EFFECTS OF REMOVAL AND REGENERATION OF BANKSIDE VEGETATION ON FISH POPULATION-DYNAMICS IN THE WARTA RIVER, POLAND

In March 1989 both banks of a 450 m section of the Warta River, 2 km a bove a reservoir, were cleared of their riparian vegetation (osiers, w illows and alders). In October 1988 17 fish species had been recorded there, with a standing crop (SC) of 31.9 kg ha(-1). In April 1989, the number of species decreased to 11, and their SC to 7.9 kg ha(-1). Ove r the next three years new alder trees appeared and osiers regrew to 3 .5 m. The SC in October 1990, October 1991 and May 1992 was recorded a t 36.5, 66.2 and 40.9 kg ha(-1), respectively. The primary effect was on phytophils, whose biomass was directly proportional to the height o f the trees and osiers (r = 0.87, p = 0.05). The litho-phytophils appe ared to occupy the habitat vacated by the phytophils soon after bank c learance (r = -0.87, p = 0.05), but then declined as the osiers grew.