2009 Volume 73 Issue 1 Pages 1-7
Effects of oceanographic conditions and maturity on schooling and migration of common mackerel, Scomber japonicus, were analyzed based on fishing log of dip net fishing, oceanographic conditions, tagging experiments and maturation process around the fishing ground in Izu Islands. Spawning schools of the mackerel were caught at the shoal less than 200m of water depth where was covered with warm water from Kurosio. Sea surface temperature (SST) of the fishing ground was approximately 16℃ in the sexually maturing period of the mackerel until mid-February, and ranged I8-20℃ during spawning period until mid-June, indicating SST suitable for schooling coincides that for spawning. When the preparation of spawning was complete, the mature mackerel moved southward toward warm shoals where SST was optimum for spawning conditions by the influence of shifts of Kuroshio axis. Due to the rise of the temperature by the influence of warm water, the mackerel moved northward for cooler SST. Intrusion of warm water over 22℃ induced the mackerel to cease spawning and migrate northward for feeding in the late fishing season in mid-June. Thus, the intrusion of warm water from Kuroshio is deeply involved in schooling, spawning and feeding migration of the mackerel around the fishing ground in Izu Islands.
