Rehabilitation of brown trout, Salmo trutta, habitat damaged by riparian grazing in an English chalkstream.

Abstract

Rehabilitation trials involving riparian fencing and limited pool excavation were conducted on the River Piddle and Devil's Brook, Dorset, England, which had been degraded by intensive riparian grazing. In one trial, based on two short (94 and 99 m) treated sections and two control sections, brown trout, Salmo trutta L., numbers were monitored from 1994 (pre-treatment) to 2000. In a second trial from 1996 (pre-treatment) until 2000, trout numbers were monitored in 900 m and 1400 m treated sections. After rehabilitation, juvenile trout numbers increased in the two short sections (Trial 1) but fell in one of the long sections. Adult numbers also increased markedly in the two short-treated sections relative to the controls and they increased markedly in one of the long sections despite a reduction in juveniles. Marking of trout in the short sections showed that they selected the rehabilitated habitat in preference to the control habitat and that immigration was the main source of adult trout, as it must also have been in the 1400 m section. While the results indicate that improvements can be made to adult trout habitat, more research is required on the impact on juvenile production before the impact of such work on the true population can be established.