Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 9128
Title: Environmental conditions and prey-switching by a seabird predator impact juvenile salmon survival
Author: Brian K. Wells, Jarrod A. Santora, Mark J. Henderson, Pete Warzybok, Jaime Jahncke, Russel W. Bradley, David D. Huff, Isaac D. Schroeder, Peter Nelson, John C. Field, D. G. Ainley
Publication Year: 2017
Journal: Journal of Marine Systems
Volume: 174
Pages: 54-63
DOI: 10.1016/j.jmarsys.2017.05.008
Keywords: California Current,Chinook salmon,Common murre,ecosystems,forage fish,inland water environment

Due to spatio-temporal variability of lower trophic-level productivity along the
California Current ecosystem (CCE), predators must be capable of switching prey or
foraging areas in response to changes in environmental conditions and available
forage. The Gulf of the Farallones in central California represents a biodiversity
hotspot and contains the largest common murre (Uria aalge) colonies along the CCE.
During spring, one of the West Coast’s most important Chinook salmon
(Oncorhynchus tshawytscha) populations out-migrates into the Gulf of the
Farallones. We quantify the effect of predation on juvenile Chinook salmon
associated with ecosystem-level variability by integrating long-term time series of
environmental conditions (upwelling, river discharge), forage species abundance
within central CCE, and population size, at-sea distribution, and diet of the common
murre. Our results demonstrate common murres typically forage in the vicinity of
their offshore breeding sites, but in years in which their primary prey, pelagic
young-of-year rockfish (Sebastes spp.), are less available they forage for adult
northern anchovies (Engraulis mordax) nearshore. Incidentally, while foraging
inshore, common murre consumption of out-migrating juvenile Chinook salmon,
which are collocated with northern anchovy, increases and population survival of
the salmon is significantly reduced. Results support earlier findings that show
timing and strength of upwelling, and the resultant forage fish assemblage, is related
to Chinook salmon recruitment variability in the CCE, but we extend those results by
demonstrating the significance of top-down impacts associated with these bottom up
dynamics. Our results demonstrate the complexity of ecosystem interactions and impacts between higher trophic-level predators and their prey, complexities
necessary to quantify in order to parameterize ecosystem models and evaluate
likely outcomes of ecosystem management options.

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Theme: Ecosystem approach to improve management of marine resources
Foci: Characterize the interaction between marine, freshwater and terrestrial ecosystem components.
Characterize ecological interactions (e.g. predation, competition, parasitism, disease, etc.) within and among species.
Official Citation:

Wells, B. K., J. A. Santora, M. J. Henderson, P. Warzybok, J. Jahncke, R. W. Bradley, D. D. Huff, I. D. Schroeder, P. Nelson, J. C. Field, and D. G. Ainley. 2017. Environmental conditions and prey-switching by a seabird predator impact juvenile salmon survival. Journal of Marine Systems 174:54-63.