US : Alaska salmon shrinks in body size – impact of climate change and feeding competition

 Recently CNN.co.jp reported the following:

米アラスカ州産のさけが小型化、気候変動や餌の争奪戦が影響

2020.08.23 Sun posted at 16:52 JST

（ＣＮＮ） 米アラスカ州産のサケが気候変動と数が増えているサケの間の競争激化などが原因で体が小さくなり続けているとの新たな研究報告書がこのほど公表された。

米カリフォルニア大学サンタクルーズ校の教授らの研究者たちがまとめたもので、サイズの縮小の主因はサケが太平洋で過ごす時間が少なくなっていることとも見ている。

研究者たちはアラスカ州魚類狩猟局が１９５７年から２０１８年まで収集したデータを分析。対象となったサケは１２５０万匹を超えたという。

この結果、川に戻ってくるサケの年齢は昔と比べ若返っていることを示す確固かつ一貫した傾向を突きとめた。海洋はサケの生息には危険な場所と化しつつあることをうかがわせているともした。気候変動が海洋の基礎生産力の変化につながっているとも説明した。

調査の対象となったサケは４種で、キングサーモンやギンザケなどが含まれる。これら４種についてはアラスカ州の住民が体が小さくなったことに気づいていたという。

今回の報告書作成の責任者である教授は、海洋でカラフトマスを中心にしたサケ類が増えたことがアラスカ州に戻ってくるサケの体が小ぶりになったこととも関係があると指摘。

太平洋北部での生息数の多さは記録的な水準にあり、アラスカ州やアジアでの孵化（ふか）活動が一因と分析。結果的にサケの間で餌の争奪戦が起きるとも説明した。

報告書作成に加わったアラスカ大学の専門家は、研究者たちが次に取り組むべき課題として望んでいるのは太平洋そのもので生じている変化の分析だと述べた。

Translation

(CNN) A newly published research report disclosed that the salmon from Alaska of the United States continued to shrink in body size because of climate change and an increase in the number of salmon intensified competition among them.

Based on what was gathered by researchers from the professors of the University of California, Santa Cruz, it seemed that the main reason for the size reduction of salmon was that they spent less time in the Pacific.

Researchers analyzed data collected by the Alaska Department of Fish and Hunting from 1957 to 2018. The number of targeted salmon exceeded 12.5 million.

As a result, they found a firm and consistent tendency to show that salmon returning to the river were younger than they were in the past. It also suggested that the ocean was becoming a dangerous place for salmon to inhabit. They also explained that climate change had led to changes in the basic productivity of the ocean.

Four types of salmon were surveyed, including King salmon and Coho salmon. Alaska residents were aware that the body of these four species had become smaller.

The professor who was responsible for preparing this report had pointed out that, in the ocean, an increase in Salmonidae, mainly the pink salmon was linked to the smaller body of salmon that returned to Alaska.

The high population in the northern Pacific Ocean was at a record level. In an analysis one reason for that was due to hatching activities in Alaska and Asia. As a result, it explained that there was a battle for feeding among the salmon.

Experts at the University of Alaska who took part in the report said the next challenge to researchers who wanted to tackle the matter was to analyze the changes that were taking place in the Pacific itself.

              So, any changes in the condition of an ocean could affect the living things in that area. Our living environment is changing quickly due to the global warming.