Eels at the Edge: Science, Status, and Conservation Concerns

Age, Growth, Mortality, and Sex Ratio of American Eels in Maryland’s Chesapeake Bay

Julie A. Weeder and Stephen D. Hammond


Abstract.—We examined the demography of American eels Anguilla rostrata at seven Maryland sites, including six Chesapeake Bay estuaries and one bay adjacent to the Atlantic Ocean. Eels caught by baited pots in estuaries tended to be young and small with rapid growth rates. Large eels were a higher proportion of catch in the Atlantic bay, where exploitation started only recently, than in heavily fished Chesapeake estuaries. Histological examinations indicated that all eels longer than 40 cm were female, but smaller eels were female, male, or undifferentiated in roughly equal proportions. Some eels were captured in commercial fishing gear after only one year in continental waters. Total mortality (Z), including postspawning mortality of emigrants, was estimated from catch curve analysis, giving a range of 0.62 to 1.44. Instantaneous natural mortality (M) was calculated as 0.25, from 3/maximum age (12). Instantaneous fishing mortality, ZM, ranged from 0.37 to 1.19 and, in one case, only five age classes were observed. We considered the impact of latitude, habitat productivity, density, sex ratio, and fishing on eel populations. We postulate that heavy fishing pressure reduced the density and modal size of eels in surveyed estuaries. Changes in management policy to reduce fishing mortality and increase spawning emigration are recommended.