Blanding's turtle COSEWIC assessment and status report: chapter 2
The Blanding’s Turtle, Emydoidea blandingii, is a medium-sized freshwater turtle largely confined to the Great Lakes Basin. In addition to lakes, it inhabits both permanent and temporary ponds, streams, and wetlands. Blanding’s Turtle is the only representative of the genus Emydoidea in the family Emydidae. The upper shell (carapace) is domed and smooth and may be up to 27.4 cm in length. The carapace is characterized by a grayish-black colour with tan to yellow spots or flecks scattered at random. The markings tend to get smaller and may fade altogether as the turtle ages. The lower shell (plastron) is a rich yellow and each scute (section) has a black blotch in the outer posterior corner. The plastron is hinged so that some individuals can completely close their shell. Males have a concave plastron, to facilitate copulation, whereas the female’s plastron is flat. Adults of both sexes have a bright yellow lower jaw and throat, and this is the species’ most characteristic feature.
In its Canadian range, the Great Lakes/St. Lawrence population of the Blanding’s Turtle is located throughout southern and south-central Ontario as far northwest as the Chippewa River in Algoma West, continuing eastward across the province into extreme south-western Québec. However, the Ontario distribution is not continuous and there are gaps in the Bruce Peninsula and surrounding areas to the south and southwest. As well, this species does not occur in the extreme southeast portion of the province and some areas north of Lake Ontario. The population in Québec appears to be concentrated around Gatineau Park and adjacent areas, close to the southwest boundary of the province along the north shore of the Ottawa River.
A small disjunct population occurs in Nova Scotia at the northeast periphery of the species’ range. The Nova Scotia population is the most isolated population in the species’ entire range. Blanding’s Turtle’s known range in Nova Scotia is limited to two watersheds in the central southwest portion of the province. At least three distinct sub-populations are recognized within the Nova Scotia population complex. One occurs in a protected area, Kejimkujik National Park, and the other two are in working landscapes outside of the park. These subpopulations are genetically distinguishable, with limited gene flow among them (~1.8 - 5.8 migrants per generation).
In the United States, the Blanding’s Turtle’s range occurs in the northern states, from Nebraska eastward to Ohio and Michigan and south to Missouri. There are also small local populations in New York, Massachusetts, New Hampshire, and Maine. The U.S. populations are often separated by natural barriers including large bodies of water such as the Great Lakes, and by artificial barriers including residential areas, commercial development, and major highways.
In Nova Scotia, the Blanding’s Turtle tends to prefer darkly coloured water indicative of relatively higher secondary productivity. However, this is not necessarily true in the Great Lakes/St. Lawrence population, where Blanding’s Turtles are often observed using clear water, eutrophic habitats. An individual turtle may use several connected lakes, rivers, streams, marshes, or ponds and travel upwards of 6760m in an active season. Turtles of all ages occur primarily in shallow water, with adults and juveniles showing slightly different habitat preferences. Adults are generally found in open or partially vegetated sites, whereas juveniles are more reclusive by nature and prefer areas that contain thick aquatic vegetation including sphagnum, water lilies and algae. The Blanding’s Turtle nests in a variety of loose substrates including sand, organic soil, gravel and cobblestone. Overwintering occurs in permanent pools that average about one metre in depth, or in slow flowing streams. Hatchling turtles may be able to withstand temporary freezing, as they have been noted to spend the night terrestrially upon emerging from their nests in late October and early September, and may possibly be terrestrial during their first winter.
Female Blanding’s Turtles mature between 14 and 25 years of age. Upon reaching maturity, adult females produce a maximum of one clutch per year of 3 to 19 eggs, but often less frequently, until 75+ years of age. Adult and juvenile Blanding’s Turtles have a narrow thermal tolerance, and perhaps because of this, bask regularly. The embryos also have a narrow thermal tolerance; eggs incubated below 22°C or above 32°C will not develop properly. The Blanding’s Turtle exhibits temperature sex determination, and eggs incubated at or below 28°C will produce males, while eggs incubated above 29°C will produce females. Eggs are laid in June, with hatchlings emerging in late September and early October. The cool Canadian climate results in a short active season, which limits nest success. Temperatures often fall below the minimum required for normal development or before full development can be completed. The Blanding’s Turtle is an exceptionally long-lived and late-maturing species, even for a turtle. Maturation in Canadian populations may be as late as 25 years, and turtles can survive in the wild in excess of 75 years. These life-history traits combined with a small reproductive output and concomitant low recruitment makes this species vulnerable to even tiny increases (<5%) in annual mortality of adults.
