因為天氣暖化香魚未能充分成長

A few weeks ago the Asahi News on-line reported the following:

アユ、温暖化で小型に？　産卵遅くなり海で成長しきれず

中山由美

2014年6月1日10時22分

　全国の河川で漁期を迎えているアユ。近年は釣り人や漁師から「小さくなった」との声が相次いでいる。秋に産卵する一年魚だが、温暖化による川の水温上昇で産卵期が遅れ、海で成長しきれないまま遡上（そじょう）するアユが増えているようだ。

　６月にアユ釣り解禁を迎える富山県の庄川で県水産研究所が調べたところ、アユの体長は１９９０年代に１５～１８センチあったのが、２０００年代はそれより２～３センチ小さかった。那珂川（栃木県）、神通川（富山県）、四万十川（高知県）など全国を訪れる岐阜県郡上市のアユ釣り名人・白滝治郎さん（５６）も「海から遡上するアユが、昔より小さくなった感じがする」と話す。

　同じような声は全国の釣り人からも聞かれ、２５都県の水産研究機関が集まる全国湖沼河川養殖研究会の部会は、遡上と海へ下る「降下」の時期を調べ、今年３月に中間報告を出した。遡上の時期は河川や年によって早まったり遅くなったりしていたが、降下は９０年ごろから全国的に年々遅れる傾向が見られた。長良川（岐阜県）では、降下のピークが９５～９６年は１０月中旬～１１月上旬だったが、昨年はそれより１カ月遅かった。

(試譯文)

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 (Gifu Prefecture), while in 95 – 96 the peak of descending was mid-October to mid-November, last year it was one month later than that period.

May be the life-cycle of the sweet-fish has been affected by the global warming.