Habitat Use by Western Pond Turtles in the Trinity River, California

Habitat associations of western pond turtles (Clemmys marmorata) were examined in a dammed and undammed tributary of the Trinity River in northwestern California to clarify the relations between habitat use and damming. The dammed tributary had more sedimentation, decreased water temperatures, increased canopy cover, and higher water velocities, all of which are potentially relevant to western pond turtles. The overall heterogeneity of aquatic habitats also was lower, possibly because of the dam. At both dammed and undammed sites, western pond turtles appeared to select for deep water with low velocities and the presence of underwater refugia. On the dammed tributary, western pond turtles were associated with basking structures, which may be particularly important because of the low water temperatures. On the undammed tributary, western pond turtles tended to be in slower-flowing portions of the river with denser canopy cover and higher water temperatures. Given the alterations of channel morphology and flow regimes associated with damming, the implications are that habitat suitability for western pond turtles is decreased. While damming may increase the amount of deep water along shores and promote formation of undercut banks, it eliminates low-velocity areas preferred by western pond turtles and lowers water temperatures. Habitat enhancement efforts should focus on restoring natural structural and hydrological features.