Coherence of observed adult sockeye salmon abundance within and among spawning habitats in the Kvichak River watershed

Stewart, Ian; Hilborn, Ray; Quinn, Thomas

Despite coherent trends in aggregate abundance of Pacific salmon Oncorhynchus species at ocean-ba-sin scales, individual populations often fluctuate out of phase with one another. However, spatial covariation in shared environmental conditions may lead to correlation among proximate populations in survival, recruitment, and sub-sequent adult abundance. We found strong covariation in 45 years of aerial abundance estimates of adult sockeye salmon Oncorhynchus nerka in 93 spawning populations in the Kvichak River system, Bristol Bay, Alaska. A significant negative relationship with geographic distance (P<0.01) accounted for just 2.96% of the variability in both correlation of abundance between populations, and a related similarity coefficient. There was no evidence for athreshold of rapid decay in this relationship, despite distances of up to 175 km between populations. Island beaches showed significantly higher covariation (P<0.05) than other types of spawning habitat, even after removing the effectof distance. We conclude that these patterns are likely a result of the commercial fishery, broad environmental patterns experienced by populations throughout the drainage, and differences in population-specific early life historysurvival rates among habitats. A better understanding of the degree to which spawning sites show covariation in abundance, as well as of patterns present within a single river system, could assist researchers in locating suitablecontrol sites for experiments and may allow for more accurate interpolation of missing historical data.

Coherence of observed adult sockeye salmon abundance within and among spawning habitats in the Kvichak River watershed

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