天竜川における副流路の湧水環境創出によるアユ産卵床の造成に関する研究

Abstract

Spawning redds of Ayufish (Plecoglossus altivelis) have been degraded by decrease in sediment supply and increase in turbidity derived from reservoir sedimentation in the lower reaches of the Tenryu River, Japan. We conducted a series of habitat surveys in the two reaches of the Tenryu River to seek the spawning redds and suitable physical conditions. Then, we found the spawning redds of the fish in the upwelling-zones of hyporheic water in the secondary channels. Based on the results of habitat survey, we conducted an experiment in the Tenryu River in order to create a new riffle connected with upwelling-zone of hyporheic water. The work resulted in successful creation of upwelling zone and we found the spawning redds of Ayufish in the new riffle, whereas no spawning redds were found in riffles in the main channel.