Applying a flexible spline model to estimate functional maturity and spatio-temporal variability in aurora rockfish ( Se
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plying a flexible spline model to estimate functional maturity and spatio-temporal variability in aurora rockfish (Sebastes aurora) Melissa A. Head & Jason M. Cope & Sophie H. Wulfing
Received: 22 January 2020 / Accepted: 19 July 2020 / Published online: 28 August 2020 # This is a U.S. government work and not under copyright protection in the U.S.; foreign copyright protection may apply 2020
Abstract We outline a new flexible method for estimating maturity that incorporates skip spawning, which can lead to non-asymptotic behavior in the population maturity schedule. This new approach aids fisheries managers who seek to understand marine species’ responses to changing oceans. In an effort to assess shifts in maturity and spawning behavior of west coast groundfish, we used this new method to evaluate spatio-temporal trends in length at maturity, the annual reproductive cycle, and spawning behavior of aurora rockfish (Sebastes aurora). We estimated biological (presence of physiological maturity markers) and functional (potential spawners in a given year) maturity using a standard logistic and the new flexible spline model. The range in lengths at 50% maturity (biological and functional) slightly varied between the two methods (23.66–23.93 and 25.34–25.57 cm). We also investigated spatial trends in maturity and found ~ 2 cm difference in functional maturity between fish sampled north and south of Cape Mendocino, CA (26.22–26.48 and 24.38–24.74 cm). We demonstrate model sensitivity by updating the maturity estimates in the 2013 aurora rockfish stock assessment. Absolute, but not relative, M. A. Head (*) : J. M. Cope Fishery Resource Analysis and Monitoring Division, Northwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, 2725 Montlake Blvd East, Seattle, WA 98112, USA e-mail: [email protected] S. H. Wulfing Colorado College, Colorado Springs, CO, USA
spawning output, was sensitive to model choice, spatial resolution, and the updated data. This new flexible spline model can account for skip spawning, capturing potential spawners in a given year, and thus provides accurate measurements for spawning output models. Keywords Maturity ogive . Skip spawning . Sebastes . Functional maturity . Flexible non-asymptotic model . Spatio-temporal variability
Introduction Spatio-temporal trends in life history of marine fishes are understudied, despite their relative importance to sustainable management of marine resources (Keller et al. 2012; Gertseva et al. 2017). Many variables contribute to spatio-temporal differences in growth, maturation and other population indices, such as environmental conditions and variable fishing pressure throughout a species’ geographical distribution (Rose et al. 2001; Sharpe and Hendry 2009; Gertseva et al. 2017). In spite of this variability, marine fishes along the U.S. West Coast are primarily managed across expansive spatial areas, but key reproductive parameters in population models often come from small regional studies and/or l
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