Research Document - 2013/134
Recovery Potential Assessment for the American Eel (Anguilla rostrata) for eastern Canada: life history, distribution, reported landings, status indicators, and demographic parameters
By D.K. Cairns, G. Chaput, L.A. Poirier, T.S. Avery, M. Castonguay, A. Mathers, J.M. Casselman, R.G. Bradford, T. Pratt, G. Verreault, K. Clarke, G. Veinott, and L. Bernatchez
Abstract
This report assembles biological, fisheries, and abundance indices data for the American Eel (Anguilla rostrata) Recovery Potential Assessment, which was held in Ottawa in June 2013. Data are compiled by four zones which are primarily or entirely in Canada (St. Lawrence Basin, Northern Gulf of St. Lawrence and Newfoundland, Southern Gulf of St. Lawrence, Scotia-Fundy) and three zones which are primarily or entirely in the United States (Atlantic Seaboard North, Atlantic Seaboard Central, Atlantic Seaboard South). American eels are born in the Sargasso Sea, migrate as leptocephali towards continental waters, metamorphose to glass eels, elvers, and yellow eels, and then return to the Sargasso Sea as silver eels to spawn and die. American eels are panmictic, meaning that they are the progeny of parents which mix randomly on the spawning ground. Stock-recruitment dynamics of the American Eel are poorly understood. It is possible that shifts in the ocean ecosystem (non-stationarity) substantially influence the number of recruits produced by a given quantity of spawners.
Eels are present but rare in Greenland and Labrador. They are widespread and often common in coastal bay and estuarine waters, and in accessible fresh waters, of the east coast of North America from Newfoundland to Florida. Eel abundance in the Caribbean Basin and the Gulf of Mexico and associated drainages is poorly known but possibly substantial. On the basis of research and fishing records and a habitat classification scheme, it is estimated that the east coast of North America between the Strait of Belle Isle and the Florida Keys contains 23,270 km2 of brackish and salt water eel habitat. Freshwater aquatic habitat of the US Atlantic Seaboard (17,763 km2) exceeds brackish and salt water eel habitat (14,360 km2), but an unknown proportion of fresh water habitat is inaccessible to eels. Reported range-wide eel landings peaked in the late 1970s at ca. 3,000 t per year and have since declined to ca. 750 t per year. General Linear Modeling (GLM) indicates a severe (>99%) decline in eel recruitment to and standing stock of Lake Ontario over two or more generations (32 years), and generally declining indices elsewhere in Canada. Trends over one generation (16 years) show an improvement relative to trends over two generations. Over one generation, standing stock indices have declined in three of four zones, but neutral and rising trends are also found. US east coast abundance trends reported in a recent US assessment varied by analytic method from no temporal trend to significant downward trends.
American Eel demographic parameters from eastern North America were examined for systematic geographic variation. Elver lengths increase with latitude and distance from the spawning ground. Trends in yellow eel growth rates and size and age of silver eels showed differing trends for areas south of Cabot Strait versus those north and west of Cabot Strait. Silver eel length varied little with latitude south of Cabot Strait, but was greatest at the maximum distance from the spawning ground, in the St. Lawrence Basin. Percent male was lowest in northern areas, but otherwise sex ratios did not vary consistently with latitude. Fecundity increases with female eel size, but published size to fecundity relationships show widely varying fecundity estimates for a given eel size. Natural mortality rate of the American Eel is poorly known. Equations derived from European eel data and based on body mass, water temperature, density, and sex, appear to be the best available method to estimate natural mortality of the American Eel. Proposed recovery objectives for the American Eel in Canada are increases in abundance indices in the short term (one generation), rebuilding of abundance to levels of the mid 1980s in the medium term (three generations), and maintenance of abundance in the healthy zone of a precautionary approach framework in the long term (>50 years).
- Date modified: