Seasonal and Annual Changes of Oceanographic Condition during Early Ocean Life of Chum Salmon in the Coastal Waters of Okhotsk Sea, Eastern Hokkaido

摘要

Two diffrent currents affect oceanographic conditions in southern part of the Okhotsk Sea along the Hokkaido coast. In winter the East Sakhalin Current characterized by low temperature and salinity flows along the Hokkaido coast with sea ice. In summer the Soya Warm Current (SWC) characterized by high temperature and salinity flows southeastward from Soya Strait along the coast. In spring, these current systems are replaced, so that the temperature, salinity and nutrients change extremely. These extreme changes in the oceanographic conditions may affect the early marine survival of juvenile chum salmon. We investigated to clarify the relationship between seasonal and annual fluctuations of oceanographic condition and early ocean life of chum salmon. Physicochemical and biological conditions were examined every 10 days from April to July in 2002-2005 at 12 stations in the coast of Abashiri Bay, eastern Hokkaido (Fig. 1). Water temperature and salinity profiles were measured by using memory STD at all stations. Water samples in each depth (0, 10, 20, 30 and 40 m) were collected with Van Dorn Bottles for nutrients and chlorophyll-a analyses at two stations off the mouth of the Abashiri River (Stations B1 and B3).