Seasonal Patterns in Growth Diet, and Prey Availability of Brown Trout in Groundwater-Dominated Streams

Mechanisms governing growth of stream-dwelling Brown Trout Salmo trutta during the typical growing season (spring through autumn) have been frequently studied; however, relatively little is known about these systems during winter. Groundwater-dominated streams may maintain relatively warm winter temperatures, which may increase the availability of potential prey and create favorable foraging conditions for trout. We examined seasonal diet and growth of Brown Trout, and prey availability, across six streams in the Driftless Ecoregion of Southeastern Minnesota across three years. Brown Trout were sampled up to three times per winter and summer, PIT tagged for identification, and diet samples taken with gastric lavage. Benthic and drift samples were collected on each sampling event to estimate prey composition and abundance. Individual growth of recaptured fish was calculated at the end of each season. Our analyses suggest that seasonal trout growth is influenced by the composition of diet contents.  These results will inform management of groundwater-dominated streams by revealing both temporal trends in growth and information related to prey communities and prey selectivity on a seasonal basis.