Comparison of Reproductive Characteristics of Stocked and Naturally Occurring American Eels

The discovery of smaller and younger downstream migrating female American eels in the St Lawrence River (SLR) resulting from the stocking of glass eels has raised questions about the ecological impact of stocking.  In this study we made comparisons of reproductive life history traits (age, total length, body composition, energy density (kJ/g bw), and parental investment (proximate composition of ovulated eggs) of female silver eels collected while migrating from rivers in Massachusetts, Nova Scotia and the SLR (both stocked and non-stocked).  Age, total length, and total energy (kJ) were greater in naturally occurring St Lawrence eels.  Energy density (kJ/g bw) was greatest in the stocked eels and parental energy investment in the eggs was similar for all eels.  Age and length of stocked eels were similar to eels from Nova Scotia and Massachusetts locations and to other locations in the species range with similar habitat conditions.  We hypothesize that transplanting eels to the upper SLR system creates localized habitats that are similar to densely populated coastal river systems and the resulting female traits are consistent with this scenario.