SEASONAL MIGRATIONS AND OCEANOGRAPHIC CONDITIONS FOR CONCENTRATION OF THE JAPANESE FLYING SQUID (TODARODES PACIFICUS STEENSTRUP, 1880) IN THE NORTHWESTERN JAPAN SEA

摘要

The distribution of the squid Todarodes pacificus in the north-western Japan Sea (38-45°N, 130―139°E) is analyzed in relation to the water masses and vertical water structure, using data from scientific and commercial catches of the squid and oceanographic data obtained by Russian and Japanese research vessels in 1986-1997. Seven zones of different types of water structure exist in the upper 200 m layer in the region: the Subtropical and Subtropical-transformed water types south of the Polar Front; the Interfron-tal and Interfrontal-transformed water types within the zone of the Polar Front; the Subarctic, Coastal, and Primorye Current types north of the Polar Front. The squid migrate into the Russian Exclusive Economic Zone (EZZ) of the Japan Sea in June. From July to October, the squid schools distribute widely over the whole Russian EEZ area, and concentrate usually in the Subtropical and Subtropical-transformed zones from June to September. In the Interfrontal zone, squid aggregations occur in June and September-October, in the Interfrontal-transformed zone (in June-October), in the Subarctic zone (in July and September-October), and in the Coastal zone (in July-October). The squid concentrations were located near the fronts (southern and northern divisions of the Polar Front offshore, or benthic front at the bottom of Primorye shelf). Concentrations of T. pacificus are formed under certain favorable environmental conditions: optimum water temperature, high gradient in the thermocline, and thin upper mixed layer. The highest concentrations of T. pacificus were formed in the zones with stable, steep, and shallow thermocline when the temperature was at its optimum for the squid.