Science Advisory Report  2014/038

West Coast Vancouver Island Chinook Salmon Escapement Estimation and Stock Aggregation Procedures

Summary

• Canada is required to assess the escapement of West Coast Vancouver Island (WCVI) PST extensive indicator stocks relative to escapement goals annually and estimate the abundance for the entire WCVI Chinook salmon management unit as part of the implementation of the Chinook Salmon Annex of the Pacific Salmon Treaty (PST). Similar assessments of individual stocks and aggregate stock groupings are required to implement Canada’s Wild Salmon Policy and meet other domestic management needs
• Periodic visual surveys are used to estimate escapement of WCVI Chinook salmon extensive indictor stocks. A Canadian Science Advisory Secretariat (CSAS) Regional Peer Review was held to i) evaluate the escapement estimation methodology used to evaluate the abundance of WCVI extensive indicator stocks relative to escapement targets, and ii) recommend methods for estimating an annual aggregate escapement or appropriate surrogate for the entire management unit.
• The periodic visual survey methodology was evaluated to assess the validity of the method considering biological, distributional and logistical factors specific to WCVI Chinook salmon, the ability of the methods to produce a measure of uncertainty and the potential for bias in the survey procedure.
• This review concluded that the current application of the method to estimate stream escapement does not provide estimates of uncertainty. Several sources of uncertainty and bias were identified, including the estimation of observer efficiency, survey life, the frequency of site visits and the identification of peak counts.
• Approaches for investigating the sensitivity of the estimates of escapement to these biases, as well as approaches for the evaluation of the bias and the development of correction factors were identified. Refinements of the Area-Under-the-Curve (AUC) and Maximum Likelihood (ML) estimation models, data inputs, and further development of both estimation models, as well as thorough documentation of protocols and analytical methods, are recommended.
• Given the further analysis and revisions required to provide advice on the validity of the current visual survey method, it was recommended that these initiatives be completed and the technical document resubmitted for peer review.
• Four methods of estimating aggregate salmon escapement were presented by contributors that have been used to assess Chinook and coho salmon in other spawning areas in B.C., as well as Alaska and Oregon. When these methods were evaluated by the scale and specific management objectives of WCVI Chinook salmon, elements of the Generalized Random Tessellation Stratified (GRTS) and the habitat based methods were identified that could improve the current WCVI methodology. It was also recommended that the fishery-based method be applied, giving an estimate of aggregate abundance independent of the visual escapement estimates, and results compared to the estimate based on visual surveys.

This Science Advisory Report is from the June 18-20, 2013, West Coast Vancouver Island Chinook Salmon Escapement Estimation and Stock Aggregation Procedures Regional Peer Review. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

Complete document (PDF, 124 KB)

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