Regional variation and the effect of lake: river area on sex distribution of American eels

Silver phase American eels. Anguilla rostrata. were collected while migrati ng from five rivers in Maine, U.S.A. Sex ratios varied from 49 to 98% male for these rivers and had a range of 46% over a 30 km distance between the m ouths of three rivers. The proportion of male eels was inversely related to the amount of lacustrins habitat in the five drainage areas (r = -0.95. P = 0.014). A combination of these sex ratios and published data from two Nov a Scotia rivers showed large variation in the proportion of male eels withi n 1 degrees of latitude. Thus the hypothesis from the literature that the d istribution of the sexes is dependent upon distance of larval transport was not supported. Eels migrating from lacustrine habitats within a river were predominately female. while eels migrating from fluvial habitats were pred ominately male, regardless of upstream distance. Apparently river habitat i nfluences the distribution of the sexes and may play a role in sex determin ation. (C) 2001 The Fisheries Society of the British Isles.