Growth of coastal cutthroat trout, Oncorhynchus clarkii clarkii, in intensively monitored urban and natural streams in Puget Sound and the Strait of Juan de Fuca

Coastal cutthroat trout ( Oncorhynchus clarkii clarkii ) are considered indicators of stream health, yet paradoxically, they often persist in degraded urban watersheds. To evaluate how cutthroat trout perform in a small urban watershed, we compared several indices of fish size and growth in a small, highly urbanized stream in Seattle, Washington (Pipers Creek) with populations from three larger, forested, watersheds in nearby Strait of Juan de Fuca. We used single sample measures like size and relative condition factor (Kn). We also employed mark-recapture data from PIT-tagged fish to compare multiple performance metrics, including von Bertalanffy growth models, and bioenergetic estimates of food consumption (P Cmax ). The salmon community composition differed dramatically between systems: Pipers Creek was dominated by cutthroat trout (96%), whereas they were a minor component (1%) in the forested streams, which were dominated by coho salmon and steelhead in summer months. Cutthroat trout from the urban stream were also smaller on average and exhibited a lower maximum body size, suggesting a life history favoring earlier anadromy, yet they were in slightly better body condition. Despite these differences and the degraded nature of Pipers Creek, we found no difference in year-over-year growth rates between the two systems. Bioenergetic analysis supported this finding, indicating that growth in both environments was similarly constrained by food availability, with fish in both systems consuming less than 50% of their maximum potential ration. The similarity in growth among urban and more natural stream highlights the remarkable life history plasticity of cutthroat trout. This resilience allows them to exploit marginal habitats effectively, suggesting that their performance may reflect the species’ adaptability as much as it does the quality of the habitat itself.