The Blanding's Turtles (Emydoidea blandingii) of Weaver Dunes, Minnesota
Michael J. Pappas1, Bruce J. Brecke2, and Justin D. Congdon3
15 South Broadway, Rochester, Minnesota 55904 USA
Abstract: The population of Blanding's turtles (Emydoidea blandingii) at Weaver Dunes, Wabasha County, Minnesota, may be the largest in the world. The Weaver Dunes complex is composed of Weaver Bottoms which is a 1620 ha shallow lake, the old Zumbro River Channel (1500 ha consisting of approximately 750 ha of wetland habitats), and Weaver Dunes (600 ha of stabilized dunes). Between 15 April 1974 and 1 June 1980 we marked a total of 2402 individuals and made 474 recaptures. An additional 49 females were marked in June 1998 and 25 recaptures were made of previously marked individuals. Clutch sizes were determined for 44 females during 1976 and 1977 and 70 females during 1998. Adult females averaged 197.0 mm carapace length (CL) and 1.08 kg in body mass; adult males averaged 213.6 mm CL and 1.29 kg in body mass. Compared to males of similar length, plastrons of females were wider and total shell width was narrower and higher. Of 598 reproductive females, fewer than 20% were captured on land during the nesting season in successive years, and some females appeared not to reproduce each year. Clutch size averaged 9.8 eggs and was positively related to body size of females. Eggs averaged 23.5 by 37.5 mm in width and length, respectively, and hatchlings captured in the field averaged 33.1, 36.7, and 15.4 mm in plastron and carapace length and shell height, respectively. Females matured at a minimum CL of 160 mm and minimum age of 14 yrs. Juveniles averaged 10 mm/yr increase in CL. The oldest adults in the population were a minimum age of 40 to 45 yrs. Adult growth averaged 0.46 mm/yr, with some adults exhibiting zero or negative growth. Juveniles comprised 35.1-55.7 % of samples of turtles. Adult sex ratio was 1 male to 2.2 females. Emergence of adults from overwintering occurred between 13 March - 8 April. Nesting began between 26 May - 12 June, and nesting season duration averaged 17 days. Hatchling emergence averaged 27 days between mid-August and late September. Since 1.6% of hatchlings were captured on land in the spring following nest construction, some hatchlings apparently overwintered on land. First order estimates place the population size of Blanding's turtles at between 2500-4600 individuals on the west side of Weaver Dunes alone (the old Zumbro River Marsh area).
Keywords: Reptilia; Testudines; Emydidae; Emydoidea blandingii; turtle; ecology; growth; juveniles; morphology; population; demography; reproduction; sexual dimorphism; Minnesota; USA
SREL Reprint #2513
Pappas, M. J., B. J. Brecke, and J. D. Congdon. 2000. The Blanding's turtles (Emydoidea blandingii) of Weaver Dunes, Minnesota. Chelonian Conservation and Biology 3:557-568.