サバ群の行動とその要因について-I

石狩湾におけるサバ群の去来状況について

抄録

Movement of the mackerels has been investigated on the basis of catch data provided by the purse seiners having operated on the Ishikari bay insummer seasons between 1951 and 1954. According to the investigation, it is found that the mackerels aggregate into several subschools. These subschools enter one after another into the fishing ground at an interval of about seven days, which corresponds to the duration between waxing and waning of the moon. Annual change is found in regard of arer and time, in which the earliest subschool for the year appeared. The subschool separates into two or more parts or join with the other, probably depending upon the environmental conditions. It is believed that the environments affect duration of time, for which each subgroup stays in the fishing ground.