Science Advisory Report 2019/056

Technical Review of stream-type Fraser River Chinook Management Approach

Summary

• Conservation concerns for three stream-type Fraser River Chinook Salmon Stock Management Units (SMUs; Spring 4₂, Spring 5₂ and Summer 5₂) led to implementation of a series of fisheries closures and restrictions that were initiated in 2008, then expanded in 2010 and again in 2012. The 2012 management measures were outlined in a letter written by the Regional Director General for DFO’s Pacific Region to First Nations and stakeholder groups (referred to as the ‘2012 RD Directive’).
• As part of the 2012 management measure implementation, a two-phase process was established to review DFO’s management approach for stream-type Fraser River Chinook Salmon to determine whether the approach had achieved its intended conservation and allocation objectives consistent with An Allocation Policy for Pacific Salmon (1999). Phase 1 provides a technical review of the data and methods available to assess the fisheries impacts resulting from the management measures on stream-type Fraser River Chinook Salmon and is the subject of this review.
• Data were compiled from technical reports and Fraser-area stock assessment programs to examine trends in escapement, biological properties and annual exploitation rates. Fishery- and sector-specific exploitation rate indices for each SMU were estimated via two approaches for allocating fishery catch to SMU: the first approach used coded wire tag (CWT) data, and the second used an updated Run Reconstruction model supplemented with genetic stock identification (GSI) information for marine fisheries. The latter approach was used as a basis for evaluating management performance relative to management objectives taken from the 2012 RD Directive.
• A sensitivity analysis of the Run Reconstruction approach was conducted to investigate the potential effects of uncertainty in assumptions or systematic biases in data inputs on resulting estimates of management performance. An uncertainty analysis was used to demonstrate the extent to which the magnitude of uncertainty in data inputs and parameters affected the level of uncertainty in resulting model outputs.
• Results show that all three stream-type SMUs exhibited depressed escapement in recent years, and consistent declines over the last four years. There is also preliminary evidence of recent declines in size-at-age for some populations within SMUs which may, if the changes continue, affect selectivity of fisheries and the potential effectiveness of size-based management measures.
• Estimated fishery- and sector-specific exploitation rate indices based on the Run Reconstruction approach show that, while it is possible that overall reduction targets for exploitation rates on Spring and Summer 5₂ Chinook were met, considerable uncertainty in the input data and model assumptions precludes a definitive conclusion at this time. In particular, existing assumptions around fishing-related incidental mortality (FRIM) rates (that were used in this analysis) may underestimate the true impacts of FRIM, which could lead to an underestimation of total mortality.
• Results show that reductions to First Nations fisheries were likely higher than intended, while recreational and commercial reductions were likely lower than intended. However, results showed that when random error was introduced to input data and model parameters, measurement of the distribution of ‘harvest impacts’ (which includes both landed catch and fishing related incidental mortality) among sectors was highly uncertain, even for the low uncertainty scenario. This result was especially true for recreational and commercial sectors that relied on GSI sampling of marine catch composition.
• While the objectives of this process were deemed to have been met (as stated in the Terms of Reference), several items were identified as future work to improve subsequent iterations of these analyses. In particular, the need for a more rigorous assessment of fishery- and sector-specific FRIM impacts (identified during a previous Canadian Science Advisory Secretariat (CSAS) process) was highlighted, as was the need for an integrated modelling framework for estimating fishery-specific exploitation rates from both in-river and marine fisheries. Other areas for future investigation include: incorporating a cumulative effects approach to the sensitivity analyses (rather than assessing each factor singly); improved run timing information; further work to improve GSI baselines and stock identification to the SMU level; consistent annual sampling of fishery catch (for both CWT recoveries and GSI samples); and, a more comprehensive estimation of uncertainty around exploitation rate estimates, including stock assignment error when using GSI methods.
• It was recognized that this type of analysis would benefit from improved documentation and transparent availability of data and assessment methods, as well as routine publication of this information in citable sources and retrievable databases.

This Science Advisory Report is from the July 9-10, 2019 regional peer review on the Technical Review of Fraser River Chinook Management Approach. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

Science Advisory Report 2019/056 (PDF, 702 KB)

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