Hokkaido Fish Hatchery, Eniwa, Hokkaido 061-1433, Japan
The relationship between marine survival and specific growth rate, and smolt size at release of masu salmon Oncorhynchus masou was examined by the method of individual tagging. A total of 4829 smolts of hatchery reared masu salmon were released on 28 May, 1998 in the coastal waters of southern Hokkaido Island, Japan. Seventy nine individuals were recaptured from June 1998 to May 1999 by coastal commercial fisheries in the coastal waters of Hokkaido and northern Honshu Island. A positive correlation between smolt size and recapture rate was observed. The mean smolt size of recaptured fish from June to July in 1998 was larger than that of all released individuals. The result suggested that the survival rate at the beginning of marine life was influenced by smolt size. A negative correlation between specific growth rate in the sea and smolt size was found. We conclude that an increase in smolt size is effective in increasing the recapture rate. However, the method is not effective in increasing the recaptured body size.