Management of the white-clawed crayfish (Austropotamobius pallipes) in Western France: Abiotic and biotic factors study

In France, the distribution of the white-clawed crayfish, Austropotamobius pallipes (Lereboullet, 1858), is restricted, fragmented and mainly located in headwaters. To preserve this indigenous species, it is necessary to characterize its ecological requirements (water and habitat quality). With this aim in view, a two-year study is being conducted in the Deux-Sevres department (Western France) since November 2002. Nine brooks from four different catchments are monitored regularly; eight of the nine brooks harbour white-clawed crayfish populations. Two sampling sites are surveyed per brook, the first being where the crayfish population is located and the second 2 to 3 km downstream. Physicochemical parameters (18) are measured twice monthly and biotic factors are estimated twice yearly. In this study, the I.B.G.N. (Indice Biologique Global Normalise) protocol based on the determination of macroinvertebrates was used as a biotic index of biological water quality. Results of this preliminary study on two brooks (Thouet and Verdonniere) show that physico-chemical and biological data considered separately do not provide reliable information about A. pallipes ecological requirements. However, the use of multivariate analyses (Principal Component Analysis) to combine abiotic and biotic factors highlights a good correlation between these parameters. Organic matter appears to be a better discriminating factor than mineral matter affecting presence or absence of the white-clawed crayfish.