1Graduate School of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido 041-8611, 2Hokkaido National Fisheries Research Institute, Fisheries Research Agency, Kushiro, Hokkaido 085-0802, 3Faculty of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido 041-8611, Japan
The spatial distribution patterns and nutritional status of the kichiji rockfish Sebastolobus macrochir were investigated off the Pacific coast of Hokkaido during the summer of 2001-2004. Fish≤100 mm SL were chiefly distributed at depths of 550-750 m off the southeastern area of Cape Erimo where their principal prey, gammarid amphipods, were abundant. The 101-150 mm SL fish were concentrated in shallow areas where their principal prey, the decapod Neocrangon communis, was abundant. Conversely, fish≥151 mm SL were observed to utilize various prey items and were widely distributed in the study area, suggesting a foraging strategy to reduce the intra- and inter-specific competition for food and to obtain food efficiently. The condition factor and hepatosomatic index of S. macrochir tended to decrease with increased depth. Given that the principal prey of S. macrochir ranged from decapods (high energy content) to ophiuroids (low energy content) with increased depth, the variation in the nutritional status of fish could be related to differences in the energy content of their prey. Despite feeding on prey items with a relatively high energy content, the nutritional status of 101-150 mm SL fish was low. This is probably due to the fact that the fish in this size class grow rapidly.