American Eel
Anguilla rostrata
Summary 2
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. 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...
Diagnostic description 3
Head rather long; eyes small and placed well forward on head. Lips thick. Caudal vertebrae without transverse processes. Premaxillae not developed as distinct elements in adults. Frontal bones paired, not grown together. Pectoral girdle with 7 to 9 (up to 11 in the young) radial elements. Adults usually white or light-colored below and brownish to blue-black above, but coloration is variable; young with some yellow on the edges of the dorsal and anal fins (Ref. 30499). Caudal fin rounded, joined to dorsal and anal fins. Gill opening on side in front of lower half of well-developed pectoral fin; lower jaw longer than upper; 103-111 vertebrae (Ref. 26938).
Distribution 4
Northwest to western Central Atlantic: Greenland south along the Atlantic coast of Canada and the USA to Panama, and throughout much of the West Indies south to Trinidad.
Habitat 5
Anadromous; born in Sargasso Sea, drift for one year to North American waters, live in flowing streams for several years, spawn in Sargasso Sea.
Habitat 6
A. rostrata live in freshwater as adults, usually in larger rivers or lakes, primarily swimming near the bottom in search of food. The species prefers to hunt at night and resides in crevices or other shelter from the light during the day, often times burying themselves in the substrate, whether mud, sand or gravel (Landau, 1992).
Aquatic Biomes: lakes and ponds; rivers and streams; coastal
Life cycle 7
Undertakes migration in autumn to the Sargasso Sea where spawning is said to take place. Coloration changes with sexual maturation. Dorsal surface of the pectorals becomes dark, lateral line becomes prominent, eye diameter increases and visual pigments change, body takes on a silvery bronze coloration. Females are usually larger than males and migrate much farther upstream (Ref. 57533). Adults die after spawning (Ref. 30499).Spawn at sea but growth occurs in estuaries or freshwater (Ref. 7135). Spawning grounds believed to be between 20° and 30°N and 60°and 75°W (Ref. 40916, 40917).
Morphology 8
Elongate, snakelike body with a small, pointed head. A. rostrata has no pelvic fins, but has one long dorsal fin that extends more than half of the body; dorsal fin is continuous with the caudal and anal fin. The lower jaw projects beyond upper jaw. One small gill slit is found in front of each pectoral fin. Coloration is variable with maturity level, the larval stage is called a leptocephalus, or glass eel. This stage is transparent and leaf-shaped with a prominent black eye. The leptocephalus develops into an elver, characterized by a darker coloring, from gray to greenish brown (Page & Burr, 1991). The next stage, the yellow eel, is the adult form that lives in freshwater; color ranges from yellow to olive-brown. Sexually mature adults, silver eels, are dark brown and gray dorsally, with a silver to white ventral side. Large eyes are prominent in silver eels. Individuals reach lengths up to 152 cm (Page & Burr, 1991).
Other Physical Features: bilateral symmetry
Average mass: 4031.5 g.
Nature serve conservation status 9
Rounded Global Status Rank: G4 - Apparently Secure
Reasons: Very large range in the Atlantic Ocean and estuaries and rivers of the Atlantic and Gulf coasts of the United States and southeastern Canada, as well as much of the Mississippi River basin and the West Indies and Caribbean regions; hundreds of occurrences or subpopulations; total adult population size likely exceeds 1 million but appears to be decreasing; factors possibly contributing to the decline include barriers to migration, habitat loss and alteration, hydroturbine mortality, oceanic conditions, overfishing, predation, parasitism, and pollution. Better information is needed on the current trend and the relative importance of the various threats.
Intrinsic Vulnerability: Highly vulnerable
Comments: American eels are slow to mature (7 to 30+ years) and reproduce only once during their lifetime. However, individual females often produce millions of eggs.
Environmental Specificity: Broad. Generalist or community with all key requirements common.
