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Marine Ecology Progress Series

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MEPS 634:159-173 (2020)  -  DOI: https://doi.org/10.3354/meps13185

California Current seascape influences juvenile salmon foraging ecology at multiple scales

Megan C. Sabal1,*, Elliott L. Hazen2, Steven J. Bograd2, R. Bruce MacFarlane3, Isaac D. Schroeder2,4, Sean A. Hayes5, Jeffrey A. Harding3, Kylie L. Scales2,4,6, Peter I. Miller7, Arnold J. Ammann3, Brian K. Wells3

1University of California Santa Cruz, Department of Ecology and Evolutionary Biology, Santa Cruz, CA 95060, USA
2Environmental Research Division, Southwest Fisheries Science Center, National Marine Fisheries Service, NOAA, Monterey, CA 93940, USA
3Southwest Fisheries Science Center, National Marine Fisheries Service, NOAA, Santa Cruz, CA 95060, USA
4Institute of Marine Sciences, University of California Santa Cruz, Santa Cruz, CA 95064, USA
5Northeast Fisheries Science Center, National Marine Fisheries Service, NOAA, Woods Hole, MA 02543, USA
6Global Change Ecology Research Group, School of Science and Engineering, University of the Sunshine Coast, Maroochydore, QLD 4556, Australia
7Remote Sensing Group, Plymouth Marine Laboratory, Plymouth PL1 3DH, UK
*Corresponding author:

ABSTRACT: Juvenile salmon Oncorhynchus spp. experience variable mortality rates during their first few months in the ocean, and high growth during this period is critical to minimize size-selective predation. Examining links between the physical environment and foraging ecology is important to understand mechanisms that drive growth. These mechanisms are complex and include interactions among the physical environment, forage availability, bioenergetics, and salmon foraging behavior. Our objectives were to explore how seascape features (biological and physical) influence juvenile Chinook salmon O. tshawytscha foraging at annual and feeding-event scales in the California Current Ecosystem. We demonstrate that forage abundance was the most influential determinant of mean salmon stomach fullness at the annual scale, while at the feeding-event scale, fullness increased with greater cumulative upwelling during the 10 d prior and at closer distances to thermal fronts. Upwelling promotes nutrient enrichment and productivity, while fronts concentrate organisms, likely resulting in available prey to salmon and increased stomach fullness. Salmon were also more likely to consume krill when there was high prior upwelling, and switched to non-krill invertebrates (i.e. amphipods, decapods, copepods) in weaker upwelling conditions. As salmon size increased from 72-250 mm, salmon were more likely to consume fish, equal amounts of krill, and fewer non-krill invertebrates. Broad seascape processes determined overall prey availability and fullness in a given year, while fine- and meso-scale processes influenced local accessibility of prey to individual salmon. Therefore, processes occurring at multiple scales will influence how marine organisms respond to changing environments.


KEY WORDS: Salmon diets · Fullness · Krill · Upwelling · Fronts · Retention


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Cite this article as: Sabal MC, Hazen EL, Bograd SJ, MacFarlane RB and others (2020) California Current seascape influences juvenile salmon foraging ecology at multiple scales. Mar Ecol Prog Ser 634:159-173. https://doi.org/10.3354/meps13185

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