Swimming speed of sardine school on the basis of aerial survey.

Abstract

The flight surveys were conducted in the waters off the southeast coast of Hokkaido where a big catch of sardine Sardinops melanosticta has been taken during summer and autumn seasons. In order to examine the swimming speeds of schools, two kinds of survey, such as experiments and observations, were conducted near the fishing ground on Oct. 9 and Sept. 29, 1985 respectively. In the experiments five floaters were airdropped at a regular interval to intersect the target schools from the rear to the front. After that, relative changes between the school and the floaters were compared. On the other hand, the observations was carried out shuttling the same transect in order to observe the movements of a number of schools. From the results of the experiments the cruising speeds lie between 1.2-4.1BL/s (0.4-1.5kt). The result obtained by the observation was 4.3kt, which was larger compared with the data described above. The schools which were chosen as the subject in the experiments were elongate in shape and the longest dimensions of the schools ranged from 300-1, 500m. The results may suggest that the size of schools have an effect on the speed, as the speed of school decreases with an increase in size.