Using birds as juvenile fish samplers: a comprehensive study of the life history of juvenile Chum salmon.

2021 Fiscal Year Final Research Report

• Project/Area Number: 17K15308
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Aquatic bioproduction science
• Research Institution: Toyo University
• Principal Investigator: Ito Motohiro 東洋大学, 生命科学部, 准教授 (80612332)
• Project Period (FY): 2017-04-01 – 2022-03-31
• Keywords: サケ幼魚 / 魚食性海鳥 / サンプラー / ウトウ / 初期生活史 / 由来河川

Outline of Final Research Achievements

Capturing juvenile salmon (10-15 cm) migrating in the open ocean after their first year is difficult and has been a black box in the life history of salmon. In this study, we revealed a part of the detailed ecological information of juvenile salmon during the period of high depletion by using fish-eating seabirds as samplers of juvenile salmon.
Otoliths of juvenile salmon collected from seabirds revealed a significant number of thermal signatures that can determine the river of origin, and otolith rings were analyzed to determine the growth rate salmon just after their seaward migration. DNA analysis of salmon muscle samples revealed the source of salmon population, and GPS logger data from seabird identified the locations where the juvenile salmons were foraged; the location of juvenile salmon's distribution during migration. Furthermore, we estimated the amount of juvenile salmon consumed by seabirds, during salmon's first year migration around northern Japan after release.

Free Research Field

海洋生態学

Academic Significance and Societal Importance of the Research Achievements

サケOncorhynchus ketaは重要な漁業資源であるが、近年、資源量の減少と母川への回帰率の低下が報告される。しかしながら、その原因は未だによくわかっていない。その理由の一つに、降海した個体の内9割が減耗するとされる1年目の幼魚期の生態がほとんど分かっていないということが挙げられる。本研究が明らかにした、サケ幼魚の初期生活史に関する様々な情報は、今後のサケ研究や資源評価、保全に有用な情報を付加することが期待される。さらに、困難だったサケ幼魚の安価な捕獲方法を提示し、海鳥類の魚類幼魚のサンプラーとしての有用性を明らかにしたことで、今後の魚類の幼魚研究の進展に対して大きな可能性を示した。