Freshwater turtle climbing abilities: Implications for the design and use of shoreline erosion control structures

Abstract

Freshwater shoreline modifications can reduce connectivity between aquatic and terrestrial environments, contributing to the decline of freshwater biodiversity. Freshwater turtles may be particularly vulnerable to shoreline modifications because they must access land for essential activities such as nesting, basking, and dispersal. Here, we tested the clinging abilities of three freshwater turtle species (i.e., painted turtles, Chrysemys picta; eastern musk turtles, Sternotherus odoratus; and northern map turtles, Graptemys geographica) to inform design criteria for mitigating the impacts of shoreline modifications on the ability of turtles to perform these behaviours. We tested clinging behavior using a ramp and pulley system with smooth and rough concrete ramps to find the maximum clinging angle for all three species. We found that painted turtles were the weakest at clinging, averaging a maximum clinging angle of 37° on a smooth ramp and 73° on a rough ramp. Eastern musk turtles had an average maximum clinging angle of 45° on a smooth ramp and 87° on a rough ramp. Northern map turtles had an average maximum clinging angle of 41° on a smooth ramp and 87° on a rough ramp. For all three species, surface type had significant effects upon maximum clinging angles, and mass was also statistically significant in affecting the clinging of eastern musk and northern map turtles. As the painted turtles were the weakest clingers and the most ubiquitous species (Van Dijk, 2016), we used this species to validate the clinging trials through volitional climbing tests. Successful climbs peaked at 35° on the smooth ramps and 40° on the rough ramps. To maintain turtle accessibility in areas with these species, future shoreline modifications should be textured and not have slopes that exceed 40°.