Diet patterns differ between naturally- and hatchery-produced lake trout across life stages

Abstract

Hatchery-reared fish often have behaviors suited for hatchery conditions and can maintain those behaviors after being stocked in natural environments. Diet-related behaviors that differ between stocked and wild fish can include feeding patterns and prey selection. Most comparisons of stocked and wild fish diets have evaluated patterns for short periods (<1 year) after stocking or focused on juvenile behaviors. Here, we tested the hypothesis that hatchery rearing has lifetime effects on foraging success and diet composition by comparing diet patterns between stocked and wild lake trout (Salvelinus namaycush) in Lake Champlain across sizes that include juveniles and adults. Lake trout foraging success was assessed using lipid content and stomach content analyses, including frequency of empty stomachs, stomach fullness by count, and reconstructed mass of prey fish consumed. Diet composition was evaluated using frequency of occurrence for each prey item and fatty acid profiles. Stocked lake trout consumed significantly fewer prey fish by count (27 % average modeled reduction) and had significantly lower lipid content (21 % average modeled reduction) compared to wild fish across all sizes. Stocked fish also tended to have empty stomachs more frequently (19 % average modeled increase) and lower reconstructed mass of prey fish consumed (25 % average modeled reduction) compared to wild fish. Diet composition was similar, however, between stocked and wild fish with most lake trout primarily consuming alewife (Alosa pseudoharengus). Together, these results suggest that the population of stocked lake trout (juveniles and adults) had lower foraging success and energy consumption compared to wild fish.