Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 4708
Title: Distribution of demersal fishes along the U.S. west coast (Canada to Mexico) in relation to spatial fishing closures (2003  2011)
Author: A. A. Keller, W. Waldo Wakefield, C. Whitmire, B. H. Horness, Marlene A. Bellman, K. L. Bosley
Publication Year: 2014
Journal: Marine Ecology Progress Series
Volume: 501
Pages: 169-190
Keywords: California Current System,demersal fishes,spatial fishing closure,rockfish conservation area

ABSTRACT: A temporally and spatially variable Rockfish Conservation Area (RCA) was established along the U.S. west coast in 2002 to protect long-lived rockfish stocks (Sebastes spp.) by restricting commercial trawling in regions where depleted stocks were most abundant. Since the RCA falls within the region sampled annually by the Northwest Fisheries Science Centers West Coast Groundfish Bottom Trawl Survey (32º302  48º102 N Lat.), we utilized data collected from 2003 to 2011 to evaluate the impact of the RCA on catch per unit effort (CPUE, kg ha-1), species richness, and size distribution of demersal fish. We compared catch and species richness among three management areas (continuously closed, periodically closed, and open to commercial bottom trawling) using analysis of covariance models that account for variability due to area, year, and depth. The most appropriate models for catch (35 species treated individually and aggregated into six subgroups) and species richness were selected using Akaikes information criteria (AIC). All of the best fit models were highly significant (P < 0.0001), explaining 3 to 76% of the variation in catch and the majority (19 of 35) included both area and depth. For 27 species and five subgroups of demersal fish, the mean CPUE (based on Tukeys multiple comparison test) was significantly greater within the area continuously closed to commercial bottom trawling relative to areas periodically closed or open. The most appropriate model for species richness included area and year and mean richness was greatest in the area continuously closed to commercial bottom trawling. Species-specific length composition distributions were calculated from subsampled individual lengths which were available for 31 species. Significant differences in length frequency distributions (Kolmogorov-Smirnov asymptotic test statistic, P < 0.001) were observed for these 31 demersal fish species, with a higher proportion of larger fish most often (~65%) present in areas continuously closed to commercial bottom trawling (20 of 31 species) relative to other areas. Our data suggest that the RCA is an effective management tool for conserving not only rockfish, but other demersal fish species. Although no increases in CPUE occurred over the time examined, both catch and species richness were greater in the closed portion of the RCA and a higher proportion of larger fish occurred there.

Full Text URL: doi: 10.3354/meps10674
Theme: Recovery, Rebuilding and Sustainability of Marine and Anadromous Species
Foci: Investigate ecological and socio-economic effects of alternative management strategies or governance structures.