A few weeks ago the Asahi News on-line reported the following:
Sweet-fish: rivers all over the country were waiting for its fishing season. In recent years among anglers and fishermen there were opinions that "it is becoming smaller". It was the one-year fish which laid eggs in autumn. It seemed that the breeding season was delayed due to an increase in river water temperature caused by the warm climate. Among the going up-stream sweet-fish, the number of those unable to grow up in the sea was increasing.
In the investigation by the prefecture’s Regional Fisheries Research Laboratories in Shogawa in Toyama Prefecture which welcome the lifting of the ban on sweet-fish angling in June, it was found that while the length of the sweet-fish was 15-18 cm in the 1990s, in 2000s it was shorter by 2-3 cm. Mr. Shirataki Jiro (56) of Gifu Gujo, a sweet-fish angling expert who had visited the whole country such as Nakagawa (Tochigi Prefecture), Jintsu River (Toyama Prefecture), and Shimanto River (Kochi Prefecture) also said "there is a feeling that the sweet-fish going upstream from the sea is becoming smaller than before".
The same voice was also heard from anglers all over the country. A group meeting of the national lake and river aquaculture study group formed by the fishery research institutions from 25 cities and prefectures had come together to investigate the cycle for the fish going up-stream and down to the sea: the "drop". It issued an interim report in March this year: regarding whether the yearly timing for the up-stream in the river was advanced or delayed, it was seen that all over the country a tendency in delayed descending every year had started since around the 90s. In Nagara-gawa (
in 95 – 96 the peak of descending was mid-October to mid-November, last year it
was one month later than that period. Gifu
May be the life-cycle of the sweet-fish has been affected by the global warming.