Occurrence of ayu Plecoglossus altivelis altivelis larvae in the Hidaka estuary [Japan]
2006
Yoshimoto, Y.(Wakayama-ken. Fisheries Experiment Station, Kushimoto (Japan)) | Fujii, H. | Nakanishi, H.
The fluctuation of the number of ayu Plecoglossus altivelis altivelis larvae was investigated from 1992-1997 in different environmental condition at an observational station, 4 km upstream from the mouth of the Hidaka River and the river estuary. The number of downswept ayu larvae was estimated as 2-24x10E8 per year. Larvae appeared from October-March, with a peak from November-December, in the center of the flow at the river mouth. The larvae in the central part of the flow were 6-8 mm long in standard length. After becoming approximately longer than 10 mm in standard length, they removed their habitat from the central part of the stream to the bank side as if to avoid being swept down by rapid stream. The number of collected ayu larvae and their standard length in the central part of the flow at the river mouth showed similar values in both of the ebb and flow tide. Time lag of the number of ayu larvae at the river mouth is about 10 days appeared later than the peak of downswept ayu larvae observed at the upstream station.
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