A fully coupled ecosystem model to predict the foraging ecology of apex predators in the California Current

Abstract

Results from a fully coupled end-to-end ecosystem model for the California Current Large Marine Ecosystem are used to describe the impact of environmental variability and prey availability on the foraging ecology of its most abundant apex predator, the California sea lion Zalophus californianus. The ecosystem model consists of a biogeochemical submodel embedded in a regional ocean circulation submodel, both coupled with a multi-species individual-based submodel for forage fish (sardine and anchovy) and California sea lions. Sardine and anchovy are explicitly represented in the model as they are commonly found in the diet of sea lions and exhibit significant interannual and decadal variability in population abundances that reflect variations in their environment and lower trophic level prey. Output from a 20 yr run (1989−2008) of the model demonstrates how different physical and biological processes control habitat utilization and foraging success of California sea lions on interannual time scales, with the dominant modes of variability linked to sardine abundance and coastal upwelling intensity. The results also illustrate how variability in environmental conditions, forage fish distribution, and prey assemblage affect sea lion feeding success. While specifically focusing on the foraging ecology of sea lions, the modeling framework has the ability to provide a more complete understanding of the physical and biological mechanisms impacting trophic interactions in the California Current, or other regions where similar fully coupled ecosystem models may be implemented. KEY WORDS: Ecosystem model · Foraging ecology · California Current · Upwelling · Sea lions · Marine predators · Zalophus californianus Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 556: [273][274][275][276][277][278][279][280][281][282][283][284][285] 2016 In coastal upwelling regions such as the California Current Large Marine Ecosystem (CCLME), small pelagic forage fish (e.g. sardine and anchovy) constitute a significant part of the diet of apex predators. Be cause the variability in abundance and distribution of small pelagic fish reflects spatial and temporal changes in their environment (Bakun 2006, Field et al. 2006, the foraging ecology of their predators is also expected to depend on the fundamental processes regulating ocean conditions and lower trophic level production. Environmental variability in the CCLME is seasonally tied to the coastal upwelling of cool, nutrient-rich waters in response to prevailing alongshore winds, leading to elevated levels of new primary production along the majority of the US west coast. The region between the coastal upwelling zone and the offshore oligotrophic waters of the North Pacific subtropical gyre (i.e. 100 to 300 km from the coast) is known as the California Current transition zone (CCTZ;Brink & Cowles 1991), and is primarily influenced by mesoscale processes and wind stress curl (Kosro et al. 1991). Physical and biological differences bet...

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

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