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reported a close association between swordfish longlineeffort and oceanic features, such as shelf breaksand thermal fronts. Herron et al. (1989) found that thebutterfish catch rate increased with an increase in SSTgradient. These studies show that frontal featuresstrongly influence the biological productivity of anarea in terms of the presence of secondary producers,which attract higher trophic levels feeders, such asTodarodes pacificus. Class 1 and Class 3 fishing areasformed at the center of the Sea of Japan, around theYamato Rise. Isoda (1994) pointed out that the polarfront stretches across latitude 40°N, and Classes 1 and3 formed to the north and south area of this front,respectively.Isoda & Saitoh (1993) analyzed satellite SST imagesand hydrographic data along the east coast of Korea.Their research showed warm eddies intruding northwardfrom spring to summer around the Ulleung Basin,and the presence of relatively stable northward currentsalong the eastern coast of Korea in autumn. Kimet al. (2002) reported the characteristics of the temporalvariations in sea level at Ulleung Island and concludedthat short-term variations in sea level arecaused primarily by the movement of the warm eddiesaround the Island. Choi et al. (1997) noted that thesquid-angling fishery started to move north in Apriland then south in September. Mesoscale eddies arealso important in the enhancement of phytoplanktonproduction (e.g. Saitoh et al. 1998) and the distributionof Pacific sardine larvae (Logerwell & Smith 2001). Inour results, Class 2 fishing areas were mainly distributedaround Ulleung Island from June to December. Ifhigher prey densities are associated with shelf-breakfronts and eddies, the consistent presence of fronts andeddies comprises predictable feeding locations forhigher trophic level feeders which take advantage ofincreased prey densities, and also a predictable fishingarea. The dynamics of warm-water eddies probablyalso affect squid fishing area formations, as suggestedby the fishing area distributions of Class 2 and thestudy of Choi et al. (1997).In the laboratory, Bower & Sakurai (1996) observedthat Todarodes pacificus females rest on the bottomjust before spawning. Similarly, bottom trawls oftencollect exhausted, spent females on the shelf and slopeat 100 to 500 m depth (Hamabe & Shimizu 1966), indicatingthat spawning females would concentrate atdepths between 100 and 500 m. Thus, topography mayaffect squid distribution. The main autumn and winterspawning grounds form around the Tsushima Strait(Murata 1989, and present Fig. 2). Kiyofuji et al. (1998)identified the inshore area of Korea’s east coast as apossible spawning ground, primarily using satelliteSST and topography data. Class 5 corresponds to this
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