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known distribution. Hence, the region indicated byClass 5 could be a fishing area for both autumn andwinter spawning groups. Abundance of T. pacificus isdetermined by recruitment during the autumn andwinter spawning periods (Hatanaka et al. 1985;Murata 1989). Fishing areas that developed only inautumn were identified in Classes 1, 3 and 7, beingrecorded from the central to northern areas of the Seaof Japan. In winter, fishing areas formed in moresoutherly areas, such as the southern areas of the YamatoRise and coastal areas of Hokkaido. Bearing inmind the spawning season and migration patterns ofT. pacificus during autumn and winter, it is reasonableto consider T. pacificus in these classes as mixedspawningrecruits.Fish migrations can be linked to periodic occurrencesand to events such as spawning and feedingmigrations (Laevastu & Larkins 1981). Although thecontrol of Todarodes pacificus migration is not wellunderstood, its northward migration to the northernSea of Japan and its southward autumn-winter migrationare thought to be for feeding and to search for suitablespawning grounds (Hanlon & Messenger 1996).Currents play a dominant role in determining the patternof migration (Healey 2000). There is a possibilitythat T. pacificus would have to utilize such flows tomigrate northward, in order to save energy for foragingin the northern Sea of Japan. Thus, the oceanographicfeatures of the TWC probably influence thespatial-temporal distribution of T. pacificus. Class 4,identified in May, June, and December along theJapanese coast from the Oki Islands to northern watersoff Honshu, coincides with the evolution of warmeddies influenced by interactions with the coastal currentalong the Japanese coast (Isoda 1996). Theseareas also correspond to the location of the TWC. Class6 developed from October to December (Fig. 10) andshowed the largest distribution of all classes. However,Class 6 corresponded to relatively deep-water areaswith depths greater than 500 m. Class 6 may be anarea through which squid merely pass on their way tothe spawning grounds in the Tsushima Strait or alongthe eastern coast of Korea (whichcorrespond to Class 5). It is of notethat some fishing areas occurred atsimilar times but at great distancesapart. For instance, Classes 1 and 3(Figs. 9 & 10) ranged from thenorthern waters of the east coast ofKorea to the west of Tsugaru Straitand the Yamato Rise and occurredin August and September. Thisindicates that squid in these regionscould be at a similar phase of thelife cycle, since portions of theautumn or winter spawning groupsfollow the TWC branches that flowoff eastern Korea and the Japanesecoast.
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