Détermination de la taille de la remonte propre au stock de saumon rouge du fleuve Fraser

Résumé

Postseason run size estimates for Fraser Sockeye stocks are used to forecast future returns, report exploitation rates and en route mortality estimates, and conduct stock assessments. Run sizes for most Pacific salmon stocks are the sum of catch and spawning escapement estimates; Fraser Sockeye is unique in that it also includes estimates of stock-specific en route mortality that have accounted for adverse environmental and biological conditions. Stock-specific estimates of en route mortality for Fraser Sockeye have been increasing and can often exceed catch and occasionally spawning escapement in overall contribution to run size calculations. The current Fraser Sockeye postseason run size determination process, ongoing since 2009, is designed to improve postseason run size estimates by incorporating stock-specific en route mortality and scrutinizing the main components of the run size process—catch, spawning escapement, and en route mortality. An in-depth documentation and review of the process used to estimate postseason stock specific run sizes was provided with a focus on catch, escapement, and en route mortality, as well as uncertainty and input sensitivity in component error. Recommendations for improvements to the current stock-specific run size estimation process and guidance on use of the data sets generated by this process were provided. Major recommendations include the following: simplify the overall postseason run size structure; update the visual survey estimates to improve accuracy of spawning escapements; receive consistent and timely reporting of catch from all fisheries that have a reasonable potential to intercept Fraser Sockeye; update and extend en route mortality models to include all evaluated stocks; and work to quantify uncertainty in all inputs and outputs. A summary table of recommendations was developed along with evaluation criteria to assist with prioritization based on different end user objectives. Quantifying and reducing the uncertainty in run size components will support credibility for downstream uses, including exploitation rate and productivity analyses, and for estimating the impact of en route mortality. The postseason run size and its component data sets should be used for postseason evaluations of run size, exploitation rates, and productivity, as well as forecasting and assessments supporting long-term planning. At present, they should not be used for evaluations of in-season management or evaluations requiring underlying daily estimates. Large bias and imprecision of some stock-specific run size components and their derivatives require additional scrutiny for use (e.g., exploitation rates for small stocks). Better understanding and quantification of en route mortality will also support the Department’s recovery and rebuilding plans for Fraser Sockeye and other salmon populations, especially given the expected increased frequency of extreme migration conditions and reductions in catch and/or spawning escapements.