Food Availability for First-feeding Walleye Pollock (Theragr chalcogramma) Larvae during Winter in and Near Funka Bay, Hokkaido, Japan, as Inferred from Copepod Nauplii Abundance

To clarify the relationship between the food availability for polock larvae and the hydrographic conditions in Funka Bay,horizontal distributions of water temperature,salinity and Oithona naupli(main food for larval polock)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 naupli in January of each year were not diferent significantly.In January 2003,the density of female O.similis(main producer of Oithona naupli)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.