Idaho Department of Fish and Game Grant for Yellowstone Cutthroat Trout Management

Yellowstone Cutthroat Trout (YCT) are the native trout of the South Fork Snake River (South Fork). The river supports the strongest remaining fluvial population within their historical range in Idaho. Across most of the species range, YCT have experienced reductions in abundance and distribution. In August 1998, conservation groups petitioned the United States Fish and Wildlife Service (USFWS) to list YCT under the Endangered Species Act (ESA). In February 2001, the listing petition was denied, and conservation groups filed a lawsuit in January 2004 which led to a 12-month review of the status of YCT. The USFWS determined that YCT did not warrant listing under the ESA in February 2006. However, YCT have continued to sustain declines in their abundance and distribution across their historical range. 

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.

With Reclamation’s financial assistance, management efforts have been documented to benefit YCT in the South Fork. The South Fork YCT population is the strongest Cutthroat Trout population in Idaho with all life history strategies still present. With other YCT within the species native range struggling or continuing to face significant threats to their continued persistence, the South Fork population will likely play a key role in future ESA listing petitions.

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.