Catch fluctuations of Japanese eel Anguilla japonica in the Tone River and Lake Kasumigaura [Japan]
2006
Nihira, A.(Ibaraki-ken. Freshwater Fisheries Experimental Station, Tamatsukuri (Japan))
The biomass of natural eels in Japan decreased rapidly in these 30 years or more. The eel catch in 2000's became about 20% in 1960's. Especially eel's catch in the Tone River including Lake Kasumigaura exceeded 1,000 tons at the end of 1960's. It occupied 1/3 of the all catches in Japan. It decreased to about 60 tons in 2000's. River-mouth barrages were made in the Hitachi River in 1963 and Tone River in 1970 for the flood control and the water availability. The number of eel's catches in Lake Kasumigaura and the Tone River decreased after completing those barrages made in the mouth of the river. The decrease ratio of the eel's catch in the Naka River, Lake Hinuma and the Kuji River where the barrages was not constructed is fewer than that of the Tone River and Lake Kasumigaura. It was estimated that eel's catch increased to ten times the value of present if the elver was able to migrate into Lake Kasumigaura. The construction of the fish way at the Hitachi River barrages is an important policy for increasing the eel's catch in Lake Kasumigaura.
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