Factors Influencing Winter Growth and Condition of Brown Trout in Groundwater Dominated Streams of the Driftless Ecoregion

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 may maintain relatively warm winter temperatures, which can increase the availability of potential prey and create more favorable growth and foraging conditions for trout.  We examined winter diets, growth, and body condition of Brown Trout across 35 streams in the Driftless Ecoregion of Southeastern Minnesota.  Brown Trout were sampled up to three times per winter, PIT tagged for identification, and diet samples were taken via gastric lavage.  Individual growth was measured at the end of winter for recaptured trout.   We used multiple regression modeling to examine the relationships between dietary and environmental variables and Brown Trout growth and condition.  The degree to which a stream was thermally buffered by groundwater showed a significant positive relationship with trout growth and condition.  Additionally, total consumption and diet composition variables also affected trout growth.