Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 4357
Title: Using a recruitment-linked multispecies stock assessment model to estimate common trends in recruitment for US West Coast groundfishes
Author: James T. Thorson, I. J. Stewart, Ian G. Taylor, A. E. Punt
Publication Year: 2013
Journal: Marine Ecology Progress Series
Keywords: recruitment,stock-recruit relationship,meta-analysis,dynamic factor analysis,stock assessment

 Recruitment is highly variable in marine fishes, and is predicted for many species using a stock-recruit relationship that has little explanatory power.  Researchers have sought for decades to characterize environmental variables that are associated with cohort strength, and often use stock assessment model estimates of recruitment within regressions outside of the stock assessment to test hypothesized drivers of recruitment variability.  This practice is statistically questionable because it fails to acknowledge differences in the precision of recruitment estimates among species and years, as well as covariance between recruitment estimates within a given species.  As an alternative, we develop a statistically-rigorous method to estimate an index of cohort strength that is shared among several stocks while controlling for each single-species stock-recruit relationship.  This method simultaneously optimizes multiple Stock Synthesis assessment models with shared cohort strength parameters, and uses observation-level fishery data to appropriately propagate the precision and covariance of estimates of cohort strength.  The method is demonstrated using data for nine groundfish species off the U.S. West Coast, and estimates anomalously low recruitment between 2002 and 2007.  The impact of a shared index of cohort strength is demonstrated for a data-poor species, yelloweye rockfish (Sebastes ruberrimus), where it decreases the coefficient of variation for the estimate of recruitment in the most recent year by 35%.  The method can be applied to other fishery management regions, particularly where Stock Synthesis is already used to assess species, and presents a rigorous method to estimate associations in recruitment among species within a region. 



 We develop a generic method to estimate correlations among stocks in cohort strength (i.e. recruitment deviations) using the Stock Synthesis assessment platform.  This demonstrates depressed recruitment for groundfishes off the U.S. West Coast from approx. 2002-2007, and significantly increases precision of recruitment estimates for information-poor species including yelloweye rockfish.  

Theme: Recovery, Rebuilding and Sustainability of Marine and Anadromous Species
Foci: Develop methods to use physiological and biological information to predict population-level processes.
Describe the relationship among human activities and species stock status, recovery, rebuilding and sustainability.