The Features of Demersal Fish Seasonal Distribution on the Pacific Shelf off the Northern Kuril Islands

Abstract—

The pattern of seasonal cycles of changes in the intra-annual distribution of fish in Pacific waters off the northern Kuril Islands is considered and their probable causes are determined. The subarctic structure of water masses along the Pacific coast off the northern Kuril Islands largely determines the conservatism of the vertical (bathymetric) structure of seasonal fish aggregations. The dynamic character of currents in the area off the islands with a large number of straits leads to significant variability in the location of fish aggregations in the direction along the coastline in interannual and seasonal aspects. In the autumn-winter period of the year, with cooling, the core of the total ichthyomass moves towards the upper slope of southeastern Kamchatka and the southern protrusion of the slope off Paramushir Island. In the spring-summer period, with warming, fish migrate dynamically along the slope to the south reaching lower depths in the shelf zone. At this time, fish are distributed along the entire Pacific coast off the northern Kuril Islands, forming separate aggregations on the shelf and upper parts of the slope off Paramushir and Onekotan islands, as well as on the slopes of the Fourth Kuril Strait and guyots near the above islands. The bathymetric range of fish habitat generally varies from 100–450 m in the cold season to 50–250 m in the warm feeding season.