Science Advisory Report 2022/030

Methodologies and Guidelines for Defining Limit Reference Points for Pacific Salmon

Summary

• The amended Fisheries Act (2019) includes new Fish Stocks provisions that introduce legal obligations to identify limit reference points (LRPs) for major fish stocks prescribed under regulation. For Pacific Salmon, Stock Management Units (SMUs, DFO 2022) consisting of one or more Wild Salmon Policy Conservation Units (CUs) are proposed as ‘major fish stocks’.
• These provisions create the demand for methods to estimate LRPs and status at the SMU level, while considering the Wild Salmon Policy (DFO 2005) goal to maintain component CUs above their lower benchmarks in part to conserve adaptive diversity.
• LRPs are also required under DFO’s Precautionary Approach (DFO 2009) and other domestic and international commitments.
• Candidate LRP methods were applied to three case study SMUs. Lessons learned from case studies were used to inform the development of guidance for implementing LRPs, which is presented in the form of a stepwise process.
• SMU-level LRPs that are based on the status of component CUs are recommended to meet requirements of the Fisheries Act, called ‘CU status-based LRPs’. Under this approach, it is recommended that an SMU be considered below the LRP if at least one CU within the SMU is in the Red zone, as assessed under the WSP (i.e. below its lower benchmarks). Lower benchmarks are identified at levels to allow a substantial buffer against extinction risk and are proposed to represent levels above serious harm.
• CU status is derived from a composite of metrics, as recommended for assessments under the Wild Salmon Policy (Holt et al. 2009).
• Under the amended Fisheries Act, a rebuilding plan will be required for prescribed SMUs that are below their LRP, though the assessment of an SMU below its LRP does not necessarily trigger specific fishery management measures. Actions to support rebuilding may occur at a variety of spatial scales using a range of management measures relevant to Pacific salmon, which may include habitat restoration and hatchery enhancement at watershed and sub-watershed scales.

• When estimating ‘CU status-based LRPs’, the status of data-deficient CUs can potentially be inferred from data-rich CUs within an SMU when there is sufficient evidence that the CUs have similar threats, environmental conditions, life-history characteristics, and carrying capacities. In the absence of such evidence, the default assumption is that the status of data-deficient CUs cannot be inferred from other CUs in the SMU.
• When status is inferred for data-deficient CUs within an SMU and status of all data-rich CUs have statuses above the Red zone, it is recommended that SMU status be above the LRP but considered more uncertain than if there were no data-deficient CUs. When at least one data-rich CU is Red, then SMU status is below the LRP regardless of the presence of data-deficient CUs.
• Uncertainty in ‘CU status-based LRPs’ can arise from uncertainties in CU benchmarks, the choice of metrics, and associated CU statuses.
• ‘Aggregate abundance LRPs’ based on SMU-level abundances were identified to approximate 'CU status-based LRPs’. However, case study analyses showed that these methods had numerous assumptions and uncertainties and did not necessarily represent CU status. As a result, aggregate abundance LRPs are not recommended to address Fisheries Act requirements. However, they may be considered for specific fisheries management contexts where aggregate abundance reference points are required, and are included as supplemental approaches in the stepwise guidance procedure described here.
• The LRP methods presented here do not explicitly account for serious harm to ecosystems and associated species, or the role of ecosystems and habitats on the sustainability of wild Pacific salmon. Future research is needed to fill these gaps and better align the proposed methods with DFO’s Precautionary Approach Framework (DFO 2009) and the Wild Salmon Policy (DFO 2005).
• Engagement and collaboration with Indigenous Peoples is recommended to pair Indigenous Knowledge with the guidance presented here when establishing LRPs.
• Additional next steps on defining LRPs include research on time-varying parameters and impacts on LRPs, and the development of guidance on metrics and benchmarks of distribution of spawning among populations within CUs.

This Science Advisory Report is from the March 2-4, 2022 regional peer review on the Methodologies and guidelines for developing Limit Reference Points for Pacific Salmon in British Columbia. 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 2022/030 (PDF, 763 KB)

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