Science Advisory Report 2010/070

Guidelines for applying updated methods for assessing harvest rules for Fraser River sockeye salmon (Oncorhynchus nerka)

Summary

• The Fraser River Sockeye Spawning Initiative (FRSSI) has been an eight-year process to develop guidelines for setting annual escapement and exploitation targets for Fraser Sockeye Salmon stocks. The initiative began in early 2002, and has since evolved through a series of workshops and on-going feedback from stakeholders.
• A quantitative modeling tool (FRSSI Model), used to support the planning process for Fraser River Sockeye Salmon, was developed and reviewed in 2003. The model has evolved substantially since. This asseslang="la"sment evaluates the assumptions and performance of the revised model.
• The FRSSI Model is intended as a formalized, quantitative tool for exploring the expected long-term performance of escapement strategies for Fraser Sockeye Salmon under a wide range of alternative assumptions (e.g. population dynamics, future changes in productivity).
• The FRSSI Model currently simulates 19 stocks of Fraser Sockeye Salmon forward for 48 years and applies different long-term escapement strategies chosen by the user. It tracks the performance of management groups as well as individual stocks, and is set up to explore many variations of management approaches that are applied on an annual basis: (1) fixed escapement, (2) fixed exploitation rate, and (3) varying total allowable mortality with run size. For each of these, the effect of overlap in return timing can be evaluated.
• The model allows users to confront a chosen strategy with a wide range of scenarios: (1) alternative spawner-recruit models, (2) alternative future patterns of productivity, (3) alternative assumptions about en-route mortality, and (4) alternative assumptions about pre-spawn mortality. All stocks within a management group are exposed to the same exploitation rate and environmental mortality.
• Use of the revised model [FRSSI (2010) Model] in support of Fraser River Sockeye Salmon planning is recommended.It was agreed that the alternative assumptions currently available in the FRSSI model establish reasonable bookends on plausible scenarios, and allow end-users to explore a comprehensive suite of “what-if” scenarios in a collaborative planning process.
• Recommendations for future analyses and model modifications include: (1) updated estimates of productive capacity for Fraser Sockeye Salmon lakes, (2) alternative future scenarios for en-route mortality, (3) development of a plausible suite of stock-specific future patterns in productivity due to differences in habitat and environmental conditions among stocks, (4) estimation of depensation thresholds and quasi-extinction thresholds for each of the Fraser Sockeye Salmon stocks, and (5) further analyses of alternative spawner-recruit models and their implications.

This Science Advisory Report has resulted from the Fisheries and Oceans Canada, Canadian Science Advisory Secretariat Pacific Regional Advisory Meeting of May 26-27, 2010 on Cultus Lake Sockeye Stock Status, 2010 Barkley Sound Sockeye Forecast, 2010 West Coast Vancouver Island Chinook Abundance Forecast, and the Fraser River Sockeye Spawning Initiative. Additional publications from this process will be posted as they become available on the DFO Science Advisory Schedule.

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