No abstract

Weirs and dams are wide spread throughout the world's river systems. The most direct effect of these barriers is the limitation of organism movements, i.e., the alteration of connectivity by fragmentation of the aquatic habitat. Whereas the impact of fragmentation on migratory fish species has been well studied, insights on nonmigratory species are still needed. In particular, knowledge on the effects of dams on cyprinid populations at the watershed scale is lacking. Therefore, we studied the genetic structure of eleven chub (Squalius cephalus) samples lined up in the highly fragmented Durance River (France). Using five microsatellite loci, we show that even if the overall genetic differentiation is low, isolation by distance does occur and that genetic diversity increases from upstream to downstream. Dams seem to participate jointly with waterway distance in the explanation of this pattern. However more precise conclusions cannot be made. Guidance for future studies are given.

The European Habitat Directive encompasses a conservation policy devoted to conserve habitats rather than single species. This ambition has strong ecological justifications, and inspires other initiatives such as the IUCN red list of ecosystems. Evaluating this policy is therefore pivotal to identify and reproduce best practices. However, the habitat aspect of this policy has so far not been systematically assessed. To make up for this lacuna, we take advantage of decision‐aiding methodologies to introduce a new normative framework. According to this framework, a conservation policy is positively evaluated if it contributes to conservation, is science‐based, operational, and legitimate. Based on an exploration of the published literature and unpublished reports and databases, we identify knowledge gaps plaguing the European habitat conservation policy. We argue that, due to these knowledge gaps, the contribution of this policy to the conservation of habitats is unproven, it is not science‐based, not operational and not legitimate. Our study draws heavily on the French implementation. Analyzing this example, we highlight knowledge gaps that carry lessons for European conservation policies as a whole, but also for conservation initiatives focused on habitats in a broader geographical and political context. We then identify concrete means to strengthen habitats conservation policies.