Abstract: More than half of global stream networks are non-perennial, and the frequency and duration of stream drying events are projected to increase globally due to climate change and human activities. By studying trophic interactions in non-perennial streams, we can better understand how these systems function and inform management strategies for their conservation in both natural and human-altered contexts. Recent research highlights the use of non-perennial streams by terrestrial and aquatic organisms, including spawning habitat by endangered steelhead (Oncorhynchus mykiss) and coho salmon (Oncorhynchus kisutch) of the Pacific Northwest. Whether these fish are simply surviving in these systems or benefiting from unknown advantages remains unclear. Our goal is to determine if differences in prey availability in perennial and non-perennial habitats are a factor influencing steelhead use of non-perennial streams. We collected diet samples of wild juvenile steelhead (n=100 individuals) and benthic invertebrate communities (n=24 samples) from both perennial and non-perennial sections of Thirtymile Creek, a high desert stream in Oregon, USA, from May through July 2022. We compared the biomass, abundance, and diversity of the steelheads’ diets and the benthic invertebrate communities between the two habitats. Steelhead diets in non-perennial sections had a 6.3% higher biomass and 38.7% more individuals compared to perennial sections. This suggests that while non-perennial habitats may offer higher abundance of prey, prey may be smaller, requiring more effort to reach higher gut biomasses. Further analyses using nonmetric multidimensional scaling (NMDS) of invertebrates collected from non-perennial and perennial sections will allow us to explore how different environmental variables in the two habitats influence steelhead diet and macroinvertebrate communities. Overall, our findings can inform conservation practices for steelhead in different stream habitats by exploring the dynamics of habitat-specific dietary patterns. Understanding how organisms subsist in non-perennial systems can help protect endangered species such as salmonids and preserve unique biodiversity in changing environments.
