Minimum stream length requirements for McCloud River redband trout (Oncorhynchus mykiss spp) in Trout and Tate creeks, Siskiyou County, California

I located existing and potential barriers to fish movement, evaluated habitat, and estimated minimum stream lengths required to maintain genetically viable populations of McCloud River redband trout (Oncorhynchus mykiss spp) in two streams, Trout and Tate creeks, in the upper McCloud River basin in northern California. The goal of this research was to evaluate the potential effectiveness of isolation management to protect and restore populations of redband ttout. Minimum stream length requirements were based on reach-scale estimates of fish density and survival. Population estimates were obtained using a modification of the Hankin and Reeves (1988) approach and from spotlight surveys. Redband trout were the only salmonid species observed in Trout Creek while Tate Creek contained redband trout and brook trout (Salvelinus fontinalis). Redband trout densities in summer 2009 were approximately 378 km-1 and 652 km-1 in Trout and Tate creeks, respectively. Estimates of minimum stream length needed to maintain a population of 2,500 individuals with densities observed in 2009 ranged from 7.35 to 13.23 km on Trout Creek and from 4.26 to 7.67 km on Tate Creek. Abundance differences in streams were probably due to availability of warm, retentive, high productivity habitat in the lower reaches of the larger Tate Creek watershed. Trout Creek was determined to be a poor candidate for deliberate isolation because a percolation barrier isolates it from the upper McCloud River and further barriers would fragment already limited habitat. Although trout from the lower reach of Tate Creek showed morphological evidence of hybridization, the stream supported a higher trout density and available habitat exceeded estimated minimum stream length. As such, it may represent a viable isolation candidate, with sufficient resources to support growth of translocated populations with greater genetic purity. Existing culverts on both streams do not appear to significantly fragment habitat.