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SSC Workshop on Use of Stock-Recruitment Relationships in Stock Assessments

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At the North Pacific Fishery Management Council’s December 2011 meeting, the Scientific and Statistical Committee (SSC) chose stock-recruitment (SR) issues as its topic for its upcoming workshop, which was held 1 February 2012, in conjunction with the February SSC meeting.  Many Status of Stocks and Multispecies Assessments (SSMA) program staff and collaborators provided presentations on relevant topics.  Megan Stachura (graduate student at the University of Washington, (UW)), Cody Szuwalski (UW), and Teresa A’mar considered analytical approaches to address regime shifts in stock production. These presentations applied statistical methods to identify shifts in recruitment and evaluated the implications of shifting time frames on harvest control strategies.  Jim Ianelli and Tom Wilderbuer introduced approaches in which variables representing environmental forcing are incorporated into the SR relationship.  Martin Dorn, Grant Thompson, and Jim Ianelli showed different approaches to incorporate spawner recruitment relationships into stock assessments.  Martin Dorn noted that west coast assessment scientists  estimate the  steepness parameter of the stock recruitment relationship either with a prior based on a meta analysis of groundfish stock recruitment, or by fixing steepness at the mean of the meta analysis. Grant Thompson introduced a statistical method to estimate mean recruitment and sigma R.  Jim Ianelli provided an example where he conditioned the spawner-recruit parameters on the basis of the assumption that F35% was equal to FMSY.

Workshop participants discussed the criteria needed to transition a stock to Tier 1 and commented that the posterior distribution function of FMSY should incorporate several sources of error in growth, natural mortality, selectivity, and the SR relationship.  The SSC and Plan Team members discussed timelines to continue research on this topic.  The SSC recommended, and the Plan Team concurred, that the next step would be to hold a workshop to develop guidelines on how to accommodate environmental changes in the SR relationship into the calculation of biological reference points and how to model environmental forcing in stock projection models. This workshop will be held at the Center on 4-5 April 2012.

By Anne B. Hollowed

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