Other Considerations: The current status of the American eel is poorly understood, due to limited and (until recently) nonstandardized assessment efforts and protocols across the range of the species (American Eel Plan Development Team 2000). In the past, sampling programs in most jurisdictions were not designed to monitor the abundance of American eels, and resulting survey data may not adequately reflect trends in American eel populations. A widespread concern about the status of various local eel stocks reflects more the absence of knowledge about the stocks rather than a well-founded knowledge of decline (American Eel Plan Development Team 2000).
Because eels have been harvested along the Atlantic coast of the United States for many decades (see Jessop 1997 for a concise summary of the status of the U.S. American eel fishery), harvest data might serve as a source of information applicable to trend determination. Unfortunately, standardized harvest data are often not available, and existing data sets generally are for brief time periods or do not account for fishing effort. Furthermore, harvest data are often a poor indicator of abundance, because harvest is dependent on demand and may consist of annually changing mixes of year classes (American Eel Plan Development Team 2000).
For the past few years, standardized sampling and record keeping have been initiated under the auspices of the Atlantic States Marine Fisheries Commission. Resulting data eventually should allow a better assessment of trends in American eel populations.
Overall Status. Etnier and Starnes (1993) stated that American eels remain "fairly common in Atlantic and eastern Gulf coastal areas, but impoundments on most rivers in central North America may have reduced inland eel populations."
The Southeastern Fishes Council Technical Advisory Committee (Warren et al. 2000) categorized the American eel as "currently stable" in the southeastern and south-central United States. This category was defined as "a species or subspecies whose distribution is widespread or stable or a species or subspecies that may have declined in portions of its range but is not in need of immediate conservation management actions."
ATLANTIC COAST, CANADA TO SOUTHERN FLORIDA
Data from resource and fisheries agencies along the Atlantic coast of the United States and Canada suggest that there was a broad decline in eel abundance since the early 1980s (Richkus and Whalen 2000).
Indications from commercial harvest data. Eel catches in Ontario, Quebec, Prince Edward Island, and rivers of New Brunswick and Nova Scotia draining into the Gulf of St. Lawrence have declined since the mid-1980s (Fishes and Oceans Canada, Jessop 2000). The St. Lawrence River-Lake Ontario system accounts for 57% of the commercial catch. Throughout the 1990s, all provincial catches associated with this region "showed a synchronous exponential decline," with a combined catch in the late 1990s that was 59% below the long-term mean (Casselman 2001).
Commercial landings of American eel in the Atlantic coastal states (Maine to Florida) peaked in the mid-1970s at 3.5 million pounds but have since declined significantly to a near record low of 868,215 pounds in 2001 (National Marine Fisheries Service, Fisheries Statistics and Economics Division; ASMFC Fisheries Focus 12(1), March 2003). Catches averaged 2,540,599 pounds between 1970 and 1984 and 1,356,434 pounds between 1985 and 1998. The significance of these data is uncertain because corresponding information on the level of fishing effort is not available. Commercial landings fluctuate widely with market demand and so may not reflect changes in eel abundance.
Annual trends in reported eel catches by individual states (NMFS Fisheries Statistics and Economics Division) comprise three basic groups: declining catch (e.g., Rhode Island, New York); increasing catch (e.g., New Jersey, Delaware, Maryland); and catches that have returned to values typical of those reported prior to the peak catches of the 1970s and early 1980s (e.g., Maine, Massachusetts, Florida). Reported catches in some states declined sharply in 1996 but catch data may be incomplete (American Eel Plan Development Team 2000).
Landings in recent decades in Maine peaked in the 1970s at about 176,000-191,000 pounds. By 2000-2004, landings had declined to about 13,000-35,000 pounds (data from Maine Department of Marine Resources).
In Massachusetts, catches periodically have been much higher in the past than they are now, but they vary with the economy and demand and are not a reliable indicator of eel abundance (Hartel et al. 2002).
