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<p>The diel vertical migrations (DVM) of Japanese eels were previously studied during their spawning migrations, but what determines their swimming depths is unknown. Ten silver-phase Japanese eels were released off the Japan east coast near the end of the Kuroshio Current with pop-up archival transmitting tags attached. Three tags transmitted the recorded data after the eels traveled various distances from the release location, ranging from nearby (Eel-H, 23.7&#xa0;km), farther northeastward (Eel-I, 331.8&#xa0;km), to far to the southeast (Eel-F, 1051.6&#xa0;km). Two of three individuals performed diel vertical migration during tracking, but the others showed indistinct daily rhythms in bottom layers. The DVM of Eel-F showed a similar pattern as previously published Japanese eel DVM behaviors. Eel-I experienced gradually decreasing water temperatures with the progress of the tracking, and it was estimated to have arrived in the colder environment of the Kuroshio-Oyashio confluence region at around 3 January 2011. Eel-I experienced colder temperatures and swam at shallower depths in daytime and nighttime. These results indicate that the DVM of Japanese eels is likely affected by not only light but also water temperature. This study led to a hypothesis that a combination of motivations for DVM based on light and thermal incentives determines the swimming depths of Japanese eels during their oceanic spawning migrations.</p>

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Cold environment influences on diel vertical migration of silver-phase Japanese eels in the Kuroshio-Oyashio confluence region

  • 期刊论文

  • 发表日期：

    2025年10月28日

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  • Takatoshi Higuchi,
  • Shun Watanabe,
  • Ryotaro Manabe,
  • Michael J. Miller,
  • Kim Aarestrup,
  • Jun Aoyama,
  • Eric Feunteun,
  • Katsumi Tsukamoto

摘要

The diel vertical migrations (DVM) of Japanese eels were previously studied during their spawning migrations, but what determines their swimming depths is unknown. Ten silver-phase Japanese eels were released off the Japan east coast near the end of the Kuroshio Current with pop-up archival transmitting tags attached. Three tags transmitted the recorded data after the eels traveled various distances from the release location, ranging from nearby (Eel-H, 23.7 km), farther northeastward (Eel-I, 331.8 km), to far to the southeast (Eel-F, 1051.6 km). Two of three individuals performed diel vertical migration during tracking, but the others showed indistinct daily rhythms in bottom layers. The DVM of Eel-F showed a similar pattern as previously published Japanese eel DVM behaviors. Eel-I experienced gradually decreasing water temperatures with the progress of the tracking, and it was estimated to have arrived in the colder environment of the Kuroshio-Oyashio confluence region at around 3 January 2011. Eel-I experienced colder temperatures and swam at shallower depths in daytime and nighttime. These results indicate that the DVM of Japanese eels is likely affected by not only light but also water temperature. This study led to a hypothesis that a combination of motivations for DVM based on light and thermal incentives determines the swimming depths of Japanese eels during their oceanic spawning migrations.