Anguilla rostrata (Lesueur, 1817)
Basis for Listing
The historical distribution of the American Eel (Anguilla rostrata) in Minnesota was likely restricted to the Mississippi (downstream of St. Anthony Falls), the Minnesota, and the St. Croix rivers. However, since the construction of the lower and upper St. Anthony locks for commercial navigation, occurrences in the Mississippi upstream to St. Cloud have been confirmed from angler and newspaper photographs, which include a former DNR state record caught in the Crow River. The occurrences of American Eels in the Lake Superior drainage (i.e., Duluth-Superior Harbor and Blackhoof and Knife rivers) likely followed the construction of the Welland Canal that bypasses Niagara Falls or the Chicago Sanitary and Ship Canal that connects the Mississippi Drainage to the Great Lakes (Phillips, in preparation).
Although survey and angling effort is not uniform through time, records of the American Eel from Minnesota waters have drastically declined since 2000. From 1971-1980, there are 35 records, 1981-1990 (25), 1991-2000 (39) and 2001-2012 (13) (Phillips, in preparation). There are similar reports of decline across the species’ range in North America. In 2007, the U.S. Fish and Wildlife Service (USFWS) and National Marine Fisheries Service completed a review of the American Eel for protection under the federal Endangered Species Act. However, the review concluded that federal listing was not warranted at that time. Another petition to review the species was submitted in 2010 (USFWS 2011). The Committee on the Status of Endangered Wildlife in Canada listed the species threatened in 2012. The recent and dramatic global and regional declines prompted listing the American Eel a special concern species in Minnesota in 2013.
The American Eel has a long flexible and snake-like body that is dark brown to olive, with a cream or white belly. Scales are small and inconspicuous. There are paired pectoral (side) fins behind the head; the low and long many-rayed dorsal fin begins about one-third the way down the back and is continuous with the caudal and anal fins. The mouth has jaws with teeth, and the gill opening is a single small slit. The species is often confused with members of the lamprey family (Petromyzontidae), which has the following distinguishing characters: mouth in adults is a sucking disk and in juveniles (ammocoetes) a hood, void of eyes. Body scales and pectoral fins are absent, no rays in dorsal fin. Gills have seven circular openings (Lyons et al. 2006). The largest American Eel reported from Minnesota waters was 1.05 m (3.44 ft.) total length (LTRMP 2013).
In Minnesota, preferred habitats of the American Eel include moderate-sized or large rivers having continuous flow and a mud or rock bottom that provides daytime cover (e.g., boulders and log jams). The species will also utilize lower reaches of tributaries to large rivers (Phillips, in preparation). In the Mississippi River (Pool 4) from 1990-2002, American Eels were collected in the following habitats (and frequency): backwaters (10 times), tailwater zones of dams (10), main channel borders (8), and side channel borders (2) at depths ranging from 0.8-3.1 m (2.6-10.2 ft.) (LTRMP 2013).
Biology / Life History
The American Eel has a very complex life cycle. It is a catadromus species, meaning it migrates from freshwater to saltwater to spawn. In Minnesota, the population is comprised entirely of females, while most males spend their lives in streams along the Gulf of Mexico and Atlantic Coast. The estimated age of sexual maturity for females is 10-20 years or older (Haro 2014); northern populations generally mature later and grow larger. Females average 91.4 cm (36 in.) total length. Males mature sooner than females and reach a maximum of 50.8 cm (20 in.). The species is assumed to spawn in the Sargasso Sea and then die. When the eggs hatch, they transform into leptocephalus (flat and transparent) larvae that ride ocean currents, such as the Gulf Stream along North America’s Atlantic Coast. However, larvae destined for Minnesota ride currents into the Gulf of Mexico. At about one-year, the leptocephalus larvae mature into "glass eels", some of which will ascend the Mississippi River. When they reach the mouths of coastal streams during their migration back to fresh water, they are called “elvers”. The yellow phase of the American Eel lasts from 5-20 years, and the life cycle completes as they migrate downstream to spawn (Phillips, in preparation), at which time they are called "silvers".
