ベーリング海東部における底曳綱漁場の研究III

Abstract

From the trawl fishing grounds in the eastern Bering Sea, the author collected the specimens of yellow-fin sole, Limanda aspera (PALLAS), which were caught by the training ship “Oshoro Maru” of the Faculty of Fisheries, Hokkaido University, during the 1st to 11th of July, 1963. The author studied the relation between the age and the size of yellow-fin sole by the otolith examination, and analysed the annual variation of the length frequency distribution. The results obtained are summarized as follows: 1. The growth of yellow-fin sole was very slow, and the number of females was remarkably more than that of the males. The average length of the females was larger than that of the males; and this difference increased over the 9 year old groups. 2. The average length of fish in the 4 and 5 year old groups in the eastern Bering Sea were somewhat larger than those in the Chukchi Sea, but generally smaller than those of fish shoals in the west coast of Kamchatka. 3. The age composition of the fish examined were from 4 to 14 year old groups, and the 8 year old group occupied 20.7% of all. Then came the 9, 6 and 5 year old groups in that order, and the percentage of the 7 year old group was very low. The 7 year old group was born in 1956 when the water temperature was rather low, whereas the 8 and 5 year old groups of high percentage were born in 1955 and 1958 when the water temperature were rather high. This quantitative fluctuation among the year class groups reasonably be due to the annual variation of the cold water mass in the year when they were born. 4. The author compared the length composition of yellow-fin sole caught in 1963 with that of 1956 when fishing intensity were not so high, and with 1959 and 1960 when the effect of high fishing intensity began to appear, and consequently recognized that the percentage of larger sized and higher aged fish was decreasing year by year.