Winter Fisheries Research and Habitat Improvements on the Henry's Fork of the Snake River

Abstract

The rainbow trout (Oncorhynchus mykiss) population in the Henry's Fork of the Snake River from Island Park Dam to Riverside Campground is limited by reauitment of juveniles, with the bottleneck occurring during their first winter. Loss of juvenile trout from this area is appreciable-an estimated 188,000 individuals during some years. Fish loss during early winter is related to insufficient habitat that decreases suroival and increases emigration. Loss of juvenile trout during late winter is related to loss of macrophyte habitat and low late-winter discharge. During late winter, emigration probably causes much of the lass. Some movement successfully occurs between Last Chance and Box Canyon and between all river sections and PinehavenRiverside. However, most of the loss remains unexplained. Habitat improvement projects developed to decrease loss of juvenile trout through this critical winter period have been largely unsuccessful, primarily because of sediment deposition in the structures. One exception may be the installation of a fish passage structure on the Buffalo River that allows spawning rainbow trout from the Henry's Fork to access the spring-influenced Buffalo River, thus giving juveniles the opportunity to spend the winter in warmer water, where woody debris provides habitat throughout the winter.