Abstract

Mayfly larvae (Ephemeroptera), Diptera larvae, and adult water mites (Hydracarina) dominated in the winter syrton of a small salmon river. No significant linear dependence of the number of drifters entering the nets on the filtered water volume was found; therefore, we used not the syrton density (ind./m³), but the data of the actual catches. The vertical distribution of drifting invertebrates of different taxonomic affiliation had its own characteristics. The drift intensity of invertebrates increased in the daytime under conditions of good illumination of the water column. We assume that this fact is indirectly related to the low water temperature, which limits the swimming ability of drift-feeding fish, which, in turn, become more vulnerable to ichthyophagous endothermic predators. Altogether this preconditions fish’s predominantly sedentary, secretive lifestyle during daylight hours in winter. In December, most daytime drifters migrated close to the water surface and, in January, on the contrary, they kept near the bottom. The latter may be due to the overwhelming effect of lower daytime air temperatures, since the river channel was not completely covered with ice until mid-February. After a heavy February snowfall, the upper water layers of the river flow turned out to be isolated from the effect of air temperature, and the level of illumination of the water column during the daytime hours corresponded to the period of late twilight. As a result, the fish became less accessible to semiaquatic endothermic predators, the intensity of invertebrate drift in the daytime decreased sharply, and the vertical distribution of drifters along the stream became fairly uniform.

中文翻译：

---

小鲑鱼河漂流无脊椎动物垂直分布的冬季动态

摘要

蜉蝣幼虫（蜉蝣目）、双翅目幼虫和成虫水螨（水螅）在一条小鲑鱼河的冬季水螨中占主导地位。没有发现进入网的漂流数量与过滤水量存在显着的线性相关性；因此，我们没有使用 syrton 密度 (ind./m ³），而是实际捕获量的数据。不同分类归属的漂流无脊椎动物的垂直分布有其自身的特点。在水体光照良好的条件下，白天无脊椎动物的漂流强度增强。我们假设这一事实与低水温间接相关，低水温限制了漂流进食鱼的游泳能力，反过来，它们更容易受到鱼食性吸热捕食者的攻击。总而言之，这是鱼类在冬季白天主要以久坐、隐秘的生活方式为先决条件的。12月，大多数白天漂流者迁徙到靠近水面的地方，而1月则相反，它们停留在水底附近。后者可能是由于白天气温较低的压倒性影响，直到二月中旬，河道才完全被冰覆盖。二月的一场大雪过后，河水的上层水层不受气温的影响，白天水柱的光照水平与黄昏时期相对应。结果，鱼类变得越来越难以接近半水生吸热捕食者，白天无脊椎动物漂流的强度急剧下降，漂流沿溪流的垂直分布变得相当均匀。白天水柱的照明水平与黄昏时期相对应。结果，鱼类变得越来越难以接近半水生吸热捕食者，白天无脊椎动物漂流的强度急剧下降，漂流沿溪流的垂直分布变得相当均匀。白天水柱的照明水平与黄昏时期相对应。结果，鱼类变得越来越难以接近半水生吸热捕食者，白天无脊椎动物漂流的强度急剧下降，漂流沿溪流的垂直分布变得相当均匀。