Proceedings 2011/074

Proceedings of the Pacific Region Science Advisory Process on Pacific ocean perch in Queen Charlotte Sound, British Columbia; November 24, 2010

Chairperson: G. Workman

Summary

A regional advisory process meeting was held November 24, 2010 in Nanaimo (BC) to conduct a science peer review of the status of Pacific ocean perch (Sebastes alutus) in Queen Charlotte Sound, British Columbia. The science review was conducted in response to a request from DFO Fisheries and Aquaculture Management (FAM) for advice regarding the current stock status of Pacific ocean perch (POP) in Groundfish management areas 5AB and 5CD. Advice was requested on recommended limit reference point (LRP), upper stock reference point (USR) and target reference point (TRP), and the supporting rationale for their application to management of the POP stock in Queen Charlotte Sound. Harvest options were requested in the form of decision tables that summarize the expected effects of a range of catches relative to unfished stock size, current stock size and the future stock trajectory. Additional information needed to implement ecosystem-based fisheries management consistent with Sustainable Fisheries Framework (SFF) was also requested.

The Participants reviewed a working paper that described the development of an age and sex-structured catch at age model which was applied to the available data for POP in Queen Charlotte Sound. Four hypotheses distinguished by values of stock-recruitment steepness and natural mortality were evaluated using the model. Two hypotheses where steepness was freely estimated were (i) accepted as the basis for harvest advice, (ii) produced stock reconstructions with similar trends, and (iii) provided different characterizations of current stock status with respect to B_MSY-based reference points. The median posterior female spawning biomass at the beginning of 2011 is estimated to be 0.26 (0.12 to 0.43) when natural mortality is freely estimated and 0.14 (0.08 to 0.24) of the unfished equilibrium level when natural mortality is fixed at 0.06 (numbers in brackets denote the 2.5^th and 97.5^th percentiles of the posterior distribution of female spawning biomass). Estimates of annual exploitation rates have increased since the 1980s and are approaching, or have reached, the historic high levels associated with large catches by foreign fleets that occurred when the stock showed significant depletion in the late 1960s and 1970s. The exploitation rate in 2010 is estimated to range from 0.04-0.15, or 0.09-0.22, depending on the values of steepness and natural mortality. Following an increase in the stock biomass in the mid to late 1980s, the POP stock in Queen Charlotte Sound declined to historic lows by 2006/07 and has since increased slightly. Advice on future harvest is provided in the form of decision tables that show the probability of female spawning biomass, Bt, exceeding 0.4B_MSY, 0.8B_MSY, and B_MSY in each year of a five-year projection from 2011 to 2016.

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