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ABSTRACT1. In France, the distribution of the native white-clawed crayfish (Austropotamobius pallipes) is restricted, fragmented and mainly located in headwater streams. To conserve this indigenous species, it is necessary to characterize its habitat preferences.2. Seven brooks in the Deux-Se`vres De´partement (western France) containing wild populations of A. pallipes were studied to determine its ranges of tolerance to 19 physical and chemical water parameters. On two brooks, the Se`vre Nantaise and the Verdonnie`re, sites with and without A. pallipes were compared. Each site was sampled twice monthly from November 2002 to November 2004.3. It was found that the white-clawed crayfish was able to tolerate wide ranges of values of some of the measured parameters. The Magot site harboured the largest A. pallipes population (17.5 crayfish m À2 ) and had dissolved oxygen concentrations as low as 4.93 mg L À1 , while water temperature rose above 208C for several consecutive days during summer and nitrate concentrations were always found to be above 30 mg L À1. These unusual findings could call into question the status of A. pallipes as a bioindicator of good water quality.4. Principal component analyses (PCA) suggested that an increase of organic matter was a discriminant factor for the presence or absence of A. pallipes. In addition, sites with and without crayfish on the Se`vre Nantaise brook showed showed significant differences (p50:05) in total organic carbon (TOC), and those on the Verdonnie`re brook in turbidity and total suspended solids (TSS).

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Any initiative aimed at the management of a threatened species needs a good knowledge of its environmental requirements. Aims of this study were to individuate suitable areas for the reintroduction of crayfish species belonging to the Austropotamobius pallipes complex and to evaluate the causes of the local extinction in Tuscany (Italy) of some populations. Between May 2003 and September 2004, we collected ecological data from 19 streams of 4 catchments, 9 watercourses where crayfish were present (WI) and 10 where they were present in the recent past and absent now (WO), and we compared them. Multivariate analyses were performed using chemico-physical and biotic parameters to examine the relationships between their values and the presence of crayfish. The results did not allow us to find significant differences between the two categories of streams, suggesting their suitability for crayfish reintroduction. Key-words:Austropotamobius pallipes complex, Extended Biotic Index (IBE), Fluvial Functionality Index (IFF), biotic and abiotic parameters. Bull. Fr. Pêche Piscic. (2006) 380-381 : 1095-1114 -1096 -hydrographiques différents, qui abritent actuellement des écrevisses (WI) ou qui en sont dépourvus depuis peu (WO). Des analyses multivariées ont été réalisées en prenant en compte à la fois les paramètres physico-chimiques et biotiques afin d'examiner les relations entre ces données et la présence du complexe Austropotamobius pallipes. Les résultats ne montrent pas de différence significative entre les deux catégories de ruisseaux ce qui traduirait l'aptitude des sites WO à accueillir des écrevisses. CARACTÉRISATION ÉCOLOGIQUE DE RUISSEAUX TOSCANS (ITALIE) POUR LA GESTION DE L'ÉCREVISSE MENACÉE AUSTROPOTAMOBIUS PALLIPES