Vulnerability of Coastal Cutthroat Trout to Changes in Stream Temperature and Flow in Coastal Streams of the Pacific Northwest of North America

Throughout the range of Coastal Cutthroat trout in western North America, stream temperature and flow are expected to become more variable leading to increases in uncertainty related to how they will influence trout. Although streamflow is tightly coupled with stream temperature currently, their relationship could change into the future. Here, we use a scenario-neutral approach to evaluate the sensitivity of Coastal Cutthroat Trout (Oncorhynchus clarkii clarkii) populations to a plausible range of gradual changes expressed as separate and combined effects of stream temperature and flow. We use an individual-based model heavily parameterized with field data of geophysical template, trout abundance, and environmental regimes collected in Coastal streams of California and Oregon. The model tracks individual trout through daily processes of spawning, movement, feeding, growth, and mortality for six decades. Our results show that stream-trout persist with extreme changes in temperature and flow, but with seriously reduced biomass. Minimal changes to stream temperature and flow lead populations to maintain or increase biomass, but the window of resistance varies by stream. Our findings provide managers with enough information on trout responses to incorporate new climate change projections that may arise from new climate models when they are available.