Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 7431
Title: Spatial overlap between forage fishes and the large medusa Chrysaora fuscescens in the northern California Current region
Author: Richard D. Brodeur, Caren Barceló, Kelly L. Robinson, Elizabeth A. Daly, J. J. Ruzicka
Publication Year: 2014
Journal: Marine Ecology Progress Series
Volume: 510
Pages: 167-181
Keywords: scyphomedusae,spatial overlap,climate,planktivores,forage fish

As in many regions of the world, the shelf waters of the western United States have experienced large increases and high interannual variability in jellyfish populations. The northern California Current (NCC) is a productive upwelling zone that is home to large populations of medusae particularly during some years. Seasonal trawl surveys in the NCC since 1999 have documented a substantial biomass of jellyfish consisting primarily of one species, the sea nettle (Chrysaora fuscescens) with abundances generally peaking in late summer. Trophic overlap can be high in the NCC with planktivorous species such as Pacific sardines and herring that consume copepods and euphausiid eggs. In this study, we examine the spatial overlap and co-occurrence of C. fuscescens and Pacific herring (Clupea pallasi), northern anchovy (Engraulis mordax) and Pacific sardine (Sardinops sagax) in the NCC using spatial analyses tools to determine the species that have the potential to be most affected by high jellyfish biomass and the geographic areas in which these interactions are likely to occur. Significant spatial overlap of these jellyfish with these pelagic fishes occurred during certain months and years, although the results were highly variable. There was an overall negative relationship between the abundance of Chrysaora and the catch of the three forage fishes for both June and September. End-to-end food web models show that jellyfish have a greater potential to affect production of pelagic forage fishes than the reverse.

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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.
Assess ecosystem status and trends.