Fish Assemblage Models for Alternative Futures
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The ability to forecast future distributions of freshwater fish species is a pressing management need, but is complicated by climate change, invasive aquatic species, and on-going human demands for water and other natural resources. Paired climate-hydrological models suggest a warmer and more hydrologically variable environment for many streams and rivers. Shifts in distributions of native species are already detectable. At the same time, efforts are underway in many watersheds to slow or mitigate adverse changes to aquatic ecosystems, even as human pressures on water and land resources increase. We discuss a spatially-structured fish assemblage modeling framework that we are using to explore linkages between environmental change and fish population responses and to generate hypotheses that can be tested via additional research and monitoring of restoration efforts. In our case study river network in Oregon, model results under future warming scenarios indicate high probability of extinction for a cold-water salmonid, with substantial expansion by some, but not all, cool-water fish species. Larger, lower-gradient stream reaches may experience substantial shifts in fish species assemblages with strong species interaction effects on assemblage structure. Smaller headwater streams are more strongly influenced by colonization/extinction events associated with physical habitat dynamics. Opportunities for managing and influencing future trajectories through habitat restoration, water quality improvements, or mitigation of disturbances such as wildfire also differ across the watershed. These results and highlight the importance of considering the joint effects of physical, ecological, and social (human) dynamics on future fish populations.