Spawning movements of European grayling Thymallus thymallus in the River Aisne (Belgium)

Abstract

In three consecutive years (1998 to 2000), 20 adult grayling Thymallus thymallus (L.) (FL +/- SD: 326 +/- 43 mm) were radio-tracked during circum reproduction period (February to May) in the River Aisne, Belgium. Before the spawning period, grayling remained consistently in the pool-riffle sequence in which they had been captured. Pre-spawning migration time extended from 7 to 29 March. Distances travelled during the spawning migration ranged from 70 to 4980 in (mean +/- S.E.: 1234 +/- 328 m). Spawning migrations stalled under conditions of decreasing water level and increasing water temperature in a thermal range (daily mean Tdegrees) from 5 to 8 degreesC. Spawners remained from 1 to 31 days (mean +/- S.D.: 10.4 +/- 9.8 days) at the spawning grounds and performed a post-spawning homing from 28 March to 18 April in decreasing water flow and in a thermal range (daily mean Tdegrees) from 7 to 11 degreesC. This study demonstrates that migration patterns of grayling are similar between years, but with a timing adjusted as a response to annual variations of the hydroclimatic conditions