放流時における人工種苗アユの分散-2-初期分散と再捕

概要

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This is a study of the movements of hatchery-reared juveniles of ayu, Plecoglossus altivelis, released in a river, to determine the effect of the release point on the distribution and the recapture of ayu. The distribution of 17, 000 hatchery-reared ayu released in the Tsubusa river, Oita Pref., Japan in 1975 was observed for 10 days after the release. The distribution of recapture, which occurred from June to October, was recorded. The distribution and relative density on the 10th day after the release were estimated by the density of feeding marks on the rocks. The downstream and upstream dispersal speeds were 0.8km/day and 0.3km/day respectively. Most of the released fish swam downstream and considerable numbers of them apparently left the study area and never returned to the area because of the dam. The majority of fish remaining in the stocking area was distributed downstream of the release point. The dispersion that occurred within 10 days seems to determine the distribution of ayu throughout the fishing season. The low recapture rate of hatchery-reared ayu seems to be due to the high loss of fish from the stocking area during this period. Consequently the recapture may be increased by releasing fish at the uppermost part of the stocking area.
日本水産學會の論文