Identifying Suitable Turtle Overwintering Habitat Through the Integration of Thermal, Chemical and Physical Wetland Properties

Abstract

Turtles are among one of the most vulnerable vertebrates on the planet and within Canada, all eight native species of freshwater turtle are designated as at-risk under COSEWIC. The primary extinction risk turtles face is the loss of their habitats. At the northern limit of their range, turtles rely on the presence and persistence of aquatic habitats to survive the winter. In the face of unprecedented climate and land-use changes, identification of key overwintering habitat attributes is crucial because relatively little is known about how they interact to optimize overwintering habitat suitability. We measured in-situ thermal, chemical and physical conditions at Blanding’s turtle overwintering sites within wetlands in the Georgian Bay Biosphere Mnidoo Gamii to (1) characterize available overwintering habitat, (2) test for overwintering habitat selection by Blanding’s turtles and (3) quantify the turtle resilience zone (RZ). We measured water and sediment temperatures, dissolved oxygen (DO), water, ice and snow depth at 5 (2020-2021) and 19 (2021-2022) Blanding’s turtle overwintering locations and four paired available microhabitats (floating mat, inflow, lagg, open water) across 5 wetlands. Blanding’s turtles selected average daily temperatures that ranged from 3.58°C to 0.53°C with a mean of 1.08°C, minimum average DO observed was 1.10 mg/L and average water and ice depth ranged from 42cm to 79cm, 12cm to 38cm, respectively. Based on habitat use data, we quantified the RZ as present when aquatic habitats had temperatures between 0 and 4°C, DO ≥1 mg/L and minimum water depth of 40 cm. Using the RZ we identified suitable overwintering habitats within our study region and found that the RZ varied across wetlands and microhabitats. Overall, the RZ is a powerful tool that can be used to identify suitable overwintering sites which can directly contribute to conservation and management strategies for at-risk turtles.