Science Advisory Report 2021/006

Science Guidelines to Support Development of Rebuilding Plans for Canadian Fish Stocks

Summary

• Under the revised Fisheries Act a rebuilding plan is required when a stock falls to or below its Limit Reference Point (LRP). The LRP should be avoided with high probability to reduce the risk of serious harm and management actions to prevent further decline in stock status should be implemented before this point is reached.
• Unless otherwise defined in stock-specific precautionary approach frameworks, the LRP should be considered breached if the terminal year stock status indicator is estimated to be at or below the LRP with a greater than 50% probability or if the projected stock status indicator falls below the LRP with a greater than 50% probability under a zero catch scenario in a 1 year projection.
• Stock status and fishing mortality should be expressed in a probabilistic manner with respect to reference points and targets. Where probabilities cannot explicitly be estimated, qualitative likelihood approaches may be required.
• A rebuilding plan requires the establishment of a rebuilding target. There should be a high probability that the stock is above the LRP when the target is achieved. Furthermore, there should be a low probability of the stock falling below the LRP in the short to medium term.
• Measurable rebuilding objectives should be defined, including objectives related to the rebuilt state. Where possible, environmental conditions and biology should be taken into account when setting objectives.
• Rebuilding objectives may include outcomes other than those related to biomass, such as expanding or maintaining spatial distribution, subpopulations and age structure, and creating the conditions that are expected to promote such outcomes. Consideration should be given to prioritizing among objectives to facilitate decision-making, with stock growth being a high priority.
• Based on scientific literature, actions to rebuild a stock should be taken as soon as possible to avoid further deterioration of stock status and increase the likelihood of rebuilding success.
• A minimum rebuilding timeline should be established against which alternative management actions can be evaluated. The standard is to estimate the time to reach the rebuilding target with zero fishing mortality (T_min). In the absence of T_min, alternative metrics of rebuilding time can be used, such as generation time.
• Where possible, future stock states should be projected for a range of plausible scenarios and candidate management measures. Scenarios are hypotheses about stock and fishery dynamics that may be affected by various factors including environmental conditions. Projections should include a zero fishing mortality and status quo scenario to serve as a benchmark for comparison with alternative strategies.
• Attribution of stock depletion to environmental factors should not be taken as an indication that fishing mortality has little or no effect without evidence that is the case. Where rebuilding prospects appear to be poor even in the absence of fishing mortality, this prognosis should be explicitly described.
• Advice on whether habitat loss or degradation has likely contributed to the stock’s decline is required.
Rebuilding strategies need to be evaluated relative to defined objectives and associated performance measures.
• Evaluation should occur during development and implementation of the plan. Advice should be provided on the frequency of evaluation and the monitoring information that is needed to evaluate rebuilding performance.

This Science Advisory Report is from the January 14-16, 2020 National Peer Review meeting on Science guidelines to support development of rebuilding plans for Canadian fish stocks. 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 2021/006 (PDF, 349 KB)

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