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

Reproductive Strategy of Female American Eels Among Five Subpopulations in the St. Lawrence River Watershed

Valérie Tremblay


Abstract.—The American eel Anguilla rostrata is declining in the St. Lawrence River watershed, where sex ratio is highly unbalanced in favor of females. Since the American eel is a panmictic species, this demographic dominance is implicated in reproductive potential of the species. The major objective of this study was to evaluate the reproductive strategies of five subpopulations of female eels. It was assumed that fecundity varies among subpopulations according to their migration distance because of the tradeoff between energy allocated to gonads and to somatic tissues. Thirty female silver eels were collected from each of five locations in the St. Lawrence watershed 2,850–4,300 km from the spawning area. Among subpopulations, mean length ranged from 67.9 to 104.3 cm, weight from 595 to 2,366 g, fecundity from 6.5 to 14.5 million oocytes, age from 20 to 23 years, gonadosomatic index from 2.9 to 4.1%, and somatic lipid content from 17.5 to 21.7%. Because of panmixia, no genetic influence on intersite variability is expected. Environmental differences in growth habitats and individual fitness might determine acquisition and allocation of resources, as well as subsequent variability in traits that would affect reproduction. In contrast to previous hypotheses, variations in such traits were attributed to eel size rather than migration distance. The number of oocytes per silver eel was positively correlated with length rather than negatively correlated with migration distance. In the St. Lawrence watershed, large eels are highly fecund regardless of their distance from the spawning ground.