and flooded a large valley. The reservoir is named after the naturally formed circular valley surrounded by Cushetunk Mountain. The deep valley was caused by erosion of the soft sedimentary rock. The surrounding ridges of Cushetunk Mountain endure because they were underlaid with dense and durable volcanic rock diabase that cooled slowly under the surface of the earth.

Reaching depths of 180 feet (55 m), this 2,350 acres (9.5 km2) reservoir is best known for its pristine clear blue waters. The reservoir contains 55 billion US gallons (210,000,000 m3) of water for use in central New Jersey, making it the largest in the state. Its water is distributed during times of drought via the nearby south branch of the Raritan River. The New Jersey Division of Wildlife (a department of the New Jersey Department of Environmental Protection) claims the reservoir is the southernmost body of water that contains naturally reproducing lake trout. This is one of only two lakes in New Jersey with lake trout, the other being Merrill Creek Reservoir in Warren County. Some of the other species of fish in the lake include bass, pickerel, catfish, american eel, yellow perch, brown trout, and rainbow trout. The park also has a wilderness area for camping, swimming and SCUBA diving facilities, a boat ramp and nature hiking and biking trails. The reservoir has been called the Bermuda Triangle of New Jersey, and over 26 people have drowned there since 1971. Six of them have never been found.

Saugatuck Reservoir

The Saugatuck Reservoir is a reservoir in Fairfield County, Connecticut, US, that straddles the border between the towns of Redding and Weston. It is created by the Samuel P. Senior dam of the Saugatuck River, and provides water to several of the surrounding towns. It is considered quite scenic and is stocked with trout for fishing. It borders the Trout Brook Valley State Park Reserve at the southeast.

Bridgeport Hydraulic Company Holdings (now owned by Aquarion) flooded the Saugatuck River Valley after 1938 displacing the villages of Hull and Valley Forge to create the Saugatuck Reservoir.Aquarion Water Co., owner of the reservoir and dam, allows tailrace fishing in one area at the Weston end of the reservoir, where it has constructed a handicapped-access area. However, anglers must obtain a permit from Aquarion before fishing in the Saugatuck.The Saugatuck is the largest of the eight reservoirs that make up Aquarion’s greater Bridgeport water system. It holds about 12 billion US gallons (45,000,000 m3) of water.The following fish species may be found within the Saugatuck Reservoir:

American eel

Bluegill (Sunfish)

Brook trout

Brown trout

Bullhead catfish

Chain pickerel

Crappie

Largemouth bass

Pumpkinseed (Sunfish)

Rainbow trout

Rock bass

Smallmouth bass

Walleye

White perch

Yellow perch

Saylorville Lake

Saylorville Lake is a reservoir on the Des Moines River in Iowa, United States. It is located 11 miles (18 km) upstream from the city of Des Moines, and 214 miles (344 km) from the mouth of the Des Moines River at the Mississippi River. It was constructed as part of a flood control system for the Des Moines River as well as to aid in controlling flood crests on the Mississippi, of which the Des Moines is a tributary. The lake and dam is owned and operated by the U.S. Army Corps of Engineers, Rock Island District.

At its normal level of 836 feet (255 m) above sea level, Saylorville Lake covers an area of 5,950 acres (24 km2) or 9.3 square miles (24.1 km2) and reaches some 17 miles (27 km) upstream. At full flood stage the lake can reach 16,700 acres (68 km2) or 26.1 square miles (67.6 km2) and reach 54 miles (87 km) long. At this point any further flow into the lake is channelled over an emergency spillway to the west of the main dam structure. The record high stage for the reservoir was 892.03 feet (271.89 m) above sea level set on July 11, 1993 during the Great Flood of 1993.

Construction of the Saylorville Dam was authorized by Congress in 1958. Excavation began at the site in July 1965, becoming fully operational in September 1977. The dam itself is 6,750 feet (2,057 m) long, 105 feet (32 m) tall, and 44 feet (13 m) wide at the top.

The lake is utilized for many recreational activities in the central Iowa area as well, as there is a large state park infrastructure surrounding the area of the lake, notably Jester Park and Big Creek State Park. The Corps of Engineers operates several recreation areas, campgrounds, and boat ramp facilities around the lake. Boating and swimming are very popular, as are camping, deer and game bird hunting, fishing, hiking, biking and disc golf. Coast Guard Auxiliary Flotilla 4 provides boating safety education and free vessel safety checks to boaters in the area.

Fish species that can be found in the lake include crappie, bluegill, green sunfish, largemouth bass, smallmouth bass, brown trout, northern pike, common carp, white bass, walleye, yellow bass, american eel, flathead catfish, channel catfish, bullheads, and hybrid striped bass

Undulatory locomotion

Undulatory locomotion is the type of motion characterized by wave-like movement patterns that act to propel an animal forward. Examples of this type of gait include crawling in snakes, or swimming in the lamprey. Although this is typically the type of gait utilized by limbless animals, some creatures with limbs, such as the salamander, choose to forgo use of their legs in certain environments and exhibit undulatory locomotion. This movement strategy is important to study in order to create novel robotic devices capable of traversing a variety of environments.

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