Permalink : http://hdl.handle.net/2115/32484

KEYWORDS : Oithona similis;Oithona nauplii;Reproduction;Food conditions;First-feeding walleye pollock;Theragra chalcogramma;Larvae;Funka Bay;Hokkaido;Japan

To clarify the relationship between the food availability for pollock larvae and the hydrographic conditions in Funka Bay, horizontal distributions of water temperature, salinity and Oithona nauplii (main food for larval pollock) were investigated in winter from 2001 to 2003 in and near the bay. In January 2001 and 2003, the Oyashio coastal cold-water mass and the Tsugaru warm-water mass were co-distributed in the bay and its mouth region, but in January 2002, the Oyashio coastal cold-water mass has already exchanged with the Tsugaru warm-water mass. The median abundances of Oithona nauplii in January of each year were not different significantly. In January 2003, the density of female O. similis (main producer of Oithona nauplii) was higher in the Oyashio coastal cold-water mass than in the Tsugaru warm-water mass, while the densities of Oithona N1 in the Oyashio coastal cold-water mass and the Tsugaru marm-water mass were almost identical. These data indicate that the high activity of the individual reproduction is occurred in the Tsugaru warm water. From the results, it is considered that the warm-water temperature and the reproduction of O. similis in the Tsugaru warm-water mass in winter in Funka Bay support the larval feeding success.