Dynamics of Resources of the American Eel, Anguilla rostrata: Declining Abundance in the 1990s

Abstract

Evidence indicates that prehistoric and early historic American eel resources were extremely abundant and heavily used in North America, particularly by the St. Lawrence Iroquois. Over the past 50 years, abundance, as indicated by catch, has fluctuated dramatically. From the mid-1980s throughout the 1990s, commercial catch has declined markedly across most of the North American range. Cacthes were approximately equal in Canada (52%) and the United States (48%), with trends generally similar, reaching record high levels in the 1970s and 1980s. In the United States, where fish are younger, catches declined in the 1980s and preceded Canadian declines by a decade, then levelled off and decreased in the late 1990s. Decreases in the past two decades were extreme and similar at both extremities of the range. In Canada, all provincial catches associated with the Gulf of St. Lawrence have showed a synchronous exponential decline. Declines have been most dramatic at the extremity of the northern range and have particularly affected the St. Lawrence River-Lake Ontario stock, suggesting evidence of a general decline of this panmictic species and reflecting inadequate recruitment to maintain distant stocks. Scientific indices confirm the overall decline. The long-term eel ladder index indicates that recruitment to the highly fecund SLR-LO stock has virtually ceased, having increasing and far-reaching ramifications on the overall reproductive potential of the species. Recruitment indices are synchronous with catch and resources declines, most obvious in the SLR-LO stock. Declines no doubt are a combination of multiple factors. The cumulative effect of intensively fishing the various life stages of this slow-growing , late-maturing fish must be important. Changes and loss of habitat through dam construction have been extensive. Habitat and food web changes associated with exotic species such as alewife and dreissenids affect eel behaviour and distribution. Oceanic factors and changes may also be involved. Recruitment to the SLR-LO stock with appropriate lags is highly significantly correlated with the North Atlantic Oscillation Index. A joint management goal should be to reduce human-induced mortality and increase escapement, and short-term stocking of the upper SLR-LO ecosystem should be considered.