Research Document - 2012/109

Updated stock assessment for Bocaccio (Sebastes paucispinis) in British Columbia waters for 2012

By R.D. Stanley, M. McAllister, and P. Starr

Abstract

This document provides a stock assessment for Bocaccio in British Columbia waters using data current to 2011.  Results of the work are intended to serve as advice over the short term to managers and stakeholders on current stock status, and likely impacts of different harvest options.  As in previous work, a Bayesian surplus production model was used.  It was fit to one fishery dependent and eight fishery independent biomass indices, and a reconstructed catch history back to 1935 when the population was assumed to be near to an unfished equilibrium.  Catch histories for some sectors were imputed from limited data.  For the first time in a Bocaccio assessment, recreational catch was included as in input to the model.  As in the previous work, this analysis indicates that Bocaccio exploitable stock biomass has declined significantly from the 1930s, with the steepest decline occurring from 1985 to 1995.  The rate of decline slowed after 1995.  While there is considerable uncertainty in estimating recent trends, there is no sign that the population has started to increase, and, more than likely, has continued to decline in the most recent decade.  Based on the reference case results, the median estimate of stock size relative to its unfished stock size (B₂₀₁₂/K) is 3.5%.  The median estimate of current abundance relative to B_msy (biomass at maximum sustainable yield) is 7.0% with 90% confidence limits of 2.9% and 18.2% leaving little or no likelihood that the stock is currently above the lower Precautionary Approach reference point of 0.4*B_msy, based on the reference case.  Current harvests are approximately equal to the estimate of replacement yield.  The impacts of alternative model assumptions from those used in the reference case were explored in 18 additional sensitivity runs but these results were similar to those of the reference case.  Long term biomass projections were made for the reference case and a selection of the sensitivity runs over 5, 20, and 60 year scenarios under varying fixed harvest assumptions from 0-200 t/y.  Results of the forecasts were presented relative to the DFO draft policy target references points of 0.4*B_msy and 0.8*B_msy.  While the Bayesian approach used in this assessment provides a formal mechanism to include uncertainty in model output (including predictions), managers, and stakeholders are advised that not all sources of uncertainty have been addressed and that it is likely that the true uncertainty is even greater than that presented herein.

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