Evaluating the robustness of management procedures for the Sablefish (Anoplopoma fimbria) fishery in British Columbia, Canada for 2017-18
The British Columbia (BC) Sablefish (Anoplopoma fimbria) harvest strategy is designed around a management procedure (MP) that is simulation-tested against multiple operating model (OM) scenarios that represent a range of hypotheses about Sablefish stock dynamics and fisheries. The underlying OM used to generate hypotheses about Sablefish stock and fishery dynamics was recently updated to include several structural changes (DFO 2016). A regional peer review meeting was held on January 10, 2017, to evaluate the performance of the current Sablefish MP and alternative MPs using the revised 2016 OM.
The current MP uses a harvest control rule with a maximum harvest rate set at the estimated harvest rate at maximum sustainable yield (UMSY), as well as a minimum total allowable catch (TAC) floor of 1,992 tonnes (t) and a minimum size limit of 55 cm. Nine alternative MPs that differed in their use of TAC floors (0; 1,800; or 1,992 t), phase-in periods to a new maximum harvest rate (0, 3, 4 or 5 years), and sub-legal release regulations (release Sablefish < 55 cm or full retention with all Sablefish catch counted towards the TAC) were also evaluated. Each of the alternative MPs had a maximum harvest rate of 5.5%.
The revised Sablefish OM was fitted (or conditioned) to stock monitoring and fishery data collected between 1965 and 2016. Five operating model scenarios were used to capture uncertainty in both stock productivity and female spawning biomass in 2016 (fSSB2016). The base case OM used the mean or expected combination of productivity and fSSB2016, while the other four OM scenarios represented the following combinations:
high productivity, mean fSSB2016 (hiProd/expSSB);
low productivity, mean fSSB2016 (loProd/expSSB);
mean productivity, high fSSB2016 (expProd/hiSSB); and
mean productivity, low fSSB2016 (expProd/loSSB).
Estimates of female spawning stock biomass in 2017 (fSSB2017) were above the limit reference point (LRP) of 0.4BMSY but below the long-term target of BMSY in four of the five OM scenarios, where BMSY is the female spawning biomass at maximum sustainable yield (MSY). Estimated fSSB2017 in the expProd/loSSB scenario was below the LRP (fSSB2017/BMSY = 0.38). Estimates of fSSB2017/BMSY ranged from 0.42 to 0.46 among the other four OM scenarios.
Performance of the 10 MPs was measured relative to five objectives for the BC Sablefish fishery (three conservation objectives and two fishery catch objectives) that were developed via consultations between fishery managers, scientists, and industry stakeholders. MP performance was ranked within each of the five operating model scenarios, as well as weighted across scenarios.
When evaluated against the revised OM (DFO 2016), the current MP was unable to meet the three conservation objectives under any of the five productivity-spawning biomass OM scenarios and was consistently ranked last in conservation performance. It is recommended that consideration be given to alternative MPs for the Sablefish fishery.
Based on the weighted-average performance across the five OM scenarios, MPs that included TAC floors were not able to achieve conservation objectives while MPs without a TAC floor were able to achieve these objectives. The length of the phase-in period to a lower maximum harvest rate did not have a large effect on MP performance relative to conservation objectives.
MPs that include the addition of full retention (here meaning all sub-legal (< 55 cm) and legal fish caught are counted against the TAC) resulted in better performance against conservation objectives relative to the identical MPs without full retention.
Neither the current nor any of the alternative MPs achieved fSSB levels above BMSY, or 0.8 BMSY in 50% of the years measured over two Sablefish generations (the third conservation objective), although some MPs were able to increase spawning biomass to 0.8 BMSY by the end of two Sablefish generations (36 years). It is recommended that the trade-offs between achieving 0.8 BMSY in 50% of the years over two Sablefish generations (the current objective) and achieving 0.8 BMSY in two Sablefish generations be further examined.
In the absence of full retention of Sablefish, an MP with a phase-in to a new maximum target harvest rate of 5.5% over 5 years was able to achieve two of the conservation objectives while providing 10-year average catch of 1,690 t, which is below the current TAC floor of 1,992 t.
The revised operating model continues to assume that the BC Sablefish stock is a closed population, despite evidence of movements among Sablefish stocks along the west coast of North America. These movements may have implications for the assumptions made about Sablefish stock dynamics in BC (i.e., recruitment, productivity) that are not currently captured by the revised OM or reflected in MP performance evaluations.
Inconsistent sampling of age composition data in commercial catches (only Trap fishery age composition data are currently available) has contributed to model issues that have been consistently identified during the BC Sablefish management strategy evaluation (MSE) process (Cox et al. 2011; DFO 2011, 2014). It is recommended that attention be given to designing and implementing a commercial catch sampling program across all fishery sectors.
MSE is an iterative process of change and improvement. It is recommended that BC Sablefish operating models and MPs be reevaluated for suitability at 3-year intervals.
This Science Advisory Report is from the January 10, 2017 regional peer review of Evaluating the robustness of management procedures for the Sablefish (Anoplopoma fimbria) fishery in British Columbia, Canada, for 2017-18. 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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