Schindler, DanielChambers, Nicholas2025-08-012025-08-012025-08-012025Chambers_washington_0250O_28598.pdfhttps://hdl.handle.net/1773/53650Thesis (Master's)--University of Washington, 2025The spatial scale of dispersal during early life stages when mortality rates are high is essential for understanding the relationship of the distribution of spawners to population productivity. In this study, we quantified the fine-scale distribution of age-0+ (fry) steelhead (Oncorhynchus mykiss) near redds across multiple sites in the Skagit River, WA. The estimated mean downstream displacement of fry was 145m with 95% of fry remained within 312m of their natal redd. Evidence of density-dependent dispersal was found at sites with multiple redds, where mean displacement increased to 270 m, though individual kernel tails could not be resolved. This limited dispersal resulted in strong spatial clustering of fry in areas with multiple redds. To evaluate effects of limited dispersal, we applied simulated dispersal kernels to ten years of spatially located redds to simulate fry distributions across a 31.5 km stream network, scaling each kernel to represent the same number of potential fry. The distance of stream channel accessed by fry increased linearly with increasing redd abundance, demonstrating spatial expansion and contraction of spawners in relation to abundance. Core spawning areas were consistently reused across years, with higher proportions in core areas in low abundance years. Increasing spawner abundance led to a shift in the proportion of fry from a majority in low density areas to a majority in high density areas. This provides strong evidence that density dependence was present across the range of observed spawner densities. Despite the change in average fry density, the number of fry in low density areas remained relatively constant due to spatial expansion of spawners. Expansion into heterogenous habitats would lead to habitat mediated effects on recruitment, where if habitat quality is spatially uniform then expansion would increase recruitment proportionally with spawner abundance. Our findings highlight the importance of incorporating spatial structure and fry-scale dispersal into models of habitat capacity and recruitment, particularly when evaluating restoration or harvest strategies aimed at conserving the full range of life-history diversity.application/pdfen-USCC BYAquatic sciencesFisheriesThesis