2006 Volume 70 Issue 1 Pages 16-22
Statolith increment analysis was applied to 400 specimens of the Japanese common squid, Todarodes pacificus, in order to estimate ages and population structure. Samples were collected during June–November 2001 in the Japan Sea and the Okhotsk Sea off northern Hokkaido. Three groups having different hatching dates were detected. Squids that hatched in autumn–winter (Sep.–Feb., mainly late Nov.–middle Dec.) and in winter–spring (Dec.–Jun., mainly middle Feb.) occurred in the Japan Sea off northern Hokkaido during June–September and October–November, respectively. Squids that hatched in spring (Feb.–May, mainly early Apr.) occurred in the Okhotsk Sea off northern Hokkaido during October–November. During June–September, the squids that hatched in autumn–winter migrate northward to the Japan Sea off northern Hokkaido, and then they migrate southward from the area to the spawning ground. After that during October–November, the squids that hatched in winter–spring recruit and form the main population in the area. Based on the current results, two catch-peaks in the Japan Sea off northern Hokkaido and one catch-peak in the Okhotsk Sea off northern Hokkaido resulted from catching the three groups of the squid in the areas.
