Research Document 2019/032

Evaluating the robustness of management procedures for the Sablefish (Anoplopoma fimbria) fishery in British Columbia, Canada for 2017-18

By Sean Cox, Kendra Holt, and Sam Johnson

Abstract

Fisheries and Oceans Canada (DFO) and the British Columbia (B.C.) Sablefish (Anoplopoma fimbria) fishing industry have collaborated on a management strategy evaluation (MSE) process since 2009. This process is used to develop and implement a transparent and sustainable harvest strategy for the multi-gear Sablefish fishery. The underlying operating model used to generate hypotheses about Sablefish stock and fishery dynamics as part of the MSE was recently updated to include several structural changes that improved model fit to data and resulting estimates of historical recruitment. This paper updates the Sablefish MSE by incorporating these improvements to the operating model, and then tests the existing and alternative management procedures for robustness to uncertain stock dynamics. The current management procedure (MP) uses a harvest control rule with a maximum harvest rate (HR) set at the estimated harvest rate at maximum sustainable yield (UMSY), as well as a minimum TAC floor of 1,992 tonnes and a minimum size limit of 55 cm. Nine alternative MPs were also evaluated that differed in their use of TAC floors, maximum harvest rates within the harvest control rule, phase-in periods to a new MP, and sub-legal release regulations. We based our five operating model scenarios on plausible hypotheses about productivity (i.e., the steepness parameter of the spawner-recruit relationship) and current spawning stock biomass. MP performance was ranked within scenarios, as well as weighted across operating model scenarios. Our results show that the current MP was unable to meet conservation objectives under any of the five operating model scenarios. Based on the weighted-average performance across the five 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. 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.

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