Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 9081
Title: A multi-model approach to understanding the role of Pacific sardine in the California Current food web
Author: I. C. Kaplan, T B Francis, A. E. Punt, Laura E. Koehn, Enrique N. Curchitser, Felipe Hurtado-Ferro, Kelli F. Johnson, Salvador Lluch-Cota, William J. Sydeman, T. E. Essington, Nathan G. Taylor, K. K. Holsman, A. D. MacCall, P. S. Levin
Publication Year: 2018
Journal: Marine Ecology Progress Series
Abstract:

A central tradeoff in ecosystem-based fishery management is between harvest of forage fish and potential impacts on dependent predators.  Here we develop a multi-model approach to explore how sardine Sardinops sagax abundance 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 their peak abundances. We developed or improved applications of three ecosystem modeling approaches: Ecopath, MICE, and Atlantis; we also used static Ecopath diets to predict impacts to predators using a statistical generalization of the dynamic Ecosim model (PREP). Results from both ecosystem models for which we have brown pelicans Pelecanus occidentalis modeled at the species level (MICE and Ecopath/PREP) emphasize the vulnerability of brown pelicans to low sardine abundance due to diets that are high in sardines and another species with high variability, anchovy. Two of our ecosystem models (MICE and Atlantis) suggest that California sea lions Zalophus californianus should exhibit relatively minor responses to sardine depletion, due to having broader diets and lower reliance on anchovy. On the other hand, Ecopath/PREP suggests that sardine declines will have a strong impact on California sea lions. This discrepancy reflects structural differences in the models: weaker responses in Atlantis and MICE are likely attributable to the explicit representation of density dependence and age-structure. We emphasize that next steps involve finding fisheries management strategies that are robust to uncertainties in model structure, rather than relying on single models to assess ecosystem impacts of management actions and forage fish abundance.

Foci: Provide scientific support for setting annual catch limits and measure results of annual catch limit implementation