Legacy effects of land cover and land use on painted turtle (Chrysemys picta) populations over a 20-year period in southeastern New Hampshire

More than half of all freshwater turtles and tortoises are threatened with extinction. Human land use practices and land cover conversion often decrease adult turtle survivorship and dampen the reproductive potential of turtle populations. The ability to make informed conservation and management decisions depends on understanding the relative impacts of different landscape contexts on turtle populations, and the spatial extent over which they have an impact. We surveyed painted turtle (Chrysemys picta) populations along an urbanization gradient in southeastern New Hampshire, USA to assess the relative impact of land cover, land use, and chemical contaminants on population density and sex ratio. We compared the findings from our comprehensive field surveys (2019-2021; “modern”) to earlier surveys (2001-2001; “historic”) conducted at identical and nearby ponds. In both time periods, population density increased with proportion of wetland and decreased with forest cover. Modern turtle density was best explained by historic land cover suggesting a lag between land cover change and a detectable impact on the population. Modern road length negatively influenced modern population density whereas historic road length did not have a measurable impact on density at that time. In both time periods we found increased forest cover associated with male-skewed populations. We tested 30 painted turtle blood sampled for 63 chemical contaminants. Organochlorine pesticides and synthetic pyrethroids were pervasive in turtle blood but not detected in water samples suggesting these chemicals are bioaccumulating in turtles despite low environmental concentrations. Our findings illustrate that effective management of turtle populations requires consideration of legacy effects of land use and land cover conversion as well as direct sources of mortality.