Do culverts impact the movements of the endangered white-clawed crayfish?

Culverts can impact the migration and dispersal of aquatic animals and result in population fragmentation, increasing the risk of local extinction for endangered species such as the white-clawed crayfish Austropotamobius pallipes. This study used radio telemetry and passive integrated transponder (PIT) telemetry to determine whether existing and experimental covered culverts affect the upstream and downstream movements of adult white-clawed crayfish. Daily crayfish movement rates did not differ significantly between an unlit 363-m long culvert and open stream channel sections. Crayfish moved into dark, covered sections volitionally. However, limited upstream movement occurred at sudden transitions of bed height or smooth-concrete box culvert sections with fast flow, suggesting partial barrier effects. In the 20-m long experimental in-stream culvert, also dark, but with natural stream bed, 70% of radio-tagged crayfish released downstream entered the culvert, as did 60% of those released upstream. Overall 35% passed through, with similar numbers in each direction. We conclude that dark culverts up to several hundred metres do not inhibit dispersal of white-clawed crayfish, provided stream slope, bed type and water velocity are amenable for movement and refuge. Care is required to ensure that culverts are bioengineered to ensure that average water velocity is sufficiently low and local hydraulic variation high, the bed and/or sidewalls contain refuge structures, and there are no cross-channel steps in bed level. Smooth-bedded box culverts are unlikely to be suitable for white-clawed crayfish. Les petits ponts d’une seule travée peuvent influer sur la migration et la dispersion des animaux aquatiques et entraîner la fragmentation de la population, augmentant le risque d’extinction locale des espèces menacées telles que l’écrevisse à pattes blanches, Austropotamobius pallipes. Cette étude a utilisé la télémétrie radio et la télémétrie par transpondeur passif intégré (PIT) afin de déterminer si les ponceaux couverts existants et expérimentaux affectent les mouvements en amont et en aval de l’écrevisse à pattes blanches adulte. La vitesse de déplacement des écrevisses ne diffère pas significativement entre un long ponceau fermé de 363 m et des sections de canaux ouverts. Les écrevisses se déplacent de leur propre gré dans les zones sombres couvertes. Cependant, un mouvement réduit vers l’amont intervient au niveau des transitions soudaines de la hauteur du lit ou