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A multi-model approach to understanding the role of Pacific sardine in the California Current food web

Isaac C. Kaplan1,*, Tessa B. Francis2, André E. Punt3, Laura E. Koehn3, Enrique Curchitser4, Felipe Hurtado-Ferro3, Kelli F. Johnson3, Salvador E. Lluch-Cota5, William J. Sydeman6, Timothy E. Essington3, Nathan Taylor7, Kirstin Holsman8, Alec D. MacCall6, Phillip S. Levin9

1Conservation Biology Division, Northwest Fisheries Science Center, National Marine Fisheries Service, NOAA, 2725 Montlake Blvd E, Seattle, WA 98112, USA
2University of Washington Tacoma, Puget Sound Institute, Tacoma, WA 98421, USA
3School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA 98195-5020, USA
4Department of Environmental Sciences, Rutgers University, 14 College Farm Road, Room 243, New Brunswick, NJ 08901, USA
5Centro de Investigaciones Biológicas del Noroeste, S.C., 23096 La Paz, BCS, Mexico
6Farallon Institute, 101 H Street, Suite Q, Petaluma, CA 94952, USA
7Pacific Biological Station, Fisheries and Oceans Canada, 3190 Hammond Bay Rd, Nanaimo, BC V9T 6N7, Canada
8Alaska Fisheries Science Center, NOAA Fisheries, 7600 Sand Point Way NE, Building 4, Seattle, WA 98115, USA
9School of Environmental & Forest Sciences, University of Washington, Box 351200, Seattle, WA 98195, USA
*Corresponding author:

ABSTRACT: We develop a multi-model approach to explore how abundance of a forage fish (Pacific sardine Sardinops sagax) impacts the ecosystem and predators in the California Current, a region where sardine and anchovy Engraulis mordax have recently declined to less than 10% of contemporary peak abundances. We developed or improved applications of 3 ecosystem modeling approaches: Ecopath, Model of Intermediate Complexity for Ecosystem assessment (MICE), and Atlantis. We also used Ecopath diets to predict impacts to predators using a statistical generalization of the dynamic Ecosim model (Predator Response to the Exploitation of Prey [PREP]). Models that included brown pelican Pelecanus occidentalis at the species level (MICE and Ecopath/PREP) both predict moderate to high vulnerability of brown pelicans to low sardine abundance. This vulnerability arises because sardine comprises a large fraction of their diet, and because other important prey (anchovy) also exhibit large population fluctuations. Two of the ecosystem models (MICE and Atlantis) suggest that California sea lions Zalophus californianus exhibit relatively minor responses to sardine depletion, due to having broader diets and lower reliance on another fluctuating species, anchovy. On the other hand, Ecopath/PREP suggests that sardine declines will have a stronger impact on California sea lions. This discrepancy may in part reflect structural differences in the models: Atlantis and MICE explicitly represent density dependence and age-structure, which can mitigate effects of prey depletion in these models. Future work should identify fisheries management strategies that are robust to uncertainties within and among models, rather than relying on single models to assess ecosystem impacts of management and forage fish abundance.

KEY WORDS: Forage fish · Pacific sardine · California Current · Ecosystem model · California sea lion · Brown pelican · Multi-model approach

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Cite this article as: Kaplan IC, Francis TB, Punt AE, Koehn LE, Curchitser E, Hurtado-Ferro F, Johnson KF, Lluch-Cota SE, Sydeman WJ, Essington TE, Taylor N, Holsman K, MacCall AD, Levin PS(2018) A multi-model approach to understanding the role of Pacific sardine in the California Current food web. Mar Ecol Prog Ser

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