Spatial distribution patterns and nutritional status of kichiji rockfish Sebastolobus macrochir in summer on the continental slope off the Pacific coast of Hokkaido, Japan

Abstract

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.

Growth changes in bighand thornyhead Sebastolobus�macrochir off the Pacific coast of northern Honshu, Japan

“…The nutritive value of crustaceans is two-to fourfold higher than that of ophiuroids. 15 These results suggest that the main prey items of bighand thornyhead changed from a high nutrition diet in the 1950s to a low nutrition diet in the 2000s.…”

“…In the spring/summer of the 2000s, the frequency of crustaceans (especially benthic shrimps) decreased, while ophiuroids increased in fish stomachs. The nutritive value of crustaceans is two‐ to fourfold higher than that of ophiuroids 15 . These results suggest that the main prey items of bighand thornyhead changed from a high nutrition diet in the 1950s to a low nutrition diet in the 2000s.…”

Annual changes in distribution depths of bighand thornyhead Sebastolobus macrochir off the Pacific coast of northern Honshu, Japan

“…Shortspine S. alascanus and longspine thornyhead S. altivelis showed significant positive size–depth correlations (bigger–deeper) off southern California 14 . In bighand thornyhead, distribution depths of small (≤10 cm SL) and large size fish (≥20 cm SL) were deeper than that of medium size fish off the Pacific coast of Hokkaido, northern Japan, in 2001–2004, suggesting that bighand thornyhead does not show a bigger–deeper trend 15 . However, it is possible that the size–depth relationship is variable with change in fish biomass.…”

Spatiotemporal variations in nutritional status and feeding habits of immature female bighand thornyhead Sebastolobus macrochir off the Pacific coast of northern Honshu, Japan

“…In southern Tohoku, the %IRI of squids, euphausiids, benthic shrimps, and/or fishes was high in shallower waters. The nutritional value of crustaceans is two-to fourfold higher than ophiuroids or polychaetes, and fish is considered the best quality food item for bighand thornyhead [9]. Firefly squid [18] and benthic shrimps [4] are also an important food item for bighand thornyhead in the Tohoku area.…”

“…Thus, in the Tohoku area, it is probable that small bighand thornyhead are potentially in poorer condition and that specimens distributed in deeper waters have a lower nutritional status. The nutritional status and feeding habits of bighand thornyhead have been studied off the Pacific coast of Hokkaido Island, northern Japan [8,9], but not in the Tohoku area. Therefore, the present study examines the spatiotemporal variations in nutritional status and feeding habits of immature bighand thornyhead in the Tohoku area and discusses the effect on growth, due to the variations in nutritional status and feeding habits, produced by distributional changes.…”