2023 Fiscal Year Final Research Report

Aggregation pattern of large salmonids to the release site of chum salmon fry

Research Project

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Project/Area Number	19K06197
Research Category	Grant-in-Aid for Scientific Research (C)
Allocation Type	Multi-year Fund
Section	一般
Review Section	Basic Section 40030:Aquatic bioproduction science-related
Research Institution	Fisheries Research and Education Agency
Principal Investigator	Honda Kentaro 国立研究開発法人水産研究・教育機構, 水産資源研究所(札幌), 主任研究員 (00720707)
Co-Investigator(Kenkyū-buntansha)	長谷川功国立研究開発法人水産研究・教育機構, 水産資源研究所(札幌), 主任研究員 (00603325)
Project Period (FY)	2019-04-01 – 2024-03-31
Keywords	サケ稚魚 / ふ化放流 / 外来サケ科 / 捕食・被食関係 / 採餌効率
Outline of Final Research Achievements	Many people involved in the hatchery program in the Chitose River, Hokkaido have believed over the years that piscivorous large brown trout would aggregate at the release site of chum salmon fry from the surrounding area. In this study, we used acoustic telemetry, underwater visual censuses, and diet analysis to investigate the validity of this belief. None of the 34 brown trout tracked appeared vicinity of the release site during the fry release period, and visual censuses showed no increase in the number near the release site. Since brown trout c. 10 km downstream also preyed on a large number of fry released just before, it was suggested that there is no need for brown trout to go all the way upstream to the vicinity of release site to prey on fry drifting downstream within a short period after release. It was also found that brown trout restored their lowered nutritional status during the winter by feeding on chum salmon fry.
Free Research Field	魚類生態学
Academic Significance and Societal Importance of the Research Achievements	サケは近年来遊数が低迷しており、回帰率向上のための対策が急がれる。サケが大回遊する生活史を考慮すると、人為的に減耗を抑制できる範囲はごく限られる。ふ化場関係者は捕食性魚類が稚魚の放流地点に集まることで、多数の稚魚が減耗することを危惧してきた。捕食者の蝟集が事実で著しい場合、稚魚の放流地点を分散させるなどの対策によって総被食量を減らすことができるかもしれない。本研究では蝟集の真偽を確かめ、少なくとも約10kmの対象流程では捕食性の大型サケ科は稚魚の放流地点に集まらないことが明らかになった。よって、同様の流程では放流地点を分散させても総被食量は大きく変わらないことが示された。