2003 Volume 67 Issue 2 Pages 78-87
Horizontal distribution and diel vertical migration of Euphausia pacifica were surveyed in the Tohoku waters, western North Pacific in the middle of April, 1998. The larval and immature stages of E. pacifica were few or not present in the cold waters strongly affected by Oyashio. The depth of distribution during the day tended to increase with the developmental stage from the calyptopis to adult stage in the offshore areas. The calyptopis stage, however, took diel vertical migration in the mid-deeper layer in the coastal areas, where adult E. pacifica were abundant in the upper layer during the night. The daytime distribution of adults was observed at a shallow layer compared with that of previous reports in the same area during the summer period. In the case of low concentration of chlorophyll α, E. pacifica was distributed in the deeper layers during the daytime. The diel vertical migration patterns in spring were explained to prevent cannibalism and predation.
