The spatial distribution patterns and nutritional status of the kichiji rockˆsh Sebastolobus macrochir were investigated oŠ the Paciˆc coast of Hokkaido during the summer of 2001 2004. Fish100 mm SL were chie‰y distributed at depths of 550 750 m oŠ the southeastern area of Cape Erimo where their principal prey, gammarid amphipods, were abundant. The 101 150 mm SLˆsh were concentrated in shallow areas where their principal prey, the decapod Neocrangon communis, was abundant. Conversely,ˆsh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-speciˆc competition for food and to obtain food e‹ciently. 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 ofˆsh could be related to diŠerences 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 SLˆsh was low. This is probably due to the fact that theˆsh in this size class grow rapidly.

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 300-1,000m 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 ≤150mm SL, indicating active feeding during the summer. Dietary analysis was conducted using 897 fish (43-271mm 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

No abstract

We developed an age determination method for Ezo abalone Haliotis discus hannai using the internal growth rings in the cross-section of the inner lip shell. A laboratory experiment showed that 1-year-old juveniles had one internal growth ring that was deposited during the season of lowest seawater temperature. Tagged juveniles (2 years old) were released into their natural habitat and recaptured after 2 5 years from the date of release. The recaptured individuals (n＝3) had the same number of internal growth rings as their age in addition to one disturbance ring. Results of stable oxygen isotope analysis on the shell cross-sections conˆrmed that the growth rings were deposited between winter and spring when the temperature decreased below 7°C. Furthermore, the disturbance rings that were observed only in the released individuals were formed at the time of release into the natural habitat. Comparing the validity of the age determination method developed in this study with the conventional burning shell method, the age estimated by the conventional method was less than that by the present method for 8-year-old abalone. Age determination using internal growth rings is more accurate than the conventional method, leading to diŠerences of 1 2 years in estimates.