Using Spatial Approaches to Examine Threats Facing Common Snapping Turtles (Chelydra Serpentina) in the Urbanized Cootes Paradise Marsh, Lake Ontario

Abstract

In Ontario, the common snapping turtle, Chelydra serpentina, is listed as Special Concern and is at risk of decline. These long-lived organisms are particularly susceptible to anthropogenic threats owing to delayed sexual maturity, low recruitment and reliance on low adult mortality. Threats facing this species include road mortality and habitat loss and/or destruction. These threats are anecdotally evident within Cootes Paradise Marsh, a highly urbanized river-mouth coastal marsh located in a heavily urbanized region at the western end of Lake Ontario. Straddling Dundas and Hamilton, the wetland is bisected by Cootes Drive, a four-lane highway (maximum speed 80 km/h) that has resulted in fatal collisions with wildlife. We re-analyzed data from previous capture-mark-recapture studies and determined that the snapping turtle population has declined by almost 90% from 1985 to 2002. Using road mortality survey data collected by citizen science group Dundas Turtle Watch, we determined that some of this decline can be attributed to road mortality. Through radio tracking, we also found that the population remains at risk to road mortalities because their home ranges overlap surrounding roads. Besides the direct negative effect of mortality, roads impart broader and additional unintended consequences by hindering turtles’ access to critical nesting and overwintering habitat. We acquired digital orthophotos to assess changes in availability of nesting habitat, which is crucial for recruitment and population maintenance. Potential nesting habitat decreased by almost 50% between 1934 and 2010. Through nest surveys conducted in 2017, we determined that there is currently disproportionate use of artificial gravel mounds for nesting. For overwintering purposes, snapping turtles appear to be using a wide range of habitat types within the upland terrestrial matrix of the wetland ecosystem. We also confirmed that sites used for overwintering did not cool below inhibiting temperatures between early December and end of March. This study illustrates the toll that road mortality can have on urbanized herpetofauna populations and highlights the importance of ensuring that recovery plans focus on restoring both the quantity and quality of nesting and overwintering habitats.