Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 1161
Title: Variations in Eastern North Pacific Demersal Fish Biomass Based on The U.S. West Coast Groundfish Bottom Trawl Survey (2003-2010)
Author: Aimee Keller, J. R. Wallace, B. H. Horness, O. S. Hamel, I. J. Stewart
Publication Year: 2012
Journal: Fishery Bulletin
Volume: 110
Pages: 63-80

In response to declining biomass of Northeast Pacific groundfish in the late 1990s and to improve the scientific basis for management of the fishery, the Northwest Fisheries Science Center standardized and enhanced their annual bottom trawl survey in 2003. The survey was expanded to include the entire area along the U.S. West Coast at depths of 55–1280 m. Coast-wide biomass and species richness significantly decreased during the first eight years (2003–2010) of this fishery-independent survey. We observed an overall tendency towards declining biomass for 62 dominant taxa combined (fishery target and non-target species) and four of seven subgroups (including cartilaginous fish, flatfishes, shelf rockfishes, and other shelf species), despite increasing or variable biomass trends in individual species. These decreases occurred during a period of reduced catch for groundfish along the shelf and upper slope regions relative to historical rates. We utilized information from multiple stock assessments to aggregate species into three groups: with or without large recruitment in 1999 or unknown recruitment level. For each group, we evaluated if declining biomass was primarily related to depletion (using year as a proxy) or environmental factors (i.e., variation in the Pacific Decadal Oscillation). Based on Akaike’s Information Criterion, changes in aggregate biomass for species with strong recruitment were more closely related to year while those with no strong recruitment were more closely related to climate. The significant decline in biomass for species without strong recruitment confirms that factors other than depletion of the exceptional 1999 year class may be responsible for the observed decrease in biomass along the U.S. West Coast.