A Few Examples of the Many Approaches to Salmon Resource Creation in Japan

Abstract

The chum salmon Oncorhynchus keta (Walbaum) resource of Japan has been dramatically improved by artificial propagation, and this resource increased rapidly in the 1980s. However, an unexpected decrease was observed in 1992, 1999, 2000, and 2008. An accurate resource evaluation of each year's class group is necessary to determine the appropriate method of managing the salmon resource, and the adult return rate is one of the indices that can be used for this purpose. This rate is calculated as a ratio of the number of recurrences (i.e., the total adult returns to rivers and coastal seas) to the number of chum fry stocked, and it has fluctuated around a total mean value of about 3% in Hokkaido and Honshu Islands in recent years. However, the adult return rate also varies by region from 0.1% to about 10%. The return rate of the northern area tends to be higher than that of the southern area, and that of the Pacific Ocean side tends to be a higher measurement of the local resource because the number of salmon caught by set nets, etc., in the coastal sea area catches might not be an accurate measure of the area's resources. This report introduces an example of a research approach in Japan that attempts to achieve high-ranking stabilization of this accurate adult salmon return rate.