Migration is vital for the continuation of a species. In this study, we explored migration hotspots of the vulnerable Hasu fish in Lake Biwa tributaries using two complementary methods: environmental DNA (eDNA) and visual counts. The study encompassed the known range of Hasu around Lake Biwa tributaries during its reproductive season. Monthly water sampling and visual inspection was conducted, from May to September, in 32 Class A tributaries—at the river mouth and within the river channel. Hasu eDNA was extracted from water samples and quantified using real-time polymerase chain reaction. Environmental factors were also assessed on-site, and their effects on eDNA and visual count trends evaluated using linear models and Akaike information criterion. eDNA was detected at sites where the fish were both observed and not observed. A zero-hurdle model revealed positive correlation between eDNA copies and visual counts of migrating Hasu, with pH having a reducing effect on the relationship (p < 0.05). Analysis of Hasu eDNA copies and visual count trends, with environmental factors as explanatory variables, indicates that Hasu is likely to be found in rivers that are wide and deep enough to accommodate migrating individuals, have fast-flowing currents, and sandy-gravel substrates during reproductive migration. Such rivers are mostly located on the western side of the northern basin and include the Ado, Chinai, and Shiotsuo Rivers. These could be considered as Hasu migration hotspots and require protecting if the population of Hasu in Lake Biwa is to be recovered.

中文翻译：

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利用环境 DNA 和视觉计数识别琵琶湖支流中的随性鱼类 Op​​sariichthys uncirostris 在繁殖季节的迁徙热点

迁徙对于一个物种的延续至关重要。在这项研究中，我们利用环境 DNA (eDNA) 和目视计数两种互补方法探索了琵琶湖支流中易受伤害的哈须鱼的迁徙热点。这项研究涵盖了哈苏繁殖季节期间琵琶湖支流周围的已知范围。5月至9月，每月对河口和河道内的32条甲级支流进行水质采样和目视检查。Hasu eDNA 从水样中提取，并使用实时聚合酶链式反应进行定量。还现场评估了环境因素，并使用线性模型和 Akaike 信息标准评估了它们对 eDNA 和视觉计数趋势的影响。在观察到鱼和未观察到鱼的地点都检测到了 eDNA。零障碍模型揭示了 eDNA 拷贝数与迁移哈苏视觉计数之间的正相关性，pH 对这种关系有减弱作用 ( p  < 0.05)。对哈苏 eDNA 拷贝数和视觉计数趋势的分析，以环境因素作为解释变量，表明哈苏很可能出现在足够宽、深足以容纳迁徙个体、水流湍急和沙砾基质的河流中。生殖迁徙。这些河流大多位于北部盆地的西侧，包括阿户河、奇内河和盐尾河。这些可以被视为哈苏族迁徙热点，如果要恢复琵琶湖哈苏族的数量，就需要对其进行保护。