Salmon in the North Pacific Ocean are widely distributed and migrate from the open sea to the coast in a broad area. When they have been captured by the drift gill-net, it has been bserved that they are gathered densely here and there in the net. But, the characteristics of their spatial distribution have not been clarified yet in this area. Judging from these phenomena, it is considered that salmon must have the gathering instict and make social grouping in these areas. The authors applied the method in which the number of captured fish for the net was taken as the stochastic process for analysis of these phenomena and tried to clarify the spatial distribution of the salmon in the above mentioned area. The number of fish include the four species; that is, pink, chum, red and silver salmon. Put the captured number of fish in the net as variables X(i) against numerical order of the net T, these variables fluctuate for their mean value as an irregular phenomenon. The auto-correlation coefficients and power spectra for the variables are calculated with regard to the fluctuations in the stochastic process. According to these calculations, it was deduced that the existences of remarkable power in the spectra would mean the grouping of the salmon. Using the data of 1960 and 1963 from the Okhotsk Sea, 1961 and 1963 from the Pacific Ocean, the calculations were performed by the equations (1), (2), (3) and (4). According to the results of these calculations, the various periodic components in the power spectra indicate the characteristics spatial distribution of the school.

No abstract

Though many biological studies have been made on the commercial-sized herring, Clupea harengus pallasi, in the northern part of the Okhotsk Sea in summer, knowledge on the distribution and biological characteristics of the juvenile in the same period is inadequate even today. The authors studied informations obtained from the measurements of about 2400 samples. The samples were obtained by surface gill nets, varying in mesh size from 30mm to 82mm, used for capturing juvenile salmon, and the samplings were conducted on the research vessel "Oyashio Maru" in the northern part of the Okhotsk Sea from August 17 to September 3, 1971. The results obtained are summarized as follows: 1) The shoals, composed of middle and large-sized fish (20-33cm) were found in the area off the Koni Peninsula, the small-sized fish (12-15cm) in the area off the Okhotsk, and the medium-sized fish (18-26cm) in the area off the Ayan. The area, where each shoal appears, seems to vary yearly. 2) The fish of 2-3 age were observed in comparative warm waters (13-14℃) in 1971, 12-13℃ in 1970 (Unpublished data). 3) Samples of the 4 age, caught in the area off the Ayan, were smaller in their average fork length, and heavier in the ratio of body weight to fork length, and higher in the mean maturity index {gonad weight×10^2/(body weight-gonad weight)} than those from the area off the Koni Peninsula. There is a possibility that the fish in the area off the Ayan may not belong to the Okhotsk population.1) 1971年8-9月にオホーツク海北部で行なわれたさけ・ます幼魚採集用の流網に混獲されたニシンを標本とし，各水域毎の魚群の組成ならびに4才魚の生物学的特徴について検討した。2) コニー半島沖は中-大型魚，オホーツク沖は小型魚，アヤン沖では中型魚がそれぞれ主体をなしている。集群水域は年により変動するが，一般的傾向としては水域による魚群組成の相違が現われる。3) 2-3才の若令魚は12-14℃の高温な水帯を中心として分布する。4) アヤン沖の4才魚はコニー半島沖のものに比べて体長は小さいが，肥満度ならびに成熟度指数が高い。アヤン沖ではオホーツク群以外の系群が含まれている可能性がある

No abstract

ON THE CORRELATION BETWEEN THE MIGRATION OF SALMON AND OCEANOGRAPHICAL CONDITION OF THE OKHOTSK SEA* Seikichi MISHIMA, Tatsuaki MAEDA and Motokazu UENO** Previously, authors reported on the constitution of salmon fishing grounds, the distinctive condition of sea water, and the result of fishing experiments in the Okhotsk Sea, and sug gested four sea areas as available fishing grounds. In the present paper they examined the correlation between the migration of salmon and the characteristics of sea wafer from the data made available by the "Hokusei Maru" of the Faculty of Fisheries Hokkaido University and the "Kumamoto Maru" , "Ariiso Maru", the research vessel of the Government, from June to August, 1963.