Impact of hydropeaking on the abundance of juvenile brown trout in a Pyrenean stream

Abstract

Many French rivers are concerned by hydropeaking management. Sudden flow variations cause disturbances of the aquatic environment, fish habitat being particularly affected. The abundance of the most sensitive life stages of brown trout (age groups 0+ and 1+) in the River Oriege (Pyrenees, France) were studied 330m upstream, and 700 and 3,000 m downstream of a hydroelectric power plant with hypolimnetic releases from a nearby high-altitude reservoir. The natural flow of the river was preserved when the plant was inoperative. Hydropeaking strongly reduced densities of young trout and disturbed their choice of mesohahitat 700 m below the plant, but such effects were attenuated 3,000 m downstream, mainly due to reduction of the slope. These results provide elements to assess the capacity of a regulated stream to support the early life stages of trout, and therefore the whole population.