Distribution of walleye pollock Theragra chalcogramma along the coast of southeastern Hokkaido [Japan], in the early summer

This study describes the distribution characteristics of walleye pollock by depth and area, along the Pacific coast of southeastern Hokkaido, in the early summer. THe pollock were collected with midwater or bottom trawl net. Temperature at the depth in each tow was within the range from 1.4 to 3.4 degrees C. On the bottom, almost all the pollock appeared in 100 and 200m depth zone. The pollock of 1 to 3 years old were numerically dominant in the 100m depth zone, although those of 3 years old or more were mainly present in the 200m depth zone. Difference in age composition in respective survey area showed the aggregation of pollock in 100m zone of the Otsu area. In the midwater, most of the pollock were 2 or 3 years old. Most of the pollock in each collection in the midwater trawl survey consisted of 1 or 2 age groups that ranged from 2 to 5 years old. We discuss the probable effect of the biological and physical environment regarding the distribution of pollock