The idiosyncrasies of streams: local variability mitigates vulnerability of trout to changing conditions

Abstract

Land use and climate change are two key factors with the potential to affect stream conditions and fish habitat. Since the 1950s, Washington and Oregon have required forest practices designed to mitigate the effects of timber harvest on streams and fish. Yet questions remain about the extent to which these practices are effective. Add in the effects of climate change—lower summer flow and warmer water temperatures in some streams— and more questions arise. Scientists with the multipartner Trask Watershed Study set out to learn more about how the effects of climate change and timber harvests may interact and affect the long-term survival of cutthroat trout populations in the Oregon Coast Range. They collected data from four streams before and after an adjacent timber harvest and used that information to model stream and trout responses to these changing conditions. They also conducted experiments in semi-natural streams to evaluate the relationship of bird predation and instream cover to trout survival. The scientists found that local variability in stream habitat, such as water depth and instream cover, play a greater role in reducing the effects of timber harvest and climate change on trout than previously realized. Instream cover and shade improve trout survival by providing a place to hide from predators.

Citation

Watts, Andrea; Penaluna, Brooke; Dunham, Jason. 2016. The idiosyncrasies of streams: local variability mitigates vulnerability of trout to changing conditions. Science Findings 191. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 5 p.