In New York, there is a commercial eel fishery in the upper Delaware system, but no readily identifiable trend is evident in the catch (Wayne P. Elliot, pers. comm., 2005). Subjective impressions are that the commercial eel catch is relatively stable (Norm McBride, pers. comm., 2005).
Dramatic evidence for the impact of major dams on eel abundance can be found in the Susquehanna River basin. Prior to completion of four mainstem dams on the lower Susquehanna (the last, Conowingo Dam, was built in 1928), eels were common throughout the Susquehanna basin and were popular with anglers in Pennsylvania lakes (Pennsylvania Commission of Fisheries 1897). Annual harvests of eels in the Susquehanna were nearly 1 million pounds at that time (J. Foster, pers. comm., 1995). For many decades, there have been no recreational or commercial harvests of this species in Pennsylvania. Source: U.S. Environmental Protection Agency, Mid-Atlantic Environmental Assessment (http://www.epa.gov/maia/html/mbss-ch4.html).
The commercial catch in the Chesapeake Bay area declined considerably between 1980 (318,000 kg reported by both Maryland and Virginia) and 1990 (54,000 kg in Maryland and 136,000 kg in Virginia) (Murdy et al. 1997). Trends in eel abundance may vary with location. Geer (2003) reported declines in the lower Chesapeake Bay, whereas Weeder and Uphoff (2003) concluded that commercial landings are either stable or possibly increasing in the upper Chesapeake Bay.
Recreational harvest data. For the most part, eels are caught incidentally by recreational hook and line anglers fishing for other species. A large proportion of the eels caught are released alive. American eels are often collected in minnow traps for use as bait by recreational anglers fishing for striped bass, bluefish, and other species.
The NMFS Marine Recreational Fisheries Statistics Survey (MRFSS), which has surveyed recreational catch in ocean and coastal waters since 1981, shows a declining trend in the eel catch during the latter part of the 1990s. For the Atlantic coast area surveyed, the estimated total annual catch ranged from 212,690 eels per year in 1982 to 36,741 per year in 1997. Recreational harvest in 2001 was 10,805 eels, down an order of magnitude from the peak in the early 1980s.
Fishery-Independent Monitoring. Fishery-independent surveys in the United States and Canada indicate declining or stable numbers in all sampled watersheds; no survey showed an increasing trend (Haro et al. 2000).
A few long-term data sets from fish ladders are available, and these suggest a decline in eel abundance. A severe decline has occurred in the number of eels ascending the eel ladder at the Moses-Saunders Dam (Ontario-New York) during the peak spring migration in the St. Lawrence River-Lake Ontario segment of the range (Castonguay et al. 1994, Casselman et al. 1997, Tremblay 2005). The number of juvenile eels climbing the eel ladder declined from more than one million per year in the early 1980s to fewer than 4,000 per year in the late 1990s and to level approaching zero by 2001. Over the past 20 years (or one generation), the decline exceeds 99 percent (Tremblay 2005). However, the decline in eel counts may be an artifact of lock/water flow usage at the Beauharnois Dam, which is downstream from the Moses-Saunders facility (American Eel Plan Development Team 2000).
A trend analysis of eel migration data for 1984-1995 (including data from the Moses-Saunders eel ladder) found significant negative trends for yellow and/or silver eel abundance in Ontario, Quebec, New York, and Virginia (Richkus and Whalen 1999). Richkus and Whalen found no significant trends for glass eels or elvers, but those data sets were generally not complete and may not have covered the years where the largest declines were observed in other data sets (Richkus and Whalen 1999). Overall, Richkus and Whalen (1999) concluded that there is broad-based evidence for a stock-wide abundance decline of American eel from 1984 to 1995.
Annual counts of migrating fish in the Connecticut River have tallied fewer eels in recent years. In 2002, at all dams on the river up to Holyoke, 275 eels were counted. More recently, counts were as follows: 25 in 2003, 1 in 2004, and none in 2005 (as of July). Eel counts in an eelway in the Westfield River (Connecticut River basin) in Massachusetts have been relatively consistent (roughly 300-500) since the eelway was constructed in 2001 (Caleb Slater, pers. comm., 2005).
