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Research Document - 2000/089

Northern cod recruitment before, during and after the collapse.

By P.A. Shelton and D.E. Stansbury

Abstract

We show that clear recruitment signals are present in the research vessel and commercial catch at age data for northern cod from extension of jurisdiction to moratorium. There have been three main periods of strong recruitment, preceded and followed by brief periods of much lower recruitment. SPA provides good model fits to the first two pulses but is unable to reconcile survey and catch data with respect to the third pulse, under standard assumptions. In this research document we use a diagnostic formulation that estimates unaccounted for deaths in the early 1990s to evaluate recruitment before and during the collapse. We reconstruct a relative recruitment strength series for the post-collapse period from a number of indices using an iterative reweighting procedure. Recruitment has decreased with the decline in spawner biomass and has been particularly low since the collapse.

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