2026-02-18 福井県立大学,水産研究・教育機構,東北大学,京都大学舞鶴水産実験所
福井県立大学、水産研究・教育機構、東北大学、京都大学舞鶴水産実験所の研究グループは、カツオ(Katsuwonus pelamis)の眼球水晶体に蓄積する炭素・窒素の安定同位体比を分析し、孵化から漁獲までの回遊履歴を推定する新手法を開発した。従来の電子標識によるバイオロギングは高コストかつ追跡期間に制限があったが、本手法は生涯履歴の復元が可能。中西部太平洋で漁獲した33個体を解析した結果、熱帯域に滞留する個体と日本近海へ北上する個体が存在し、部分回遊が示唆された。資源変動の解明や持続的管理への応用が期待される。
図 1. カツオの水晶体を顕微鏡下で切片にする様子(A)、水晶体(B)と切片にした後の水晶体の中心部(C)。中心部には、孵化時期の同位体比が記録されている。
<関連情報>
- https://www.fra.go.jp/home/kenkyushokai/press/pr2025/20260218_press-katsuo.html
- https://www.fra.go.jp/home/kenkyushokai/press/pr2025/files/press0218katsuo.pdf
- https://besjournals.onlinelibrary.wiley.com/doi/10.1111/2041-210x.70201
眼水晶体の等角測量による外洋魚類回遊の微細構造復元 Fine-scale reconstruction of pelagic fish migration by iso-logging of eye lens
Jun Matsubayashi, Yutaka Osada, Katsuya Kimura, Yoshinori Aoki, Makoto Okazaki, Tetsuro Senda, Yuya Ueda, Naoto Matsubara, Yuichi Tsuda
Methods in Ecology and Evolution Published: 18 November 2025
DOI:https://doi.org/10.1111/2041-210x.70201
Abstract
- Understanding lifetime space use by pelagic animals is pivotal for ecology and fisheries management, but electronic tags are costly, labour-intensive and rarely able to capture juvenile movement. We implemented an iso-logging workflow that converts stable isotope chronologies in eye lenses into continuous migration tracks, and demonstrate its application to skipjack tuna (Katsuwonus pelamis).
- The δ13C and δ15N of muscle from 1122 skipjack were combined with oceanographic predictors in a geostatistical model to produce isoscapes of the western Pacific. Then, a newly developed dry-and-scrape protocol was applied to eye lenses from 33 adult skipjack and yielded high-resolution δ13C and δ15N time series. These isotope ratios were normalised to muscle–lens offsets and ontogenetic enrichment, and a Bayesian state-space model was used to estimate lifetime migration tracks for each individual.
- Ensemble reconstructions exposed two migration habits: most fish caught in the western tropical Pacific were lifelong residents, whereas several North Pacific fish had migrated there from tropical nurseries. This provides the first direct evidence of partial migration in a highly migratory pelagic fish.
- We show that the reconstruction of migration by iso-logging is a powerful approach for reconstructing the lifetime migration history of pelagic fish. This approach could be applied to a variety of other marine organisms, possibly providing a breakthrough for behavioural ecology studies of marine ecosystems.
