Distribution and Status of Yellowstone Cutthroat Trout in the Henry's Fork Watershed

Abstract

We electrofished and snorkeled streams in the Henry's Fork watershed upstream of and including Fall River, the Teton River watershed, and the Snake River Plain Sinks drainages adjacent to the western edge of the Henry's Fork watershed to assess the distribution of Yellowstone cutthroat trout (Oncorhynchus darki bouvieri). Yellowstone cutthroat trout were present in 20 of 138 reaches of stream sampled in the Henry's Fork watershed. They were isolated from nonnative salmonids in all or part of eight of the 20 reaches. This represents occupancy in about 17 percent of the historic range of the subspecies and exclusive occupancy in about 3 percent thereof. Yellowstone cutthroat trout were d,served in 35 of 48 streams sampled in the Teton watershed and were the only trout species observed in five of these 35 streams, representing occupancy in about 89 percent of fish-bearing habitat and exclusive occupancy in about 19 percent offi sh-bearing habitat, all of which lies within the historic range of the subspecies. In the Sinks drainages, Yellowstone cutthroat trout were observed in 19 of the 38 streams surveyed and were the only trout species observed in seven. They occupied about 52 percent offis h-bearing habitat and exclusively occupied about 19 percent of it. We do not know with certainty whether the Sinks drainage streams lie within the historic range of Yellowstone cutthroat trout. Distribution of Yellowstone cutthroat trout within their historic range has drastically declined throughout the Henry's Fork watershed; however, additional populations have been established outside of the subspecies' historic range. The status of Yellowstone cutthroat trout within its current range is uncertain because of the lack of genetic information and the presence of nonnative salmonids.