The meso-habitat scale as a new approach for the conservation of the endangered crayfish Austropotamobius pallipes complex in Northern Italy

Meso-scale habitat models have been widely used in the context of water resources planning and management and demonstrated interesting potentials for the ecological management of mountainous streams in Northern Italy. In particular, the meso-habitat scale approach allows rivers to be surveyed for longer stretches and involves a large range of habitat descriptors. Native populations of the endangered Austropotamobius pallipes species complex had decreased markedly in the last decades due to habitat modification and the introduction of alien species. Five streams populated by Austropotamobius pallipes complex in the mountainous areas of Northern Italy were surveyed according to meso-scale habitat criteria and crayfish were sampled by night. A total of 156 mesohabitat or hydromorphologic units (HMUs, such as pool, riffle and rapid) were detected and 755 crayfish (398 females and 357 males) were collected by sampling each mapped HMU; their total (TL) and cephalothorax lengths (CL) were measured; and weight and occurrence of mutilations were recorded. High crayfish density affected significantly mutilation presence. Substrate features (as proportion of gravel and sand), shallow water depth and cover variables (as presence of boulders, woody debris and undercut banks) demonstrated high importance for the occurrence of crayfish at the mesohabitat scale. Understanding crayfish distribution related to habitat characteristics showed its effectiveness for the definition of conservation actions, environmental flow assessment and the design of habitat restoration measures.