History of Fisheries Management in the Upper Henry's Fork Watershed

Abstract

During the 1970s, the rainbow trout (Oncorhynchus mykiss) fishery of the Henry's Fork of the Snake River was widely regarded as the finest in the nation. However, rainbow trout abundance in the Box Canyon reach declined 80 percent between 1978 and 1991. Rainbow and cutthroat-rainbow hybrid trout are the most popular sport fish in the watershed, but the only native trout is the Yellowstone cutthroat trout (Oncorhynchus clarki bouvieri). Prior to habitat alteration, Yellowstone cutthroat trout thrived in the watershed most likely because of life history traits that allowed optimal use of different types of lake, river and small stream habitat in an aquatic system generally lacking in soluble nutrients. Construction of Henry's Lake and Island Park dams in 1923 and 1938, respectively, created productive reservoir fisheries but greatly restricted the ability of trout to migrate throughout the watershed. Extensive stocking of hatchery rainbow trout and chemical treatments of Island Park Reservoir and the river in 1958 and 1966 essentially eliminated Yellowstone cutthroat trout from the upper watershed except in Henry's Lake. Fisheries throughout the upper watershed were supported by stocking of hatchery rainbow and hybrid trout from the 1920s until the late 1970s. Loss of hatchery supplementation after 1977 in the wild trout management reach downstream of Island Park Dam was inadvertently mitigated by introduction of large numbers of reservoir fish during drawdowns of Island Park Reservoir in 1977, 1979, 1981 and 1984. Introduction of reservoir fish into the river during the 1992 drawdown reversed the population decline of the late 1980s; however, the population declined in subsequent years. The 1979 and 1992 drawdowns were conducted to facilitate chemical treatment of the reservoir to remove Utah chubs (Gila atraria), which along with habitat degradation, have contributed to declines in wild trout Jlbundance and return-to-creel rates of hatchery fish in the reservoir and its tributaries. Current management strategies in the upper Henry's Fork watershed include: 1) cooperatively managing winter flows from Island Park Dam to optimize trout recruitment under constraints imposed by irrigation rights and hydroelectric power needs, 2) restoring connectivity and habitat on tributaries to Henry's Lake and Island Park Reservoir, and 3) restoring wild Yellowstone cutthroat trout in the Henry's Lake system.