Science Advisory Report 2019/001
Evaluation of Management Procedures for Pacific Herring (Clupea pallasii) in the Strait of Georgia and the West Coast of Vancouver Island Management Areas of British Columbia
Summary
- Pacific Herring (Clupea pallasii) in British Columbia (BC) are managed based on five major stock management areas. This peer review focused on simulation testing of management procedures for two management areas, West Coast of Vancouver Island (WCVI) and Strait of Georgia (SOG) in a process known as Management Strategy Evaluation (MSE).
- Between 2015 and 2018, as part of the MSE process, DFO engaged in a series of objective-setting workshops with First Nations and the herring fishing industry to formulate biological and yield objectives for the fisheries.
- One conservation objective, three biomass objectives, and two yield objectives were developed through consultation between fishery managers, scientists, First Nations and industry stakeholders.
- Biological limit reference points for herring reflect low productivity and low biomass states associated with evidence of serious harm (Kronlund et al. 2018). The Conservation Objective defines a minimum spawning biomass (the LRP) that must be avoided with high probability for consistency with the DFO Decision-making framework (DFO 2009). Subsequent biomass and yield objectives may be ranked in priority but a ranking was not proposed here.
- Three operating models were developed to represent alternative hypotheses describing stock-specific rates of natural mortality (M) over time. The first model (constant-M) includes the assumption that natural mortality is constant over the historical and the projection time frame. The other two time-variant models (density-independent-M, depensatory-M) include the assumption that natural mortality rates vary over time, while differing in the mechanisms assumed to be driving future natural mortality rates.
- Pacific Herring dynamics for stocks in the WCVI and SOG management areas were simulated using single-sex, age-structured operating models (DFO 2015).
- Ten candidate management procedures (MP) were evaluated for both SOG and WCVI. The performance of each management procedure is ranked against the conservation objective.
- Stock status relative to biological reference points was not included in this MSE but will be provided as part of upcoming work on the status of Pacific Herring in 2018 and 2019 forecast.
- For Pacific Herring, key uncertainties include: historical and future trends in natural mortality, steepness of the stock-recruitment (SR) relationship and SR functional form, potential changes in survey coverage and sampling, an unknown relationship between herring biomass and spawn survey index (estimated by the parameter q), and uncertainty in spatial population dynamics.
- The three operating model scenarios presented in the working paper only differed structurally in assumptions about natural mortality, and use operating models based on an assumption that there is a direct linear relationship between the spawn survey index and spawning biomass, i.e., q=1 (Assessment Model 2, DFO 2016). This assumption (q=1) reflects the parameterization of the stock assessment model implemented by Fisheries Management for quota decisions since 2015.
- The working paper demonstrated that the Pacific Herring operating model (DFO 2015) is suitable for simulating realistic data derived from alternative hypotheses about stock and fishery dynamics for WCVI and SOG stocks.
- The sensitivity of WCVI results to future trends in natural mortality suggests additional MP modifications may be required such as criteria that the spawning stock is increasing above the cut-off prior to resuming harvest, i.e., a slow-up MP.
- For Pacific Herring, MPs that implement reductions in harvest rates and application of catch caps can reduce the risk of overharvesting. This finding is applicable to all BC Pacific Herring stocks. However, differences in future trends in abundance presented for WCVI and SOG show the importance of undertaking stock-specific selection of objectives and evaluation of MPs via simulation. Future MSE cycles are likely to result in area-specific MP design. This contrasts with the historical practice of applying the same MP design to all areas.
This Science Advisory Report is from the July 25-26, 2018 regional peer review on Evaluation of Management Procedures for Pacific Herring (Clupea pallasii) in the Strait of Georgia and the West Coast of Vancouver Island Management Areas of British Columbia. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.
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