Vertical Distribution of the Japanese Sardine in Relation to Temperature and Thermocline at the Purse Seine Fishing Grounds East of Japan

Abstract

The vertical distribution of sardine was compared with vertical temperature structujre in the fishing grounds between southeast of Hokkaido and est of Choshi from July ot December 1980. The water temperature at the layer, in which sardine lived, ranged widely from 5.6°C to 18.0°C and it varied with spatial and temporal changes of the fishing grounds. Verticvally, Sardine were distributed from the surface to the depth of about 115m. But the depth where they lived and the structure of their school varied with changes of the thermocline depth rather than with the temperature itself, In connection with this, it was found that the fish schools came to live in shallower layer when the seasonal thermocline became sharp and rose up to shallower layer. This resulted in the schols becomming thinner vertically but occupying a wider space horizontally.