Evaluation of impacts of bottom fishing on demersal habitats: A case study off the Pacific coast of north-eastern Japan

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Physical disturbance of the seafloor induced by bottom trawling is of increasing concern from the viewpoints of ecosystem conservation and sustainable fishery. We developed a method for evaluating the impacts of several kinds of trawl gears on the different seafloor habitats using bathymetry and sediment data and scientific survey data off the Pacific coast of north-eastern Japan. Ten types of habitats were classified by the cluster analysis applied to seafloor bathymetry, topography, and sediment hardness over the study area. Our mapping of these habitats demonstrated that the intensity of bottom fishing activities on the seafloor was different among habitat types and related to the abundance of commercial species living in each habitat. The ecological influences of fishing on these habitats were examined by focusing on the changes in demersal species diversity and biomass detected through scientific surveys. A decline in species diversity was more evident in the habitat types with complex topography and hard sediment in the intensely trawled areas. Comparison of fishing gear suggested that the otter trawl may be the most influential owing to the significant change in the demersal ecosystem.