Inventory of Freshwater Turtles at Cape Cod National Seashore with Recommendations for Long-Term Monitoring

Cook, Robert; Boland, Kelly; Kot, Stanley; Borgmeyer, James; Schult, Matthew

Turtles comprise a familiar group of vertebrates that occupy a broad range of habitats and ecological functions. Some species are important in energy flow, and may dominate vertebrate biomass, particularly in aquatic habitats (Congdon et al. 1986). By virtue of their trophic position, biomass, and vulnerability to anthropogenic perturbations, reptiles can be important indicators of environmental quality (Gibbons and Stangel 1999). Due to their longevity and habits, turtles accumulate environmental contaminants and are ideal for monitoring their presence in aquatic environments (Golet and Haines 2001, Rie et al. 1999). Turtle populations appear to be declining throughout the United States, as well as globally, due to the combined impacts of habitat loss, degradation, and fragmentation, road kill, invasive species, pollution, disease, unsustainable harvest, and global climate change (Gibbons et al. 2000, Klemens 2000). Cape Cod National Seashore (CACO) supports populations of six species of non-marine turtles, occupying terrestrial, freshwater, and estuarine habitats. These include presently common and/or widespread species such as painted turtle (Chrysemys picta) and snapping turtle (Chelydra serpentina), the less common musk turtle (Sternotherus odoratus) and spotted turtle (Clemmys guttata), as well as the Massachusetts “threatened” northern diamondback terrapin (Malaclemmys t. terrapin), an estuarine species, and the terrestrial eastern box turtle (Terrapene c. carolina), a Massachusetts “special concern” species. Turtle communities composed of viable populations of native species are indicative of intact native habitats and landscape processes at CACO, but there are several agents of change operating that have the potential to affect the turtle community and its component species. These include land use and development adjacent to the park, fire suppression, water pollution, increased traffic, recreational use, and exploitation. Some of the mechanisms by which these agents can negatively affect turtle abundance, population structure, and distribution include: 1. Alteration of aquatic habitats through nutrient loading or changes in water level (groundwater withdrawal), salinity (tidal alterations), and plant communities (invasive plants and groundwater withdrawal); 2. Declines in food abundance due to pesticide use or changes in aquatic habitats; 3. Increased road kill as increasing local human population and visitation increases habitat fragmentation and traffic volume; 4. Increased predation of turtle nests by over abundant populations of native predators, i.e.“subsidized predators” such as raccoons (Procyon lotor); 5. Loss of open nesting sites for turtles as fire suppression alters patch dynamics and forest succession advances; and 6. Direct loss of animals to collection by visitors and poachers. Prior to this work, there was only general knowledge of the occurrence of aquatic turtles on outer Cape Cod (Lazell 1976, Jones 1992).