Research Document - 2011/003

Updated reference point estimates for northern Gulf of St. Lawrence (3Pn4RS) cod (Gadus morhua) based on revised beginning of year weights at age

By D.E. Duplisea and A. Fréchet

Abstract

Reference points for northern Gulf of St Lawrence (nGSL) cod were updated from the estimates presented at the 2009 cod zonal assessment process held in St. John’s (Duplisea and Fréchet 2009) owing to recent changes to the weight at age vector used for the calculation of spawning stock biomass (SSB). The new weight at age vector are based mostly on surveys corrected to January of each year rather than the weight age vector from the commercial fishery. The result of this change is that weight at age used for SSB calculation has decreased in all age classes though this does not affect abundance at age. Consequently, the previous estimate for the limit reference point declined from 140,000 t to 116,000 t and the upper stock reference point based on the recruitment plateau decreased from 200,000 t to 180,000 t. It is emphasised that changes to reference points here are mostly due to rescaling SSB and though it may change the perception of stock size, the actual abundance of fish in the water did not change in the VPA. Because the commercial weight at age vector is still used for TAC calculation and risk analysis, these are unaffected by the change in weight at age vector for SSB calculation.

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