Species loss and shifting population structure of freshwater turtles despite habitat protection

Changes to population and community structure can have important ecological consequences and raise conservation concerns when causes are anthropogenic; however, signs of stress may not always be apparent. Turtles are long-lived and presence of adults may suggest healthy populations when lack of recruitment is actually threatening persistence. We observed and captured turtles for two years in Point Pelee National Park, Ontario, Canada, and compared our results with those collected 30 years earlier to determine if (1) species relative abundance, (2) sex ratios, and (3) age structure changed over three decades. Extirpation of the spotted turtle since 1972–1973 has altered the park’s species assemblage. Evidence also suggests that Blanding’s turtles have declined. Sex ratios were similar between time periods for all species except for the painted turtle which has become significantly more male-biased. Size structure for Blanding’s and snapping turtles shifted towards larger and presumably older age classes. Our results suggest that limited juvenile recruitment caused the size shift. Heavy predation on turtle nests from a dense raccoon population appears to be the main factor limiting recruitment. Despite protecting a sizable fragment of turtle habitat for a century, Point Pelee has lost one species and only one other species has a large healthy population. Our study illustrates that habitat protection provides no guarantee for species persistence when multiple threats exist and highlights the necessity for monitoring populations of long-lived species.