Estimation of population number of ayu [Plecoglossus altivelis] in the Nezugaseki River [Japan]
2006
Uchida, K.(National Research Inst. of Fisheries Science, Ueda, Nagano (Japan). Freshwater Fisheries Lab.) | Shimizu, A. | Abe, S. | Sato, T. | Katsura, K. | Sakano, H.
In 2001-2003 population numbers of ayu were estimated by direct underwater counting with a line transect method from April to December in the Nezugaseki River. Ayu migrated upstream from the sea into the river on May to June in 2001-2003. The maximum numbers of ayu in the river were estimated as 70,000, 105,00 and 27,000 individuals, respectively, and the fish survived 11-18% on October and then spawned. In 2003 a mark-recapture test revealed that the hatchery-reared ayu released in the Nezugaseki River showed similar survival and growth to wild ayu stock.
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