Facultative catadromy in American eels: testing the conditional strategy hypothesis

摘要

Analyses of otolith strontium:calcium (Sr:Ca) ratios in 162 American eels Anguilla rostrata of the St. Jean River watershed in eastern Canada demonstrated the co-existence of 6 migratory patterns, including freshwater and brackish water residence, and the predominance of an amphidromous migratory behavior. We tested the hypothesis that the choice of a particular life-history tactic may be controlled by a conditional strategy with status-dependent selection. This prediction was not supported because migratory patterns did not vary as a function of individual size, age and/or sex of eels prior to migration. However, we demonstrated that the utilisation of the estuarine brackish environment, more productive than the freshwater river and lake, resulted in a higher growth rate. Freshwater yellow eels, the typical catadromous tactic, were rare and experienced lower growth rates. Moreover, we suggest that freshwater overwintering periods are not recorded in otoliths owing to the cold winter climate that occurs at northern latitudes. Thus, Sr:Ca ratio patterns that show brackish residence may in some cases hide a seasonal migration between fresh and brackish habitats.