Distribution of ayu, Plecoglossus altivelis larvae in surf zones in the central area of Wakayama Prefecture, Japan

摘要

The abundance, size, and age of ayu Plecoglossus altivelis larvae were investigated to clarify the distribution pattern, using samples collected from 15 sites in surf zones in the central area of Wakayama Prefecture. The hatching date of ayu rangedfrom early October to early January, and was mainly between October and December with a peak in November. The fish hatched from October to 'November were widely distributed in the survey area as far as 15-20 km from the mouth of the principal rivers, whereas those hatched in December stayed near the river mouth. The relationship between the distribution pattern of ayu and the daily precipitation during the downstream migration showed that the distance of transportation of ayu larvae from the river mouthis longer in the specimens hatched in October-November (wet months) than in those hatched in December (dry month) . These facts suggest that the transportation of ayu would be affected by the river discharge at the time of the downstream migration of the newly hatched larvae to the sea.