Spawning redds distribution of Biwa salmon in ten inlet streams of Lake Biwa, central Japan in 2015

Abstract

We surveyed the distribution of Biwa salmon spawning redds in eleven inlet streams of Lake Biwa, from late October to early December 2015. We confirmed spawning redds in ten streams, with the exception of the Takashimakamo River, and analyzed their distribution in each streams. Spawning redds tend to be formed in the same section of stream every year, and are especially prevalent in lower sections of weir or dried up areas, which prevent upstream migration. However, when blockages or disturbances are cleared through stream discharge stabilization or the weir removal, mature fish spawn in the upper reaches of the stream. The results of this survey, along with information obtained from local resources, suggest that small inlet streams also serve as spawning site for Biwa salmon. Therefore, we propose that stream administrators avoid conducting river work projects during the peak of spawning season from October to May, when redds density within stream sections is the highest, due to large number of eggs or alevins that remain inside spawning redds during this time.