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Assessing bottom structure influence on fish abundance in a marine hill by using conjointly acoustic survey and geographic information system


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ABSTRACT:  Acoustic survey and a geographic information system (GIS) were used conjointly to estimate the significance of bottom substrate to explain fish abundance distribution in the complex topography context of a marine hill. The survey was conducted in the Hachirigase hill, off south-western Honshu Island in the Sea of Japan. Analysis of acoustic data focused on a 10-m thick layer beginning at the bottom, assuming that bottom influence does not exceed this distance. Area backscattering strength (Sa) values were rescaled in order to reflect real differences before being analyzed. Results show that the influence of the different parameters taken into account (bottom depth, bottom substrate and water temperature) varies widely from one place to another. Bottom substrate is above all important in the zone located to the west of the peak. The kriging and stratification methods were applied to the Sa distribution for estimating the total Sa in the hill. Differences between results are discussed. Conjoint use of acoustic survey and GIS is an effective method for analyzing and estimating fish abundance distribution in a marine hill.