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<p>The upstream migration and early post-settlement period of anguillid eels are important phases in the transition from a pelagic to a benthic lifestyle. However, little is known about the spatio-temporal changes in abundance, pigmentation stages, feeding habits, and other fundamental aspects during the early settlement period of Japanese eels. Field surveys were conducted in Hamana Lake and its small inflowing tributary where available freshwater habitats for eels were generally concentrated within ~1&#xa0;km from the estuary due to constraints imposed by weirs. Glass eels began arriving at the tributary estuary mainly in February and remained in low water temperatures during February and March (monthly mean: 10.2–12.1&#xa0;°C). Upstream migration into freshwater started in April, when the monthly mean water temperature increased to 14.4–20.9&#xa0;°C from April to May. Young-of-the-year (YOY) eels exhibited more advanced pigmentation stages at the freshwater station than at estuarine stations during the same periods. Feeding commenced earlier in freshwater, and the condition factors of the YOY were higher there than at estuarine stations until May. Catch per unit effort (CPUE) of the YOY eels decreased sharply after peaking in early spring. YOY eels did not appear at the uppermost survey site (~600&#xa0;m from the tidal limit) where larger eels predominated. These results suggest that growth and feeding conditions of YOY eels that arrived early in freshwater areas were favorable. However, the presence of weirs may lead to reduced availability of suitable freshwater habitats, the concentration of larger eels, and ultimately habitat deprivation for YOY eels, which could potentially weaken recruitment success.</p>

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Spatial and temporal dynamics of biological characteristics of recruitment-stage Japanese eels to the lower reaches of an obstructed Hamana Lake tributary stream

  • 期刊论文

  • 发表日期：

    2025年11月3日

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  • Nobuto Fukuda,
  • Kazuki Yokouchi,
  • Michael J. Miller,
  • Katsumi Tsukamoto

摘要

The upstream migration and early post-settlement period of anguillid eels are important phases in the transition from a pelagic to a benthic lifestyle. However, little is known about the spatio-temporal changes in abundance, pigmentation stages, feeding habits, and other fundamental aspects during the early settlement period of Japanese eels. Field surveys were conducted in Hamana Lake and its small inflowing tributary where available freshwater habitats for eels were generally concentrated within ~1 km from the estuary due to constraints imposed by weirs. Glass eels began arriving at the tributary estuary mainly in February and remained in low water temperatures during February and March (monthly mean: 10.2–12.1 °C). Upstream migration into freshwater started in April, when the monthly mean water temperature increased to 14.4–20.9 °C from April to May. Young-of-the-year (YOY) eels exhibited more advanced pigmentation stages at the freshwater station than at estuarine stations during the same periods. Feeding commenced earlier in freshwater, and the condition factors of the YOY were higher there than at estuarine stations until May. Catch per unit effort (CPUE) of the YOY eels decreased sharply after peaking in early spring. YOY eels did not appear at the uppermost survey site (~600 m from the tidal limit) where larger eels predominated. These results suggest that growth and feeding conditions of YOY eels that arrived early in freshwater areas were favorable. However, the presence of weirs may lead to reduced availability of suitable freshwater habitats, the concentration of larger eels, and ultimately habitat deprivation for YOY eels, which could potentially weaken recruitment success.