Since 1969 the fishing conditions of Alaska pollack, Theragra chalcogramma (PALLAS), had begun to show symptoms of decrease in the catch, a situation that had not appeared by that time on the trawling grounds in the eastern Bering Sea.
In order to find the clue to the above cause, the author carried out research on the length composition, catch per unit of fishing effort of Alaska Pollack and the oceanographic conditions of the sea bottom and the findings are as presented in this paper.
The results obtained are summarized as follows:
1. The length composition of Alaska pollack showed increased percentage of fish larger than 40cm in fork length due to the selective catching of larger sized fish from 1963 to 1966, a time when the catches were meager. Since then the percentage of fish larger than 40cm decreased year by year from 1967 to 1970 when total catches were actually greater.
2. The C. P. U. E. of Alaska pollack increased year by year from 1963 to 1968 with the rise in the unit of fishing effort, but began to slacken in 1969 and then decrease in 1970 in spite of the rise in the unit of fishing effort.
3. The water temperature was rated high in 1969, and low in 1970. But the C. P. U. E. of Alaska pollack in 1970 was less than that in 1969.
4. Estimating the results from length composition, the C. P. U. E. and the oceanographic conditions, the stock of Alaska pollack may have begun to symptoms of decrease in 1970.