中禅寺湖におけるサケ科魚類とくにヒメマスの鉛直分布について

概要

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Acoustic surveys were carried out to examine the diurnal-nocturnal behavior of Salmonidae mainly consisting of Hime salmon Oncorhynchus nerka in Chuzenji Lake located around 139°28' E, 37°45' N, with an area of 11.3 km2, a maximum water depth of 172m, and an altitude of 1, 271 m.In summer and autumn, a remarkable level of themocline was shown between depths of 10 and 30m, and the water temperature range was more than 15°C at the top of this and less than 5°C at the bottom. During the night many Salmonidae were dispersed in the surface layer (summer: 10-40m, autumn: 20-30m) of the whole lake area, and in the daytime ascend to a shallower layer (summer: 3-20m, autumn: 10-20m). But during the day, their number was very small compared with the night-time. The reason for this was estimated as horizontal maldistribuion. In winter, the water temperature was stabilized at 5.2 ?? 5.4°C in all layers, and Salmonidae were dispersed in the bottom layer (100-172m) around the deep area of the lake during the day, and were dispersed in the surface layer (20-60m) of the whole lake area at night.