Nippon Suisan Gakkaishi 78 (2), 230-240 (2012)

Growth of Chionoecetes japonicus females west of the Oki Islands, Sea of Japan

IKUKO YOSHO,1* TARO HIROSE2 AND SHIGERU SHIRAI3

1Japan Sea National Fisheries Research Institute, Fisheries Research Agency, Chuo, Niigata 951-8121, 2Marine Fisheries Research and Development Center, Fisheries Research Agency, Yokohama, Kanagawa 220-6115, 3Faculty of Bio-Industry, Tokyo University of Agriculture, Abashiri, Hokkaido 099-2493, Japan

To clarify the growth and bathymetric distribution of Chionoecetes japonicus females, we sampled them by a sledge net from the depth range of 200-2000 m west of the Oki Islands in the Sea of Japan, during every summer for 7 years (2005-2011). In 2005, there were two depth zones at which immature females were abundant at ≤1000 m and ≥1700 m deep, and of which the modes of carapace width were different. The size distribution pattern in following years suggested that the growth rates of these groups were different.

   We detected 5 different instars in immature and 2 instars in adult, and the mean size of each instar was estimated from the carapace width frequency by the Hasselblad method. The smallest instar was regarded as the 6th instar. Compared with the mean size of the same instar by depth, it was smaller at deeper depth in all the instars other than the 6th instar. This suggests that the growth per molt could be smaller at deeper depths in this study area. Moreover, the main instar at maturity molt (9th or 10th) may differ by depth.


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