Population Sizes and Trends
The size of the Great Lakes/St. Lawrence population of Blanding’s Turtle is impossible to estimate accurately. Rough estimates suggest there could be about 10 000 individuals. However, this is an extremely crude guess. The population size in Québec has not been estimated, but evidence suggests that it is extremely small. These turtles live at low densities, perhaps at densities of less than one adult per km2, and populations are often isolated from one another. Monitoring of trends in habitat loss, and of population trends from other regions, indicates that the Great Lakes/St. Lawrence populations are probably declining because of ongoing loss and fragmentation of habitat.
In Nova Scotia, the well-studied population in Kejimkujik National Park shows very late maturity (20-25 years), great longevity (over 70 years), small clutch size (mean=11 eggs), and poor nest success (less than 50%). This population has declined due to habitat alteration, collection, road mortality, and other anthropogenic causes. A recent population viability analysis identified an alarming decline in the Kejimkujik National Park population. This analysis, based on survivorship and reproductive data from the population, has suggested that management actions are necessary to reverse the decline. Currently, it is estimated that there are only 210-245 adults in Nova Scotia.
Models based on demographic data from a long-term study on Blanding’s Turtle populations in Michigan indicate that population stability of such a long-lived, late-maturing species requires an annual juvenile (ages 2-14 years) survivorship of at least 76%, and an annual adult survivorship of at least 96%. It is likely that Canadian populations require even higher annual survivorship to maintain numbers because they experience even later maturity than the Michigan turtles.
Limiting Factors and Threats
Nest predation by raccoons, skunks, foxes and coyotes is the most significant cause of nest failure. There are few predators of mature turtles as their carapace strength and overall size deters or prevents most predation attempts. Cool summer temperatures may also increase the rate of nest failure, and result in the production of less viable hatchlings. A recently discovered source of nest failure is depredation by sarcophagid fly larvae. Additionally, in Nova Scotia, many nests are laid on lakeshore cobblestone beaches and are susceptible to flooding during wet years.
Development of wetlands and their surrounding areas significantly reduces the amount of available and suitable adult and juvenile habitat, and destroys potential and existing nesting habitat. Females are attracted to the gravel shoulders of roadways for suitable nesting habitat. This increases the risk of mortality to nesting females, as well as emerging hatchlings, as they are often struck and killed by vehicles.
The pronounced yellow chin and throat of the Blanding’s Turtle contribute to its overall beauty. Unfortunately, being one of the more colourful and personable species of turtles has made it sought after in the pet trade. Captive bred yearling Blanding’s Turtles are advertised in the United States for a relatively high price for a single specimen making the potential financial windfall very appealing to those who are willing to catch and sell turtles illegally. Most often adults are taken from the wild because they are easier to locate and catch, as well as being worth more in the pet trade. Removal of individuals from the reproducing population is a severe risk to the survival of long-lived species, as fluctuations in adult survivorship have a great impact on population stability.
Special Significance of the Species
The Blanding’s Turtle is the only representative of the genus Emydoidea. It has one of the smallest global ranges of any North American turtle. A large portion of its global range (20%) is contained within southern and south-central Ontario and the extreme southwest edge of Québec. With Ontario and Quebec containing such a large portion of the global range of this species, these provinces have a significant responsibility towards the conservation of this species.
The Nova Scotia population has been the object of intensive study since 1987, and has provided important data on demography and life history of this long-lived species. The isolated Nova Scotia Blanding’s Turtle populations havediverged genetically from populations in the main range, and contain a high degree of genetic variation and distinctness, and are therefore likely an important evolutionary component of the species.
The Blanding’s Turtle has been a “poster” species for conservation in Nova Scotia, Québec, Michigan, Wisconsin, Minnesota, and other jurisdictions. The species has also been important in theoretical studies; for example as the subject of the longest running study of turtle populations (at the E.S George Reserve in Michigan), where it has been used to test hypotheses of aging and hence is of great interest in gerontology.
The population of Blanding’s Turtles in Nova Scotia was designated by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) in 1993 as Threatened, and was designated Endangered by Nova Scotia in 2000. The Ontario population has been listed as Threatened in 2004, on the recommendation of the Committee on the Status of Species at Risk in Ontario (COSSARO). Habitat protection is afforded under the Ontario Provincial Policy statement of the planning act, and this species is also featured in Ontario’s forest management planning process. In Québec, Blanding’s Turtle has been ranked S1 by NatureServe Québec, and the Quebec Provincial Advisory Committee recommended a status of Threatened in 2003, with listing expected in 2006.
Blanding’s Turtle is listed by NatureServe as being at risk in 15 of 16 states that it inhabits in the United States. It is Extirpated (SX) from Rhode Island, Critically Imperiled (S1) in 3 states, Imperiled (S2) in 6 states, Vulnerable (S3) in 5 states, and Secure (S4) only in Nebraska.
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