Research Document - 2009/055

Stock assessment for bocaccio (Sebastes paucispinis) in British Columbia waters

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

Abstract

This document provides a stock assessment for bocaccio in B.C. waters. Results of the work are intended to serve as advice over the short term to managers and stakeholders on stock status, and likely impacts of different harvest options. As such, it also provides the scientific advice required to develop a Recovery Strategy should this be deemed necessary. A Bayesian Schaefer surplus production model was used owing to an insufficient time series of age-structured data and lack of information on fishery vulnerability at size or age in the fisheries. It was fitted to one fishery dependent and six fishery independent stock biomass trend indices, and a reconstructed catch history back to 1935 when the population was assumed to be near to an unfished equilibrium. Some of the catch histories data were imputed from limited data. Informative Bayesian priors were used when estimating the survey proportionality constants, based in part on interviews with experienced fishermen. The reference run indicates a current stock size of about 3,000-5,000 t, with the stock estimated to lie between 10-15% of unfished stock size^{Footnote 1}. The impacts on current stock status of alternative model assumptions to those made in the reference case were explored in 31 runs. Long term biomass projections were made for the reference case and a selection of the sensitivity runs over 5, 20, and 40 year scenarios under varying fixed harvest assumptions. 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. These projections are shown as harvest tables for the reference set of assumptions as well as two additional scenarios which assume either a lower or higher estimate of productivity (r). 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 here.

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