Habitat shift of ayu Plecoglossus altivelis altivelis in early stages from
waters adjacent to the bank to the center of flow in the Shimanto Estuary |
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Authors: | Isao TAKAHASHI Kensaku AZUMA Shinji FUJITA AND Izumi KINOSHITA |
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Institution: | Nishinihon Institute of Technology, Kochi, Kochi 780-0812;, Nishinihon Institute of Technology, Nakamura Office, Nakamura, Kochi 787-0019 and; Usa Marine Biological Institute, Kochi University, Tosa, Kochi 781-1164, Japan |
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Abstract: | ABSTRACT: To clarify the habitats of the ayu in the early stages of development in the Shimanto Estuary, the size and hatching date of the larval and juvenile ayu were examined. Sizes of larvae and juveniles were larger in the center of the flow area than in the waters adjacent to the estuary's banks, which suggests that larvae shift habitat to the center of flow from the waters along the estuary's banks. This shift began at approximately 20 mm body length. However, the resident term in the waters adjacent to the estuary's banks changed with the hatching dates; that is, the early and late-hatched larvae became short and long-term residents, respectively. A similar phenomenon was found also in the juveniles collected in the freshwater section that were migrating upstream. The growth rates of larval ayu in the waters adjacent to the banks tended to decrease with hatching dates. The fluctuations in growth rate with hatching date appear to be a factor leading to the variation of resident term. |
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Keywords: | ayu early stage growth rate habitat shift hatching date Shimanto River |
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