抄録
This paper describes a method of estimating the fishing grounds of salmon according to characteristic types of echo image. We computed the swimming depths and speeds of reflecting bodies. The echo sounder used was the 28 KC ultrasound, a transducer having 28 degrees of effective beam angle. It was attached to the bottom of the ship.
The recording range of the echo sounder was 150m, the number of transmissions of ultrasound waves per minute was 450, and the pulse width was 1.5 millisecond. Time marks were recorded on paper.
These experiment were undertaken in gill-net fishing of salmon by the training ship “Hokusei Maru” of the Faculty of Fisheries, Hokkaido University, in the Okhotsk Sea in 1964 and 1966.
In this paper, the author compares the information about salmon obtained from the echo pattern with the actual catch of salmon.
The results obtained are summerized as follows;
1) The swimming speeds of reflecting bodies were computed according to the echo patterns on the basis of some assumptions.
2) The distribution of salmon estimated from the swimming depths and speeds of the reflecting bodies corresponded comparatively well with the salmon catch in the Okhotsk Sea.
3) Further improvement in the use of the echo sounder will enable us to detect the salmon distribution more accurately.