A young-of-the-year abundance survey in the Jones River, Kingston, Massachusetts, showed no clear trend in eel abundance for the period 2000-2005 (Chase 2005).
Long-term data (1974 through 1996) from the Conowingo Dam fish lift on the Susquehanna River in Maryland showed a decline in elver counts after the early 1980s (J. Weeder, pers. comm.).
Elver abundance in South Carolina shows no indication of decline over the past few years, and many eels have been seen recently in electrofishing efforts in that state (Mark R. Collins, pers. comm., 2005).
In Florida, annual young-of-the-year sampling was initiated a few years ago at the Guana River Dam and Rodman Reservoir Dam (Bonvechio et al. 2004), but data obtained thus far are insufficient for trend determination.
Miscellaneous and anecdotal reports. George (1981) reported that eel abundance has apparently declined in the Adirondack region of New York, presumably as a result of dams that block eel movements.
In Virginia, eel populations have been largely eliminated in the upper James drainage, much of the middle James, and the upper and middle Roanoke River as a result of dam construction (Jenkins and Burkhead 1994). However, Roghair and Nuckols (2005) recently recorded eel densities of 80-510 eels per hectare in mountain streams in the James River drainage.
In Virginia, annual electrofishing (approximately 1 hour of electrofishing at each location) was conducted in the James River between Scottsville (rkm 304) and the headwaters near Iron Gate (rkm 555) in October-November from 1991-2004 (except 2002). The number of eels caught per year was small (range 13 to 209), with a general increasing trend from 1991 to 2000. [Data from Scott M. Smith, Virginia Department of Game and Inland Fisheries]
Populations of diadromous fishes in the Santee-Cooper Basin of South Carolina are significantly depressed relative to historical levels (USFWS et al. 2001).
GULF OF MEXICO DRAINAGES (EXCLUDING MISSISSIPPI RIVER BASIN)
Currently, the American eel appears to be secure in Alabama (Boschung and Mayden 2004).
Data from rotenone surveys in Fall Line and Coastal Plain pools of the Tallapoosa River downstream of Thurlow Dam, Alabama, in the autumn of 1990, 1992, and 1997 show reduced numbers of eels in the more recent samples (e.g., no eels were found in the Coastal Plain samples in 1992 and 1997) (John Hornsby, Alabama Department of Conservation and Natural Resources). In all samples, American eels made up a small proportion (less than 1.5 percent) of the fish samples. Hornsby observed many eels in the lower Tallapoosa River during the late 1950s and early 1960s, including thousands of small eels climbing Thurlow Dam on two separate occasions. A crash in the river's population of migratory fishes, which may have included American eel, occurred around 1969-1970, when three Corps of Engineers navigation locks were under construction on the Alabama River downstream of Thurlow Dam.
In Mississippi, eel abundance varies from year to year (Ross 2001), but no clear trend has been identified.
The America eel is native to much of Texas, but dams now impede upstream migrations, and the species has been eliminated from most central and western areas of the state (Chilton 1997).
MISSISSIPPI RIVER BASIN
In Arkansas, eels are "especially abundant in the lower Arkansas River (Robison and Buchanan 1988). However, statewide eel populations have undergone a "drastic decline" due to the construction of dams on virtually all of the state's major rivers (Robison and Buchanan 1988).
High dams on the Osage and White rivers have eliminated eels from large areas of the Ozarks in Missouri (Pflieger 1997).
In Kansas, historical records indicate that eels were more widely distributed and abundant 100 years ago than they are now (Snow 1875, Cragin 1885, Graham 1885, Cross and Collins 1995, Haslouer et al. 2005). Today, obstructions in the lower Arkansas River and its tributaries in Oklahoma and Arkansas block eel movements such that eels no longer occur in southern Kansas (Cross and Collins 1995). In the Kansas River basin, American eels formerly penetrated at least as far as Rawlins County, but today dams block access to that area; recent collections (1987, 2005) indicate that eels do sometimes still occur in streams in northeastern and central Kansas (Cross and Collins 1995; Haslouer et al. 2005; Tom Mosher, pers. comm., 2005).
