Effects of a micro hydroelectric power plant upon population abundance, mobility and reproduction behaviour of European grayling T. thymallus and brown trout S. trutta in a salmonid river

This study examines the potential effects of a new micro hydroelectric power plant (MHPP) on
the behaviour (habitat use, movements) and population abundance of European grayling (T. thymallus) and
brown trout (S. trutta) in the Lhomme (Belgian Ardennes). Thirteen grayling and five brown trout were captured
before their spawning period and were manually radio-tracked up to 6 times a week. Population density
and biomass were estimated into two different sampling sectors with electric fishing, before and after the
MHPP started up. The mobility patterns of grayling and trout in the reach of the river Lhomme influenced by
the MHPP strongly contrasted with results obtained in an undisturbed river of the same type in the Belgian
Ardennes. Movements were mostly restricted and rarely increased during the spawning period. Spawning
took place, but was disturbed by hydropeakings. The population biomass of grayling and trout decreased by
61 % and 23 % respectively, five months after the start-up of the MHPP exploitation.