How have spawning ground investigations of the Japanese eel Anguilla japonica contributed to the stock enhancement?

Abstract

After Schmidt’s discovery of the spawning area of the Atlantic eels Anguilla anguilla and A. rostrata, the search for the Japanese eel A. japonica began in the Pacific Ocean. In 1991, the spawning area of the Japanese eel was determined to be the western North Pacific. Because of enthusiastic research, eggs and maturing eels have been collected in the Japanese eel. These findings are the first for one of the 19 freshwater eels. The population sizes of the Japanese and Atlantic eels are linearly decreasing. Thus, these eel population sizes are considered outside of safe biological limits, and the current fisheries are not sustainable. Artificial propagation has not yet succeeded for the freshwater eels. Stock assessment and management of the European eel have received increasing attention; however, such assessments and management of the Japanese eel have not yet been seriously considered. This paper is an overview of the results of intensive spawning ground investigations of the Japanese eel and describes how the outcomes of these studies have contributed not only to biological interests but also to stock enhancement. During the past 20 years of expeditions, noticeable findings have only been collected for wild eggs and mature adult specimens in spite of the expenditure of large research grants and the large amounts of time invested. The outcomes throughout an expedition do not necessarily contribute to the development and improvement of artificial breeding techniques and stock enhancement. Thus, eel research should be more focused on the studies related to eel stock management.