Smith (1979) stated that the construction of dams has undoubtedly decreased the number of eels in Illinois. Available records mapped by Smith suggest that eels were never very common there. A map of collection sites in Illinois produced by the Illinois Natural History Survey indicates 16 eel collection sites before 1979 and none after 1979 ().
The American eel is not abundant in its Iowa range, but Harlan et al. (1987) stated that it did not appear to be on the decline over the last 20 to 30 years.
Anecdotal evidence suggests that eel numbers may have declined in Indiana since the 1970s and 1980s (Brant Fisher, pers. comm., 2005). Surveys by the Indiana Division of Fish and Wildlife in the White River and Blue River systems in southern and central Indiana also suggest a declining trend (Bob Ball, pers. comm., 2005). However, in all cases, this information is based on very small numbers of eels (fewer than 7 in any single year), so trend determination is problematic.
Coker (1930) reported that catches in the Mississippi River in Wisconsin and Minnesota were never significant and that the eel had been steadily disappearing from the whole basin for at least 30 years.
The Upper Mississippi River Long Term Research Monitoring Program has conducted annual standardized fish sampling in four upper Mississippi River pools (in Minnesota, Wisconsin, Iowa, and Illinois), an open river reach below St. Louis (Cape Girardeau, Missouri), and one reach of the Illinois River (La Grange Pool, Havana, IL) since the late 1980s (). Frequency of occurrence (percentage of samples containing at least one eel) was as follows: Pool 4, 1994 and 1996 (1% frequency of occurrence); Cape Girardeau: 4% in 1993, 2% in 1998, and 1% in the other years). In pools 8, 13, 26 and at Havana, frequency of occurrence of American eel (apparently rounded to two decimal places) was 0.00% in all years. Overall, it appears that eels were rarely or infrequently captured in all areas throughout the sampling period. Eels captures did not appear to decrease in frequency with any particular geographic pattern (e.g., south to north). However, reductions in sampling frequency and gear types used since 1990 (as well as small sample size) make trend analysis difficult. Similarly, statewide population trends in Wisconsin are uncertain (Lyons et al. 2000).
Mettee et al. (1996) reported that recent records of eels in the Tennessee River of Alabama are rare (these few records apparently are the only ones for the Tennessee River in Alabama). Despite widespread distribution in the Mobile basin, the inland distribution of American eels may have declined in recent years because few if any eels are able to traverse high-lift locks and dams; angler reports and sampling efforts indicate a progressive decline in abundance with each upstream dam (Mettee et al. 1996).
WEST INDIES/CARIBBEAN REGION
Anecdotal information and some limited river and estuarine sampling suggests that American eels are quite scarce in Puerto Rico and that over the past 20-25 years their abundance appears to have substantially decreased (Craig G. Lilyestrom, pers. comm., 2005).
Sources and Credits
- (c) Clinton & Charles Robertson, some rights reserved (CC BY), https://www.flickr.com/photos/dad_and_clint/4015394951/
- Adapted by rkkessler from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Anguilla_rostrata
- (c) FishBase, some rights reserved (CC BY-NC), http://eol.org/data_objects/20840786
- (c) FishBase, some rights reserved (CC BY-NC), http://eol.org/data_objects/20840788
- (c) WoRMS for SMEBD, some rights reserved (CC BY), http://eol.org/data_objects/32027652
- (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31377350
- (c) FishBase, some rights reserved (CC BY-NC), http://eol.org/data_objects/20840791
- (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31377351
- (c) NatureServe, some rights reserved (CC BY-NC), http://eol.org/data_objects/28813032
