Amphibians under threat: effects of dams on frogs and toads

Posted on December 28, 2013

Dams act as physical barriers to the movements of stream biota and stabilize the downstream flow regime, to the detriment of migratory species and those adapted to the intermittent flooding of backwaters and riparian areas. Negative impacts of dams on the diversity and abundance of river plants, macroinvertebrates and fish have been recorded, but relatively few studies have been carried out with amphibians. Working at 42 riparian sites along the Broad – Pacolet River in southern California, researchers conducted acoustic surveys of calling frogs and toads in spring, summer and winter and characterised the landscape surrounding each site. They also recorded the upstream and downstream distance from each site to the nearest dam: these distances ranged from less than 300 m to over 47 km. In the case of six of the nine frog and toad species examined, average abundance and/or the frequency of site occupancy increased with the distance downstream from the nearest dam, but in no case was abundance or occupancy related to the upstream distance to a dam. This finding suggests that a dam’s downstream environmental impacts (i.e., those predominantly related to flow regulation) were more influential than its upstream effects (i.e., those related mainly to habitat fragmentation).

Reference: Eskew, E.A., Price, S.J. & Dorcas, M.E. 2012. Effects of river-flow regulation on anuran occupancy and abundance in riparian zones. Conservation Biology 26 (3), 504–512.