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Comparison of trawled vs untrawled mud seafloor assemblages of fishes.pdf

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Comparison of trawled vs untrawled mud seafloor assemblages of fishes

gy and Ecology 344 (2007) 23–34 /locate/jembeJournal of Experimental Marine BioloComparison of trawled vs untrawled mud seafloor assemblages of fishes and macroinvertebrates at Coquille Bank, Oregon Mark A. Hixon a,?, Brian N. Tissot b a Department of Zoology, Oregon State University, 3029 Cordley Hall, Corvallis, Oregon 97331-2914, USA b Program in Environmental Science and Regional Planning, Washington State University Vancouver, 14204 NE Salmon Creek Avenue, Vancouver, Washington 98686-9600 USA Received 13 September 2006; received in revised form 24 October 2006; accepted 18 December 2006Abstract We report the first quantitative comparison of trawled vs untrawled mud seafloor communities off the west coast of North America. Using a manned submersible, we ran visual transects at Coquille Bank, 25 km off the central coast of Oregon, USA, including six half-hour (mean length 1184 m) transects over mud seafloors 183–361 m deep. The shallowest transects were untrawled, whereas deeper transects were heavily trawled, as evidenced by extensive trawl-door tracks. Differences between trawled and untrawled seafloor assemblages were striking. We observed 23% more fish over untrawled compared to trawled seafloors, and recorded 27 fish species on untrawled bottoms, but only 19 species on trawled seafloors. Regarding benthic invertebrates, density of individuals was 6 times greater on untrawled compared to trawled bottoms. Nonetheless, we observed 11 taxa on trawled seafloors and only 6 taxa on untrawled bottoms. Principal components analysis (PCA) defined the untrawled assemblage as characterized by sea pens, ratfish, sablefish, ronquil, slender sole, and poacher. PCA defined the trawled assemblage as characterized by seastars, hermit crabs, bigfin eelpout, Dover sole, hagfish, and shortspine thornyhead. In untrawled areas, there was no correlation between sea-pen density and total fish density, whereas in trawled areas, there was a marginally inverse correlation between the d