Conservation / Management
Various causes have been cited for the decline of the American Eel in North America, including dams, commercial harvest, parasites, pollution, the bioaccumulation of PCBs, and hydro-power development. Therefore, limiting commercial harvest, habitat protection, control of contaminants, and removal or mitigation of migratory barriers (Haro 2014) would all benefit the species. That said, the recent and precipitous decline may be attributed to climatic change that may be detrimental to the leptocephalus larval stage of the species life cycle. Warming ocean temperatures have reduced the mixing of different depths and nutrients and altered currents. This may have decreased the food supply of the larvae and increased their migration period to coastal streams (Phillips, in preparation).
Conservation Efforts in Minnesota
The American Eel presents an unusual situation in Minnesota, since there are no breeding populations. Data has been collected on the species and its habitat by the MN DNR Long-term Resource Monitoring Program (LTRMP) and State Wildlife Grant Program surveys. The recent inception of the Clean Water Legacy Program in Minnesota will also yield dividends to the water quality of streams where the species occurs.
References and Additional Information
Becker, G. C. 1983. The fishes of Wisconsin. University of Wisconsin Press, Madison, Wisconsin. 1052 pp.
Haro, A. 2014. Anguillidae: Freshwater Eels. Pages 313-331 in M. L. Warren, Jr. and B. M. Burr, editors. Freshwater Fishes of North America. Volume 1. Johns Hopkins University Press, Baltimore, Maryland.
Ickes, B. S., M. C. Bowler, A. D. Bartels, D. J. Kirby, S. DeLain, J. H. Chick, V. A. Barko, K. S. Irons, and M. A. Pegg. 2005. Multiyear synthesis of the fish component from 1993 to 2002 for the Long Term Resource Monitoring Proqram. U.S. Geological Survey, Upper Midwest Environmental Sciences Center, La Crosse, Wisconsin. LTRMP 2005- T005. 60 pp. + CD-ROM (Appendixes A-E)
Long Term Reasource Monitoring Program (LTRMP). 2013. Mississippi River pools 4 and 8 fish survey data (1989-2015). LTRMP Fisheries Data, Graphical Fish Database Browser [web application]. Upper Midwest Environmental Sciences Center, USGS, La Crosse, Wisconsin. <http://www.umesc.usgs.gov/data_library/fisheries/graphical/fish_front.html>. Accessed 11 April 2013.
Lyons, J., P. C. Hanson, E. A. White. 2006. A photo-based computer system for identifying Wisconsin fishes. Fisheries 31(6):269-275.
MacGregor, R., J. M. Casselman, W. A. Allen, T. Haxton, J. M. Dettmers, A. Mathers, S. LaPan, T. C. Pratt, P. Thompson, M. Stanfield, L. Marcogliese, and J. D. Dutil. 2009. Natural heritage, anthropogenic impacts, and biopolitical issues related to the status and sustainable management of American Eel: a retrospective analysis and management perspective at the population level. American Fisheries Society Symposium 69:713-740.
NatureServe. 2009. NatureServe Explorer: an online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington Virginia. <http://www.natureserve.org/explorer>. Accessed 26 May 2009.
NatureServe. 2013. NatureServe Explorer: an online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington Virginia. <http://www.natureserve.org/explorer>. Accessed 30 March 2013.
Ogden, J. C. 1970. Relative abundance, food habits, and age of the American Eel, Anguilla rostrata (LeSueur), in certain New Jersey streams. Transactions of the American Fisheries Society 99:54?59.
Phelps, Q. E., J. W. Ridings, and D. P. Herzog. 2014. American Eel population characteristics in the Upper Mississippi River. American Midland Naturalist 171(1):165-171.
Phillips, G, L. American Eel Anguilla rostrata (Lesueur, 1817). In J. T. Hatch, G. L. Phillips, K. P. Schmidt, and M. McInerny, editors. The Fishes of Minnesota (in preparation).
Phillips, G. L., and P. A. Cochran. American Eel Anguilla rostrata (Lesueur). In J. T. Hatch, G. L. Phillips, K. P. Schmidt, M. C. McInerny, and J. C. Underhill, editors. The Fishes of Minnesota (in preparation).
USFWS. 2011. U. S. Fish & Wildlife Service, northeast region [web page]. <http://www.fws.gov/northeast/newsroom/eels.html>. Accessed 30 March 2013.