Drift of stoneflies in rivers of the European North of Russia

Abstract

Drift of stoneflies in a tributary of the Pechora, the largest river in the European Northeast of Russia, and in the Varzuga salmon river, Kolsky Peninsula, was studied. The highest densities of stonefly larvae in the drift were observed in spring (mature larvae drifting) as well as in late summer to early autumn (juvenile larvae and mature larvae of species emerging in autumn). Minimal drift values were observed in summer and in winter when the rivers were covered with ice. For stonefly larvae, pronounced night–day migratory dynamics are typical. A comparison between species composition of stonefly larvae in the stomachs of juvenile grayling and their composition in the benthos and drift during night and day was conducted. There is a disparity between the quantitative composition of species in drift and in fish stomachs. For juvenile grayling, an active selection of bottom organisms is typical. The largest mature larvae of Leuctra fusca were more abundant in grayling diets than in the drift.