STUDIES ON FISHING CONDITIONS OF THE DOLPHIN, CORYPHAENA HIPPURUS, IN THE WESTERN REGIONS OF THE SEA OF JAPAN-XII:THE SIZE OF A DOLPHIN SCHOOL

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The size of a dolphins school accompanying a single "Tsukegi" was examined using the data of Shiirazuke fishery off Shimane Prefecture during the fishing season (June through October) in 1964. The catch data from 2, 447 operations were analysed and the following results were obtained; 1) The numbers of dolphins per single operation of the dolphin purse seine using "Tsukegi" ranged from one to 590 (Table 1). The range, however, varied from year to year. 2) As the fishing season went on, aged dolphins decreased in number and replaced by young fish and later in the season the latter be came the main constituent of the catch. At the same time, the number per single "Tsukegi" increased (Fig. 1 and Table 1). 3) The seasonal variation in the size of a dolphin school accompanying single "Tsukegi" may be caused by the ecological differences between the spawning schools (aged fish) and the feeding schools (young fish). 4) It is considered that a migrating school of dolphins is made up of one to 3 individuals for large sized fish, 4 to 10 for medium sized fish and several tens to several hundreds for small sized fish.
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