Response of Wild Rainbow (Salmo gairdneri) and Cutthroat Trout (S. clarki) to Stocked Rainbow Trout in Fertile and infertile Streams

Abstract

Wild rainbow trout (Salmo gairdneri) and cutthroat trout (S. clarki) were unaffected by stocking of catchable-size rainbow trout in two Idaho streams, except at the highest stocking rates, and even then the effects were limited. In the infertile stream, stocking 50 or 150 trout per section (doubling or tripling the density) did not reduce the abundance of wild cutthroat trout. Wild trout abundance declined at a faster rate in an unreplicated section stocked with 500 trout than in unstocked sections. In the fertile stream, stocking 50 or 100 hatchery trout in sections containing 26–120 similar-sized wild trout did not increase the dispersion or reduce the abundance, growth, or survival rates of wild rainbow trout. When we stocked 400 trout (100 on four dates) in sections containing 32–53 tagged wild trout of similar size, the summer mortality rate of wild trout was higher in stocked than in unstocked sections; the other parameters were not significantly different.