Differential lipid dynamics in stocked and wild juvenile lake trout

After more than 40 years of stocking, lake trout ( Salvelinus namaycush ) in Lake Champlain have started to exhibit strong, natural recruitment. The abrupt surge in recruitment suggests a change in limiting factors such as prey availability or overwinter survival. The distribution of juvenile wild lake trout varies in relative abundance among regions of Lake Champlain. The differences suggest the prey base, or foraging success, may vary geographically within the lake. Stocked and wild lake trout may differ in their ability to use resources and in overwinter survival. One metric that can indicate differences in resources across regions is lake trout lipid content, which reflects the quality of available food and serves as an important energy reserve for overwinter survival. We quantified total lipid content of stocked and wild juvenile lake trout across spatial (lake regions) and temporal (seasonal) scales. No spatial differences in lipid content were apparent. Wild fish had greater lipid content than stocked fish. Seasonally, stocked fish showed a continuous drop in lipid content from pre-winter levels at stocking to the following autumn. Wild fish showed a cyclical summer increase in lipids following winter depletion, which plateaued by autumn. The high lipid content of hatchery lake trout may be necessary as they acclimate to foraging in the wild. Hatcheries would benefit from evaluating whether post-stocking survival could be improved by altering feeding or rearing regimes.