Chinook salmon stocks originating from the West Coast of Vancouver Island (WCVI) contribute significantly to the ocean harvests in fisheries in Southeast Alaska and northern British Columbia, as well as being of prime importance to near-shore fisheries along the WCVI itself. Consequently, commercial and sport fishermen, as well as First Nations up and down the coast have a vested interest in the status of WCVI Chinook salmon. Management agencies and organizations responsible for fisheries in Southeast Alaska, northern British Columbia, and along the WCVI have need of stock status information concerning WCVI Chinook salmon.
The overall goal of this project is to estimate the aggregate terminal returns of WCVI hatchery and natural origin Chinook salmon, including catch plus escapement inside the surf line such that the estimates are asymptotically accurate and have a CV of 15% or less. This will be achieved through 1) the first comprehensive assessment of catch plus escapement along the WCVI, and 2) refinement of the ‘driver stock’ approach for estimating aggregate terminal return from a distant fishery.
The “driver stock” approach was first developed through the Sentinel Stock Program, and is based on the assumption that an indicator stock (or stock group) experiences the same exploitation and maturation rates as the aggregate. If the assumption holds, the incidence of this indicator stock group in an ocean fishery (using information such as CWT, otolith, DNA) and in its terminal area would have the same ratio as the catch of the indicator stock group in the same ocean fishery to its terminal run size. When using a single CWT stock, estimating terminal run size is simple. However, given the complexity of the WCVI stock aggregate and terminal WCVI fisheries, the key assumptions of the method – i.e. that maturation rates and exploitation rates are constant across the WCVI aggregate, were not met.
The purpose of this project is to 1) improve the precision of the terminal return estimates of natural and hatchery origin chinook salmon along the WCVI, 2) quantify the variation in maturation, exploitation rates, abundance across the WCVI aggregate, and 3) use the additional information to refine the application of the driver stock approach to the WCVI aggregate through development of a Bayes method. These results will benefit existing stock reconstructions and forecasts in the assessment of the WCVI Chinook salmon stock complex.