Astakhov M.V.
В журнале Inland Water Biology
Год: 2023 Том: 16 Номер: 3 Страницы: 490–502
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.
