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bioRxiv · 10.64898/2026.09.25.754467

Temperature and flow impacts on spawner-to-fry production in Okanagan sockeye salmon

Thompson, P. L.·Alex, K.·Stiff, H. W.·Ogden, A. D.
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Abstract

Okanagan sockeye salmon have shown a strong recovery over the past three decades, but the contribution of environmental conditions and management actions to this recovery has not been determined. We developed a hierarchical Bayesian model linking spawner abundances to fry emergence observations to evaluate how flow and water temperature during adult upstream migration and incubation periods influence spawner-to-fry production. Production declined by 62% in years with earlier onset and longer duration of periods when warm river temperatures created barriers to adult migration, indicating that migration conditions can have carry-over effects on reproductive success even when spawners successfully reach the spawning grounds. Additionally, production was 46% lower when flows fell above or below the management target range designed to minimize scour and desiccation during egg incubation. In contrast, we found little support for effects of pre-spawning flows or incubation temperature on production. These findings provide quantitative evidence that current flow management is increasing freshwater spawner-to-fry production and has likely contributed to the Okanagan sockeye recovery. Effective flow management may therefore help offset climate-driven impacts that increasingly threaten this population.

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Thompson, P. L., Alex, K., Stiff, H. W., Ogden, A. D.. 2026-09-28. Temperature and flow impacts on spawner-to-fry production in Okanagan sockeye salmon. https://doi.org/10.64898/2026.09.25.754467

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