Assessment of Fat Reserves Adequacy in the First Migrant Silver American Eels of a Large-Scale Stocking Experiment

Abstract

An experimental stocking program in the St. Lawrence River–Lake Ontario system provided a unique opportunity to compare reproductive fitness of migrant silver American Eels Anguilla rostrata from the stocking program (S_M) and wild migrants (W_M), both of which were grown in the same location. Body size, muscle lipid stores, oocyte development, and morphometric indices of silvering were compared between S_M and W_M eels captured in the St. Lawrence River estuary. Migrant eels from the stocking program were smaller than wild migrants from the estuary, but their size was similar to migrating wild silver American Eels from their site of original capture on the Atlantic coast of New Brunswick and Nova Scotia. A bioenergetic model was used to estimate the costs of migration and reproduction and the duration of migration_. The adequacy of the measured lipid reserves to meet these estimated energetic costs was assessed for S_M and W_M eels. Gonad maturation and stage of silvering for S_M eels were less advanced than that for W_M eels, and they had lower initial muscle fat reserves and higher estimated energetic requirements for migration as a consequence of their smaller size. It was estimated that 100% of the S_M eels would not have adequate fat reserves for migration and reproduction, whereas 57% of the W_M eels would have adequate reserves. Smaller-sized S_M eels would take 1.6 times longer to reach the spawning grounds than W_M eels and, thus, may not arrive in synchrony with these wild migrants. Thus, smaller-sized, out-migrating, stocked eels from the upper St. Lawrence River are less likely than wild migrants to complete successfully their migration and reproduction. These results support the recommendation to source and stock American Eels at sites where they have similar life strategies to increase the likelihood of successful silver eel escapement.

Received November 27, 2013; accepted April 9, 2014

ACKNOWLEDGMENTS

This study is a corroborative project partially funded by Ontario Power Generation (OPG) as part of the OPG Action Plan for American Eel. Thanks are extended to A.-M. Pelletier and M. Tremblay for their work in the field and laboratory. M. Noël, H. Talbot, and S. Trottier are thanked for conducting lipid and water content analyses. M. Boudreau and F. Boily are thanked for histological evaluations. Y. Mailhot is acknowledged for his contribution to the study design. The collaboration of American Eel commercial fishers was essential for the success of this work. Thanks to C. Côté for her useful comments on this manuscript.