Selbie, D. | Search bioRxiv

bioRxiv2026

Climate Impacts on Sockeye Salmon Productivity Vary Across Life Stages and Regions

Many Sockeye salmon (Oncorhynchus nerka) populations have declined over recent decades, and climate change is likely to exacerbate these declines through direct and indirect ecological effects. The response to the associated environmental changes is likely to vary among life stages, populations, and regions. Quantitative estimates of climate change driven impacts that account for this variability could fill a critical gap and provide forward-looking insights into how sockeye are expected to respond to future climate-driven change across their lifecycle. To address this need we developed a hierarchical population dynamics model parameterized with juvenile, adult return and spawner abundance data from 13 sockeye salmon populations from Washington State to northern British Columbia. We used a formal causal inference framework that paired salmon abundance data with a suite of environmental covariates hypothesized to represent ecological conditions across the lifecycle. We used the model to estimate population-specific responses to each environmental driver, then combined parameter estimates with projections from down-scaled climate change models to estimate productivity responses to anticipated environmental change. We found that historical sockeye productivity was strongly associated with environmental covariates, which explained more interannual variability in return abundance than spawner abundance in most populations. However, the life stages and specific environmental covariates with the largest impacts differed among populations and regions, often displaying a latitudinal gradient. Increases in coastal ocean temperatures and mixed layer depth generally had negative effects though they varied among regions. Increased freshwater summer rearing and return migration temperatures had weaker but consistently negative effects. Under future climate conditions, projected changes in these environmental covariates are expected to result in substantial declines in productivity across most populations. Sockeye salmon display varying degrees of sensitivity to climate change across life stages, populations, and regions. Effective future management will require explicitly accounting for these life stage and population-specific responses.

ecology↗

bioRxiv2026

Changing Pacific salmon nursery lake ecosystem dynamics over centuries to millennia: insights from sedimentary DNA metabarcoding

Pacific salmon are keystone species to North Pacific freshwater, coastal, and oceanic ecosystems, but many populations have declined or become more variable in recent decades due to anthropogenic impacts and climate change. Long-term records are needed to understand past changes, identify ecosystem stressors, and guide restoration. We used sedimentary DNA (sedDNA), an emerging paleoecological approach offering broader taxonomic information than traditional methods, to reconstruct ecosystem changes across five Pacific salmon nursery lakes in British Columbia (Canada). DNA metabarcoding targeting the 18S ribosomal RNA gene V7 region was used to track shifts in eukaryotic communities including algae and invertebrates over centuries to millennia. Most lakes showed notable algal community shifts over the past two centuries, with declining green algae and rising diatom relative abundances. Chrysophytes and dinoflagellates also increased over the past century in most lakes, likely driven by stronger thermal stratification, which favored these motile and mixotrophic algae that are capable of vertical migration and flexible nutrient acquisition. We contextualized the trajectories of each core through an ordination analysis based on 98 lakes distributed across British Columbia, which identified land-use changes and longer growing seasons as potential drivers. Network analyses of the sedDNA time series revealed decreasing modularity and increasing connection across lakes, suggesting a shift in resilience mechanisms from between-module buffering by compartmentalized specialists to within-guild insurance via functional overlap among generalists. Our findings demonstrate that sedDNA provides taxonomically rich, long-term insights into aquatic ecological dynamics, which are foundational for understanding and protecting Pacific salmon nursery habitats.

ecology↗