UC Santa Cruz

Populations of anadromous Pacific salmon and steelhead are increasingly threatened by degradation and loss of critical freshwater habitat, as well as poor survival at sea. Coho salmon (Oncorhynchus kisutch) populations in California, which represents the southern limit of the species' range, are particularly vulnerable to such environmental disturbances. Accordingly, all California populations are listed under the Endangered Species Act and have been placed into two Evolutionarily Significant Units (ESUs): the Southern Oregon/Northern California Coast (SONCC) ESU, which is listed as threatened; and the Central California Coast (CCC) ESU, which is listed as endangered. Despite these protections, many populations are threatened with extirpation and natural productivity is severely impacted by the lack of natural habitat. In order to facilitate recovery, several integrated recovery and conservation hatchery programs operate within these ESUs. However, how effectively these programs contribute to production in these high-risk populations has yet to be quantified, which prevents the development of evidence-based mitigation strategies that aim to incorporate artificial propagation.

In chapter one, I use pedigree reconstruction tools to understand current reproductive dynamics of coho salmon in the Shasta River, CA. I particularly focus on evaluating the contribution of excess adults released from the nearby Iron Gate Hatchery (IGH) to production within the Shasta to determine the efficacy of directly supplementing the Shasta population with these hatchery releases. Less than 10% of the juveniles sampled in the Shasta each year were assigned to IGH releases, suggesting low reproductive success amongst these individuals within the Shasta River. In chapter two, I assess the efficacy of the current Captive Broodstock program at Kingfisher Flat Hatchery on Scott Creek, CA. I again use pedigree reconstruction methods to perform parentage-based assignment for juveniles collected in Scott Creek, CA against a parental pool of adults that spawned both within the hatchery and the creek. Few Captive Broodstock adults were recovered as parents, again suggesting low reproductive success amongst these individuals.

I ultimately discuss the implication of these results with respect to management, indicating measures that may optimize both ongoing and proposed conservation strategies to ensure long-term stability within these imperiled populations of coho salmon.