known distribution. Hence, the region indicated by
Class 5 could be a fishing area for both autumn and
winter spawning groups. Abundance of T. pacificus is
determined by recruitment during the autumn and
winter spawning periods (Hatanaka et al. 1985;
Murata 1989). Fishing areas that developed only in
autumn were identified in Classes 1, 3 and 7, being
recorded from the central to northern areas of the Sea
of Japan. In winter, fishing areas formed in more
southerly areas, such as the southern areas of the Yamato
Rise and coastal areas of Hokkaido. Bearing in
mind the spawning season and migration patterns of
T. pacificus during autumn and winter, it is reasonable
to consider T. pacificus in these classes as mixedspawning
recruits.
Fish migrations can be linked to periodic occurrences
and to events such as spawning and feeding
migrations (Laevastu & Larkins 1981). Although the
control of Todarodes pacificus migration is not well
understood, its northward migration to the northern
Sea of Japan and its southward autumn-winter migration
are thought to be for feeding and to search for suitable
spawning grounds (Hanlon & Messenger 1996).
Currents play a dominant role in determining the pattern
of migration (Healey 2000). There is a possibility
that T. pacificus would have to utilize such flows to
migrate northward, in order to save energy for foraging
in the northern Sea of Japan. Thus, the oceanographic
features of the TWC probably influence the
spatial-temporal distribution of T. pacificus. Class 4,
identified in May, June, and December along the
Japanese coast from the Oki Islands to northern waters
off Honshu, coincides with the evolution of warm
eddies influenced by interactions with the coastal current
along the Japanese coast (Isoda 1996). These
areas also correspond to the location of the TWC. Class
6 developed from October to December (Fig. 10) and
showed the largest distribution of all classes. However,
Class 6 corresponded to relatively deep-water areas
with depths greater than 500 m. Class 6 may be an
area through which squid merely pass on their way to
the spawning grounds in the Tsushima Strait or along
the eastern coast of Korea (which
correspond to Class 5). It is of note
that some fishing areas occurred at
similar times but at great distances
apart. For instance, Classes 1 and 3
(Figs. 9 & 10) ranged from the
northern waters of the east coast of
Korea to the west of Tsugaru Strait
and the Yamato Rise and occurred
in August and September. This
indicates that squid in these regions
could be at a similar phase of the
life cycle, since portions of the
autumn or winter spawning groups
follow the TWC branches that flow
off eastern Korea and the Japanese
coast.