Science Advisory Report 2009/040

Recovery Potential Assessment of Bocaccio in British Columbia waters

Summary

• The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) has assessed the bocaccio population in B.C. as Threatened. A final decision by the Government of Canada is required by December 2010. If the threatened listing is accepted, a Recovery Strategy will be required within two years from the date of acceptance.
• This document provides the scientific advice required for development of the Recovery Strategy. It follows the outline provided in the Revised Protocol for Conducting Recovery Potential Assessment (RPA) and is derived partly from a stock assessment on bocaccio reviewed by the Pacific Scientific Advice Research Committee (PSARC) in October 2008. The specific intent of this RPA is to predict the impact of future harvest levels on bocaccio abundance relative to attaining a target stock status. The stock status and forecasting advice are framed to be consistent with the current DFO policy on the Precautionary Approach (PA).
• Bocaccio are one of over 39 species of rockfish present in B.C. waters. Other vernacular names for bocaccio include rock salmon, salmon rockfish, Pacific red snapper, Pacific snapper, and Oregon snapper, however these names are shared with other species. Female bocaccio mature at about 7 years of age with a generation time of about 20 years. The population is assumed to be one designatable unit in B.C.
• Little is known about the distribution of young bocaccio in B.C. waters although they have been captured in nearshore sub-tidal depths. California studies indicate that young of the year reside near the surface for a few months then settle to the littoral and demersal habitat in late spring and summer. Most of the late stage juveniles and adult specimens are caught over bottom depths of 60-340 m on the continental shelf. Most bocaccio die if released after capture. Bocaccio does not appear to exhibit “residence requirements” as defined in the SARA legislation.
• A coastwide assessment of bocaccio was conducted using a Bayesian surplus production model that was fitted to six fishery-independent surveys, commercial bottom trawl CPUE and a catch reconstruction starting in the 1930s. The assessment was reviewed by PSARC in October 2008. This document includes analytical revisions to the model formulation causing a recalculation of the main results. These are provided in this document.
• The overall long-term trend in the updated version has changed very little from the version presented to PSARC, with the biomass showing a progressive decline since the 1930s and the steepest decline occurring between 1985 and 1995. The estimates of stock status lie within the reference critical zone according to the DFO PA and the current absolute and relative status is estimated to be lower than when presented to PSARC. The mean and median estimates of 2008 biomass are now estimated to be 3,022 t and 2,324 t respectively, with the previous comparable estimates being 4,383 and 3,252 t. The updated posterior mean and median estimates of relative stock status (B08/BMSY) are 0.155 and 0.111 respectively, which were previously 0.229 and 0.166.
• Harvests in the commercial groundfish fisheries are assumed to be the major current source of human-induced mortality. Total catch in the 2007/2008 fishing year was 135 t and 17 t in the groundfish trawl and hook & line (HL) fisheries, respectively. These catches are incidental while targeting on other species. Landings and at-sea catches (retained and discarded) are monitored in all commercial groundfish fisheries with 100% coverage. There is negligible discarding of undersized fish. The catches of First Nations and recreational fisheries are unknown but likely relatively small.
• Catches in U.S. waters may have an impact on the population of bocaccio in B.C. waters, but the size of this impact is unknown. Recent U.S. assessments have indicated some rebuilding in U.S. waters.
• Given that bocaccio appear to be predominantly a semi-pelagic aggregating species with areas of highest density (for adults) along the edge of the continental shelf and they appear to be much reduced in abundance from pre-exploitation levels, we know of no basis for assuming that the current quantity of physical habitat is limiting abundance. However, recent unpublished information on observed declines in dissolved oxygen which appear to be correlated with apparent shifts in distribution of many groundfishes species to shallower depths may be a source of concern. These observations are preliminary and their longterm significance is unknown. There is no information available to suggest that bocaccio rockfish have residence requirements, as defined in SARA.
• Restricting commercial catches appears to be the most practical means at present to minimize harm to bocaccio in B.C. waters. How catch restrictions are implemented should be developed in consultation with industry.
• Recovery targets (i.e. target biomass, the time frame, and likelihood of reaching the target) must be developed through the consultation phase. A series of decision tables provided in the document give predictions of stock trends under several harvest rules under a range of modelling assumptions. These tables capture the relative trade-offs required over these dimensions.
• While the Bayesian approach used in the assessment provides a mechanism to include uncertainty in estimating the current status of the population, managers, and stakeholders are advised that not all sources of uncertainty have been addressed and the true uncertainty is even greater with the 20-y and 40-y forecasting adding even more uncertainty. These projections assume the population will respond to the future environment as it did to the past environment, an assumption which may not hold due to the effects of cyclical or longterm climate change and/or other external processes.
• Notwithstanding the uncertainty in the assessment and forecasts, short-term projections of 1 to 2 years predict that current commercial groundfish catches of about 150 t per year will not place the population in significant additional jeopardy, suggesting that it is not necessary to accelerate the time frame required to implement a Recovery Strategy and Action Plan (if required). However, longer term predictions based on the decision tables in this document suggest that a reduction in harvest from current levels is required to significantly increase the probability of a population increase.

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