| Summary: | Pacific salmon hatcheries support important commercial fisheries for Pink Salmon (Oncorhynchus gorbuscha) and Chum Salmon (O. keta) in Prince William Sound (PWS), Alaska. State policy mandates that hatchery-produced fish not negatively impact natural populations, which can occur in mixed fisheries and via ecological and genetic interactions. Therefore, we quantified the spatial and temporal overlap of natural- and hatchery-origin 1) as they migrated into PWS and 2) in PWS spawning streams. Intensive sampling during 2013-2015, combined with ancillary agency harvest and hatchery composition data, also allowed us to estimate the hatchery, natural, and total run sizes. Estimated annual proportions of hatchery fish in the pre-harvest run ranged from 0.55 (SE = 0.01) to 0.86 (SE = 0.03) for Pink Salmon and from 0.51 (SE = 0.03) to 0.73 (SE = 0.02) for Chum Salmon. Proportions of hatchery fish across all sampled PWS spawning streams were much lower: ranging from 0.05 (SE = 0.03) to 0.15 (SE = 0.07) for Pink Salmon and from 0.03 (SE = 0.03) to 0.09 (SE = 0.03) for Chum Salmon. In both species, relatively high in-stream proportions of hatchery fish tended to be geographically localized, while many streams exhibited low proportions. The estimated total PWS runs were 50-142 million Pink Salmon and 2.3-5.4 million Chum Salmon. Commercial fisheries harvested 94-99% of hatchery-origin fish of both species and 27-50% of natural-origin Pink Salmon and 17-20% of natural-origin Chum Salmon. Despite very high harvest rates on hatchery-produced fish, an estimated 0.8-4.5 million hatchery Pink Salmon and 30-90 thousand hatchery Chum Salmon strayed into PWS spawning streams. Our findings provide context for research on the relative productivity of hatchery- and natural-origin salmon spawning in streams, density-dependent survival, improvements in fidelity to hatchery release sites, influence of hatchery production on escapement management and policy, and refinements in harvest management precision in PWS.
|
|---|