Research Document - 2009/043
Development of precautionary management strategies for the British Columbia sablefish (Anoplopoma fimbria) fishery
By S.P Cox, A.R. Kronlund, and M.R. Wyeth
A fishery decision- making framework was recently advanced by Fisheries and Oceans Canada (DFO) that requires application of stock reference points, harvest rules and compliance with the Precautionary Approach. The framework is intended to assure resource sustainability and meet the requirements of various eco-certification programs. This paper describes management procedures for the sablefish (Anoplopoma fimbria) fishery in British Columbia that address each requirement of the DFO precautionary framework. We develop and compare the performance of relatively simple data-based fishery management procedures, which set annual catch limits by combining the preceding year’s catch limits with the recent average of fishery-independent surveys, with model-based procedures that set annual catch limits using constant exploitation rate policies and estimates of stock biomass from productio n or catch-age models. The data-based and model-based procedures we examined employed either constant harvest rate (CHR) or variable harvest rate (VHR) decision rules for setting annual catch limits where the latter addresses a specific DFO precautionary requirement to adjust fishery exploitation rates in response to changes in stock status. All candidate management procedures were tested in stochastic simulations against four operating model scenarios that reflect uncertainties about productivity and current status of the B.C. sablefish stock. In general, VHR decision rules provided consistently better conservation outcomes compared to CHR rules, especially for low productivity scenarios. Data-based procedures provided similar trade-offs between catch and conservation as more elaborate model-based procedures and both types of procedures met inter-annual catch variability objectives. In terms of average annual catch, data-based rules outperformed management procedures based on aggregate production models, while procedures based on catch-age models performed better than data-based rules. Catch-age model procedures were able to track large increases in stock biomass and thus obtain larger average catches under these conditions. Production models consistently under-estimated biomass during periods of population growth and therefore under-exploited growing stocks. Future phases of this work will expand on candidate management procedures and the scenarios against which these procedures are evaluated.
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