Drifting Invertebrates, Stomach Contents, and Body Conditions of Juvenile Rainbow Trout from Fall through Winter in a Wyoming Tailwater

We investigated the availability of drifting invertebrates and the stomach contents and body conditions of stocked (hatchery) and naturally spawned (wild) juvenile (20–25 cm total length) rainbow trout from fall through winter in the Big Horn River downstream from Boysen Dam in Wyoming. When the density and biomass of drifting invertebrates declined with water temperature during the fall, stomach contents and body conditions substantially decreased among both wild and stocked fish. During the coldest portion of the winter, the density of small drifting invertebrates increased as did the body conditions of both wild and hatchery trout. We suggest that the perceived increase in body conditions during late winter was due to survival of fish with higher body conditions and not growth of fish from fall to late winter.