Status of turtle populations in Point Pelee National Park

Abstract

Loss of biodiversity has been an irrepressible consequence of growing human populations and resource use. Some groups, such as turtles, are especially vulnerable because of their natural history. Turtles are threatened by habitat loss, population isolation, subsidized predators, road mortality, collection as pets, interactions with exotic species, human recreation, disease, and effects of contaminants. Parks are playing an increasingly important role of conserving natural habitats and populations in a mosaic of human development. Point Pelee National Park was historically the location of greatest turtle diversity in Canada. Recently, park staff and researchers have been concerned regarding population declines and possible extirpation for a number of the turtle species found at Point Pelee. My objectives were to determine species present, their population sizes and structure, and to examine possible causes of decline. I used mark-recapture to determine the population sizes and population structure of turtle species present. Captured turtles were marked, measured, sexed, and released at the site of capture. I compared my data to 1972 data on turtles at Point Pelee. I searched for turtle nests during the nesting season (late May to early July) in 2001 and 2002. Nests were randomly assigned to either a predation or a contaminant study. I monitored nests in the predation study to compare predation rates among species and areas. Predator surveys were also conducted along roadsides. Nests in the contaminant study were protected from mammalian predation to examine hatching success and three eggs per nest were collected for contaminant analysis. Nests of turtles designated as ‘species at risk’ were protected but not included in the predation or contaminant study. I examined nest protection effectiveness by comparing predation rates on protected and unprotected nests. Turtles killed by vehicles were recorded and models were created to predict the potential effects of road mortality and nest predation on turtle populations. I marked 1599 turtles (867 painted, 441 snapping, 95 Blanding’s, 172 map, and 24 stinkpot) from 5 May 2001 to 22 August 2002. Two spiny softshells and 3 red-eared sliders were observed. No spotted turtles were observed during this study. Blanding’s and snapping turtles have experienced a clear shift towards larger size classes since 1972, which suggests juvenile recruitment into these populations is limited. I found 178 turtle nests in 2001/2002. Predation rates on nests ranged from 62.5 % to 100 % among areas. Raccoon relative abundance was greatest along park roadsides. Hatching success was significantly lower in contaminated areas compared to other sites. Nest protection methods were highly effective in preventing mammalian predation. Road mortality models suggested that road mortality alone could cause population declines in Blanding’s turtles but not likely in snapping and painted populations. However, high nest predation levels are a much more serious risk to these populations. High nest predation of 70 % predicted serious declines in Blanding’s populations but not snapping and painted populations. However, predation rates of 90 % cannot be sustained by any species. Despite the short duration of this study, substantial evidence suggests that several serious threats to turtle conservation exist at Point Pelee National Park. Of seven native turtle species historically recorded at Point Pelee, six remain extant; but only one has a large healthy population. High levels of nest predation have limited recruitment, causing a shift in age structure. The present community is slightly less diverse than historically, and threats to all species conservation are apparent. Turtle populations at Point Pelee, like many other turtles worldwide, are imperiled by a multitude of threats.