1Graduate School of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido 041-8611, 2Hokkaido National Fisheries Research Institute, Fisheries Research Agency, Kushiro, Hokkaido 085-0802, Japan
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 gammarids and cumaceans to crustacean decapods and ophiuroids (chiefly Ophiura 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.