| dc.description.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. | |
