American Eel Fecundity and Ovary Maturation in Relation to Body Size and Geographic Distribution

Abstract

AbstractFecundity, in relation to body length and weight, of migrating, sexually maturing female American Eels Anguilla rostrata differed significantly among sites between the upper St. Lawrence River (USLR) and south to Chesapeake Bay along the Atlantic coast of North America. Fecundity–size relations from two of four American Eel studies may be underestimated, affecting the interpretation of fecundity relations with size and distance from the spawning area and between Atlantic anguillid species. Body condition and ovary condition varied widely within and among sites. Condition at continental departure may have no geographic trend. The declines in condition during downstream migration within the St. Lawrence River and with increasing distance from the spawning area along the Atlantic coast may be statistical artifacts. Ovary condition increased for eels migrating downstream between the USLR and its middle estuary but showed no geographic trend at estuarine and coastal departure. Decreased relative fecundity with increasing size implies that the loss of large, fecund females from areas such as the USLR may have less of an effect on population fecundity than previously hypothesized but may be important for genetic and other reasons. Increased size and tissue lipid levels and decreased relative fecundity may be traits that aid American Eels migrating longer distances to spawn successfully. American Eels depart freshwaters with a higher fecundity and gonad development and lower tissue lipid levels and ova diameters than do similarly sized European Eels A. anguilla. Standardized methods and adequate sample sizes are needed to enhance the comparability and interpretation of fecundity studies. A better understanding of the relations among geographic differences in eel size, reproductive traits, and abundance is essential to effectively manage the American Eel population.