Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 7520
Title: The potential impact of time-variation in vital rates on fisheries management targets for marine fishes
Author: James T. Thorson, Cole C. Monnahan, Jason Cope
Publication Year: 2015
Journal: Fisheries Research
Volume: 169
Pages: 8-17
Keywords: time-varying parameters, nonstationary, fisheries management, life table, perturbation analysis, life history strategy,

 Fisheries scientists are increasingly concerned about changes in demographic rates caused by environmental change and fishing impacts.  However, there has been relatively little synthesis regarding the relative magnitude of variation in demographic parameters over time, or how fisheries management targets change following variation in demographic rates.  We therefore pursue two study goals.  First, we use a life table (based on age-structured assessment models) to explore the elasticity of fishing mortality, spawning biomass, and catch targets to changes in parameters representing growth, mortality, recruitment, and maturation rates, for either periodic (i.e., red snapper) or opportunistic (i.e., Pacific sardine) life histories.  Second, we conduct a preliminary review of published studies to determine the relative magnitude of changes in these parameters on approximately decadal time scales.  The elasticity analysis indicates that demographic changes can result in substantial variation in fisheries management targets, but that changes in juvenile mortality rates are particularly important for spawning biomass and catch targets while maturity and recruitment compensation are also important for fishing mortality targets.  The literature review indicates that all parameters have in some cases been documented to change over time, with mortality rates showing greatest changes over time.  We conclude by exhorting fisheries scientists to embark on a collaborative and multi-agency effort to identify and account for time-varying demographic rates in population models and fisheries management. 


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Theme: Recovery and rebuilding of marine and coastal species
Foci: Characterize the population biology of species, and develop and improve methods for predicting the status of populations.
Develop methods to use physiological, biological and behavioral information to predict population-level processes.