琵琶湖南湖西岸域で操業される魷の漁撞における優先種の交代に関する一考察

摘要

Lake Biwa (35°15'N, 136°05'E) is Japan's largest body of freshwater where various fishing gears have long been operated for catching fish and other aquatic species. One major fishery in Lake Biwa is the small set-net fishery 'eri', which is designed to catch migratory species that tend to follow the shoreline of the lake. We report on a small set-net operated in the western part of the south-basin fishing ground of the lake. The daily catch data from 1991 to 2009 showed that the native species catch had been decreasing from 1996, and after 1996 onwards the invasive alien species catch had exceeded the native species catch. The catch species diversity index (δ) indicated a yearly decrease. The results suggest that the temporal and spatial distribution pattern of migrating species in a given area changes, and for the past 14 years, less native migratory species appear in the catch diversity.