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This study aimed to set out a new methodology for habitat modeling in high-gradient streams. The methodology is based on the mesoscale approach of the MesoHABSIM simulation system and can support the definition and assessment of environmental flow and habitat restoration measures. Data from 40 study sites located within the mountainous areas of the Valle d'Aosta, Piemonte and Liguria regions (Northwest Italy) were used in the analysis. To adapt MesoHABSIM to high-gradient streams, we first modified the data collection strategy to address the challenging conditions of surveys by using GIS and mobile mapping techniques. Secondly, we built habitat suitability models at a regional scale to enable their transferability among different streams with different morphologies. Thirdly, due to the absence of stream gauges in headwaters, we proposed a possible way to simulate flow time series and, therefore, generate habitat time series. The resulting method was evaluated in terms of time expenditure for field data collection and habitat-modeling potentials, and it represents a specific improvement of the MesoHABSIM system for habitat modeling in high-gradient streams, where other commonly used methodologies can be unsuitable. Through its application at several study sites, the proposed methodology adapted well to high-gradient streams and allowed the: (1) definition of fish habitat requirements for many streams simultaneously, (2) modeling of habitat variation over a range of discharges, and (3) determination of environmental standards for mountainous watercourses.

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Information was gathered on the distribution of white-clawed crayfish Austropotamobius pallipes complex in the watercourses of the Alessandria province (NW Italy), on the biological and ecological preferences of the species, and on the features of the biotopes in which it is found. A total of 409 sites on 361 watercourses connected to the main sub-basins of the Po River were analysed, with data gathered during the field research phase, conducted for three consecutive summers from 2002 through 2004. Thirteen percent of the sites investigated were found to currently house crayfish populations. The persistence in time of superficial water and natural morphology of the watercourse were found to be the chief requirements for the presence of crayfish. Data on land use, human density and other factors which potentially limit the survival of crayfish populations were also analysed. Key-words:Austropotamobius pallipes complex, freshwater crayfish, bio-ecological characteristics. STATUT DU COMPLEXE D'ESPACE D'AUSTROPOTAMOBIUS PALLIPES DANS LES COURS D'EAU DE LA PROVINCE D'ALESSANDRIA (ITALIE NORD-OCCIDENTALE) RÉSUMÉLe projet de recherche a prévu la récolte d'informations sur la répartition du complexe d'espèce Austropotamobius pallipes dans les réseaux hydrographiques de la province d'Alessandria (Italie nord-occidental), sur les caractères bio-écologiques de l'espèce et sur les caractéristiques des milieux où elle a été trouvée. Les prospections de terrain ont été faites durant trois étés consécutifs de la période 2002-2004 et ont permis d'analyser 409 sites sur 361 cours d'eau, appartenant aux principaux sous-bassins du fleuve Pô. Des populations d'écrevisses n'ont été trouvées que dans 13 % des sites prospectés. La persistance temporelle des débits hydriques superficiels et la morphologie naturelle constituent la condition essentielle pour la présence des écrevisses. En outre, les données

Genetic studies on the populations of Austropotamobius pallipes complex from Alessandria province (N-Italy), conducted on the basis of variations recorded in the sequences of mitochondrial DNA in the gene 16S RNA, have allowed to single out an overlapping zone of the distribution areas of the two taxa pallipes and italicus. In the crayfishes from a creek where both species have been ascertained to be present, the authors have applied the same molecular marker in order to investigate the distribution of the two taxa, stressing the syntopy of A. pallipes and A. italicus. Multivariate statistical techniques on 21 morphological parameters have been used in order to single out possible distinctive features of 31 crayfishes collected in this site, and of 225 crayfishes obtained from four sites in neighbouring areas. The results confirm the presence of a high morphological variability, not only at interspecific, but also at intraspecific level, which does not allow to distinguish the two species on the basis of the features measured in the present study. Key-words:Austropotamobius pallipes, Austropotamobius italicus, mitochondrial DNA, morphometry. SYNTOPIE DE A. PALLIPES ET A. ITALICUS: INVESTIGATIONS GÉNÉTIQUES ET MORPHOMETRIQUES RÉSUMÉLes études génétiques menées sur les populations du complexe d'Austropotamobius pallipes dans la province d'Alessandria (N-Italie) ont été faites sur la base des variations mesurées dans les séquences de l'ADN mitochondrial dans le gène 16S ARN. Elles ont permis de mettre en évidence une zone de superposition des distributions des deux taxa pallipes et italicus. On a utilisé le même marqueur moléculaire sur les deux espèces d'écrevisses provenant du même petit ruisseau, pour étudier leurs distributions et mettre en évidence la syntopie de A. pallipes et A. italicus. Des analyses statistiques multivariées ont été appliquées sur 21 paramètres morphologiques pour mettre en relief de possibles caractéristiques distinctives sur 31 écrevisses capturées dans ce ruisseau et

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