夏季の北海道太平洋沖陸棚斜面域におけるキチジの食性

Abstract

The food habits of kichiji rockfish Sebastolobus macrochir were studied off the Pacific coast of Hokkaido. Fish samples were collected with a bottom trawl net at depths of 300-1,000 m in the daytime in July 2001 and 2002. Benthic invertebrates were collected with a Smith-McIntyre grab and a sledge net in July-August 2002. The percentage of empty stomachs of S. macrochir was low particularly in fish - 150 mm SL, indicating active feeding during the summer. Dietary analysis was conducted using 897 fish (43-271 mm SL). The principal prey item changed from small crustaceans such as ganmarids and cumaceans to crustacean decapods and ophiuroids (chiefly Cphiura leptoctenia) with increase of fish length. Ophiuroids, which are probably the most abundant prey in this study area, became very important in the diets of S. macrochir with the growth of fish. In addition, ophiuroid feeders including S. macrochir are very low in biomass in this study area. Such a foraging strategy of S. macrochir seems to reduce the intra- and inter-specific competition for food.