ACOUSTIC OBSERVATION OF SPAWNING WALLEYE POLLOCK THERAGRA-CHALCOGRAMMA AND HYDROGRAPHIC CONDITION IN FUNKA BAY

The distribution and behavior of so-called spawing walleye pollock The ragra chalcogramma around Funka Bay were investigated during the acous tic survey by the R/V ''Ushio Maru'' in late 1993. Three types of echo , namely, near surface echo patches, near bottom echo patches and the sound scattering layer (SSL) in the middle layer, were recorded on the echogram of the dual frequency quantitative echo sounder. Hydrographi c data by CTD observation showed that cold and less salty water mass b elow 5-degrees-C and 33.5 layers on the bottom of the shelf of Oshima Peninsula then formed a water front along the boundaries to surrounded the warmer and more salty waters. By comparing the hydrographic and a coustic dana, the sound scattering layer appeared along the water fron t and demersal echo patches were found in great numbers in the cold wa ter mass. Activity of fishing boats and hydrographic conditions in thi s area suggested that the demersal echo patches were the schools of wa lleye pollock which were migrating for spawning and the sound scatteri ng layer consisted of zooplankton aggregation in the water front. Dist ribution of the echograms indicated that the height of fish schools we re 1 to 4 meters and the SV of the echo were about -65 to -60 dB. The density of the schools of walleye pollock along the transects were 5.8 in November to 8.1 shoals/nautical mile in December, respectively.