Impacts of human recreation and hydroelectric flow regime on basking behavior of Northern Map Turtles, Graptemys geographica

Abstract

Northern Map turtles, Graptemys geographica, are state endangered in Maryland and are found only on the Lower Susquehanna River and its tributaries. Human recreation and water level fluctuations from the Conowingo Dam potentially limit basking behavior in this population. Turtles rely on basking to thermoregulate; decreased basking activity can potentially decrease population viability. I quantified the effects of 1) recreational human disturbance and 2) rising water from the hydroelectric dam on basking behavior. While motor-powered boats were often ignored, turtles were most often disturbed by slow-moving vessels like kayaks. Habitat use changed with increasing water levels; the interaction between dam flow and tide level had the greatest effect on basking behavior. Basking activity typically decreased as available habitat decreased. These disturbances do restrict basking behavior and require immediate mitigation. Artificial basking platforms and seasonal boating regulations should be implemented. Preparations for testing artificial basking platforms have already begun.