6533b872fe1ef96bd12d37ed

RESEARCH PRODUCT

Upstream migration activity of cyprinids and percids in a channel, monitored by a horizontal split-beam echosounder

subject

description

A 200 kHz digital echosounder (HTI) with two split-beam transducers was aimed horizontally to monitor the upstream migration activity of fish, from 24 April to 28 June, in Aijalansalmi channel (mean width 35 m, length 700 m, and maximum depth 5 m) from large mesotrophic Lake Paijanne to small eutrophic Lake Jyvasjarvi. This study was part of a larger project which aims to analyse the movement of commercially unimportant fish species and reduce the abundance of these fish in L. Jyvasjarvi. Catch samples were collected with a trap net located immediately upstream from the acoustic beams. The most common species in the catch were roach (Rutilus rutilus), perch (Perca fluviatilis), bream (Abramis brama), ruffe (Gymnocephalus cernuus), and white bream (Abramis bjoerkna). The upstream migration of fish was correlated with water temperature (r = 0.40) with time lag of 1 d. In spring, L. Jyvasjarvi warmed faster than L. Paijanne, causing spawning migration from L. Paijanne to L. Jyvasjarvi. Clear diurnal rhythm in activity was observed. The migration rate through the channel peaked around dawn and dusk. Catch per unit effort of the trap net suggested that the peak of the spawning migration of different species was separate. Upstream migration was induced by the temperature difference between two lakes, and the activity of the migration was regulated by temperature changes and light rhythm.