Use of otoliths to identify river and hatchery of origin of California Central Valley Chinook salmon in the ocean fishery: potential application to Klamath River Chinook salmon

Ocean harvest models aim to quantify impacts of fishing mortality in the marine environment, with specific mandates to manage the overall resource to minimize impacts on endangered or threatened populations. This creates a particular challenge for managing salmonid resources, given that few tools exist to determine the extent of movement or mixing of stocks in a common marine environment, especially when populations differ significantly in size (McKinnell et al. 1997, PFMC 2001). Current use of coded wire tags provides limited insight into the role of individual natal sources to Chinook salmon population dynamics due to small numbers of tagged fish and even fewer recoveries (<10 % of hatchery releases and far fewer wild fish are tagged). We developed novel techniques to determine whether otoliths (fish earbones) can be used as natural population markers to identify individual sources of salmon from the fall-run California Central Valley (CCV) in adults caught in the ocean fishery. Our research shows that otolith microstructure and geochemical composition provide discrete tags for determining production source (hatchery vs. wild) and individual hatchery and stream-of-origin for adult Chinook salmon. Hatchery and wild individuals can be distinguished with 90 % correc