Yellowstone Cutthroat Trout Management on the South Fork Snake River

The Idaho Department of Fish and Game (IDFG) altered fishery management efforts and focus on the South Fork in 2004 to better conserve ant protect YCT. These new management efforts included working closely with the Bureau of Reclamation (Reclamation) to benefit YCT conservation, and the effectiveness of management efforts were evaluated primarily with fish recruitment data collected from two monitoring sites sampled each fall. Management efforts could be described as being three-pronged. The first prong dealt with spawning tributaries and involved using fish traps on the four main tributaries to remove Rainbow Trout and hybrids from spawning runs. Rainbow Trout and Rainbow x Cutthroat trout hybrids (hereafter collectively referred to as RBT) are identified as the biggest threat to the continued persistence of YCT in the South Fork because of risks through competition and hybridization. The second management prong dealt with flow manipulation. Previous research had indicated flows similar to a natural (unregulated) hydrograph in both timing and shape, benefitted YCT recruitment while limiting recruitment of RBT. The third management prong involved increasing angler harvest of RBT. All three management prongs were designed to achieve the same goal, which was the preservation of the genetic integrity of YCT in the South Fork and the population’s long-term viability.

IDFG is requesting the continuation of assistance to study the increase of the ratio of YCT to Rainbow Trout in the South Fork by continuing to operate tributary weirs during spring spawning runs and managing spring flows to mimic the timing and magnitude of a natural hydrograph.