Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 8279
Title: Evidence that summer jellyfish blooms impact Pacific Northwest salmon production
Author: J. J. Ruzicka, Elizabeth A. Daly, Richard D. Brodeur
Publication Year: 2016
Journal: Ecosphere
Volume: 74
Issue: 4
Pages: e01324
Keywords: salmon, coastal ecosystem, jellyfish, competition, ecological modeling,

Interannual variability of salmon (Oncorhynchus spp.) production in the northeast Pacific is understood to be driven by oceanographic variability and bottom-up processes affecting prey availability to juvenile salmon.  Scyphozoan jellyfish have an important role shaping the pathways of energy flow through pelagic food webs.  While jellyfish obtain high production rates and biomasses as major consumers of zooplankton production, they have few predators and may divert plankton production away from higher trophic levels.  Although jellyfish are planktivorous and juvenile coho (O. kisutch) and Chinook (O. tshawytscha) salmon are mainly piscivorous, they may be indirect competitors for plankton production.  Ecosystem model simulations suggest that among all trophic interactions within the Pacific Northwest coastal food web, juvenile salmon are particularly sensitive to jellyfish blooms, and that salmon production will be suppressed in years of high summer jellyfish biomass.  Pelagic surveys off Oregon and Washington (1999-2012) were used to examine the interannual relationship between salmon production and the dominant jellyfish species off the Pacific Northwest coast, the sea nettle Chrysaora fuscescens

There was a significant, negative correlation between sea nettle biomass and the strength of adult coho and Chinook salmon returns to the Columbia River.  Examination of spatial distributions across years showed a positive association between sea nettles and salmon.  Within individual years, significant differences between the distribution of sea nettles and yearling coho and Chinook salmon generally occurred during cooler ocean summers, perhaps due to the greater expanse of optimal salmon habitat resulting from more upwelling.  Whether the association is behavioral or a product of oceanographic processes, association enhances the opportunity for indirect competition.  Examination of feeding incidence in September showed that salmon stomachs were less full at locations with higher sea nettle biomass.

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Theme: Ecosystem approach to improve management of marine resources
Foci: Characterize ecological interactions (e.g. predation, competition, parasitism, disease, etc.) within and among species.
Provide scientific support for the implementation of ecosystem-based management