1Hokkaido Kushiro Fisheries Experimental Station, Kushiro, Hokkaido 085-0024, 2Hokkaido Central Fisheries Experimental Station, Yoichi, Hokkaido 046-8555, 3Japan Sea National Fisheries Research Institute, Fisheries Research Agency, Niigata 951-8121, Japan
Statolith increment analysis was applied to 1,421 specimens of the Japanese common squid, Todarodes pacificus, to estimate the age and hatching date. Samples were collected during May-November in 2001 and 2002 in the waters around Hokkaido. Two hatching groups were observed in waters around Hokkaido: November- to December-hatched T. pacificus and February- to May-hatched T. pacificus. During May-September, November- and December-hatched squid predominated in the Sea of Japan off Hokkaido and in waters off southern Hokkaido. Squid that hatched in February-May were predominant in waters off southern Hokkaido and the Pacific coast off eastern Hokkaido during August-October, and during October-November in the Okhotsk coast off Hokkaido and the Sea of Japan off Hokkaido. It was found that between August and September, both hatching groups occurred in waters off southern Hokkaido.