アマゴの稚魚放流における分散放流の効果

摘要

We evaluated scatter stocking(releasing fish evenly)and point stocking(releasing fish at one location)of amago salmon Oncorhynchus masou ishikawae, in the research sections of a natural river.There were no significant differences in the survival rates between scatter stocking and point stocking.However four months after the initial stocking the survival rates of the scatter stocking groups were higher.It was also found that the growth of the fish in the scatter stocking groups was significantly better.Therefore, scatter stocking seems to be effective for short-term periods.However the survival rate of the wild fish was higher than that of both the scatter and pointing stocking groups.These results suggest that we should work to conserve the wild fish as well as the stocked fish populations.These efforts will help to improve the overall conditions of our rivers and streams for future generations of fish.