猿谷ダム湖(奈良県)の水位変動が生物へおよぼす影響

抄録

The changes of water level in the Sarutani reservoir are caused by the amount of rainfall, water-drainage to the water power, irrigation and control of the flood. No aquatic plants and no limno-gastropoda are found in this lake, due directly or indirectly to the high frequency and great degrees of the annual change of the water level. The lake shores are so steep that it is difficult for the sediments and organisms to deposit or to stay on the bottom of the shore zone. Such a zone may be unfavourable to the habitats for almost all species of aquatic plants and limno-gastropoda. The standing-crops of Zacco platips and Zacco temminkii are ample in this lake ; this depends on the following two facts : 1) the spawning period of the fishes agrees with the period of comparatively slight change of water level in this lake, and 2) the egg period of the fishes is short. Hypomesus olidus is not so abundant in this lake, in spite of that the young fishes of this species have been stocked annually. It can be said that the natural increase of this fish is controlled by the next two reasons, i.e. 1) its spawning time falls in the period of low water level in winter in this lake, and 2) the egg period is long.