| INSIGHTS TO ENVIRONMENTAL DRIVERS OF RECRUITMENT VARIABILITY IN ROCKFISHES FROM MODELS OF EARLY LIFE HISTORY DYNAMICS |
| BJORKSTEDT, ERIC, P., NOAA/NMFS and Department of Fisheries Biology, Humboldt State University, Telonicher Marine Lab, PO Box 690, Trinidad, CA, 95570, USA, Eric.Bjorkstedt@noaa.gov, Kathryn E. Crane, Department of Fisheries Biology, Humboldt State University, Telonicher Marine Lab, PO Box 690, Trinidad, CA, 95570, USA, Kathryn.Crane@humboldt.edu |
| Numerous economically and ecologically important rockfishes (Sebastes spp.) release their larvae into the plankton during the winter and early spring, a period normally associated with relatively low productivity, but recently appreciated as critically important for establishing the trajectory of annual productivity in the California Current. In these rockfishes, as for many marine fishes, year-class strength appears to be largely determined by survival through the larval and early juvenile stages. We have developed an individual-based model (IBM) for rockfish early life history that summarizes information from the literature and incorporates recent advances in our understanding of environmental influences on growth derived from analysis of otolith growth increments. Using this IBM to integrate the results from a coupled biological-physical model of the coastal ocean, we have examined the relationship between variability in environmental forcing and recruitment to several rockfish stocks from 1983 to 2010. Our models capture a substantial amount of variability in recruitment estimated in stock assessments, and successfully predict large year classes that were poorly detected in pre-recruitment surveys. Moreover, our models provide insight to possible mechanisms that determine recruitment success in these stocks. From the perspective of a match-mismatch of larval rockfish and prey production, recruitment success appears to depend strongly on the timing, intensity, and variability of local forcing, such as upwelling-relaxation events occuring during the winter, as well as the effects of remote forcing (e.g., El Nio events) that control how effectively upwelling enriches the plankton ecosystem. However, recruitment appears to be negatively related to the density of predatory zooplankton (or of planktivores attracted to stocks of larger zooplankton), leading to the hypothesis that recruitment depends also on ecosystem productivity during the preceding year. Our results support the need for year-round ecosystem observations for understanding recruitment of rockfishes and other species in coastal upwelling systems, and set the stage for enhancing existing models of larval transport and connectivity along the U.S. West Coast with predictions of individuals fates. |
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