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Research Document - 2011/012

Construction of an assessment model for the shrimp (Pandalus borealis) stock off Newfoundland and Labrador using a Bayesian production model, first approach

By C. Hvingel and D. Orr

Abstract

For Illustrative purposes stock status and management advice for the Northern Shrimp, Pandalus borealis, within Shrimp Fishing Area 6 (SFA6) off Newfoundland and Labrador was derived based on a logistic stock-recruitment model with a state-space structure and Bayesian inference. The fishery effect was modelled explicitly while other mortality was included in the parameter for the overall realised population growth rate, r, and habitat carrying capacity, K. The model included both process and observation error and synthesized information from input priors and three independent series of shrimp biomass indices and a catch series. This model produced reasonable simulations of the observed data. Model results were stated relative to a set of MSY (Maximum Sustainable Yield) reference points. The Precautionary Approach limits proposed for stock biomass (B) was Blim=0.3Bmsy and for fishing mortality Flim=1.7Fmsy. Estimated stock biomass increased from the mid 1990s until 2006 to levels above the optimum, Bmsy, after which it declined toward Bmsy. In 2009 there was a 75% probability that the stock biomass was above Bmsy and that fishing mortality was below the value that maximizes yield (Fmsy). There was a 0% risk that the resource was below Blim in 2009. The mode of the estimated distribution of maximum annual production surplus, available to the fishery (MSY) was at 75 ktons. However, this estimate had wide confidence limits. Future catch options of up to 50 ktons/yr are likely to maintain the stock at its current high level. However, catch options of 60 ktons/yr or higher are under the current low levels of cod predation not likely to drive the stock below optimum levels in the short term either.

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