Research Document - 2010/086

Atlantic Halibut on the Scotian Shelf and Southern Grand Banks (NAFO Divisions 3NOPs4VWX5Zc) – Industry/DFO Longline Survey and Tagging Results to 2009

By M.K. Trzcinski, S.L. Armsworthy, and S. Wilson

Abstract

Four catch rate analyses of the halibut survey show recent increases in the exploitable population of Northwest Atlantic Fisheries Organization (NAFO) divisions 3NOPs4VWX5Zc Atlantic halibut, with the largest increase in 2009. Standardizing the catch rate with a general linear model (GLM) is considered the most credible analysis. When vessels effects are accounted for, there is a significant positive trend in catch rates over the past 12 years. Recruitment has increased over the past five years in the halibut survey, has declined in the research vessel (RV) survey over the last two years, but remains above the long term mean. This recruitment is starting to show up as exploitable biomass, and the 2009 catch rates in the halibut survey are the highest on record. The 2008 exploitation rate of the exploitable biomass (>81cm) was estimated to be 15.0% (90% Confidence Interval (CI): 13.3–16.8%) based on the tagging results, although this value is expected to increase as more tags are sent in. As noted in Trzcinski et al. (2009), this exploitation rate is higher than natural mortality (10%) and F0.1 (9%), and it is not known whether this rate is sustainable. The surplus production to catch ratio is expected to remain approximately the same as in 2008 (3:1), and the longer-term consequences of utilizing this ratio should be evaluated in the context of stock management objectives, reference points, and a risk management framework. Based on the abundance indices presented here, there is no basis to advise on a change in harvest level in 2010/2011.

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