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Study of the Sonoran Mud Turtle

Justin Congdon


Over the past 7 years (1990-1996), we conducted a mark-recapture study of Sonoran mud turtles in southeastern Arizona (van Loben Sels et al, 1997). The study areas are located at approximately 1,675 meters elevation in the Chiricahua Mountains and include the major drainages of West Turkey Creek and Rock Creek, their less permanent tributaries, and stock tanks (farm ponds) associated with both creeks.

Turtles are captured on land, by hand in shallow stream pools, or in deeper pools with dip nets, but the majority are captured in stock tanks (farm ponds) using baited hoop traps fitted with floats to prevent submergence during heavy rains. Turtles captured alive are marked with a unique sequence of notches filed in the marginal scutes of the carapace, and weighed. Radiographs of large bodied juvenile females and all other females are taken at each capture (with recapture intervals > 10 days). All turtles are returned to their capture locations.

To date 740 individuals have been marked and over 1,100 recaptures made. We have also taken 305 X-radiographs of gravid females and 251 of older juveniles and non-gravid females to establish clutch size, clutch frequency and minimum size and age at sexual maturity. Sex ratio of adults was 1 male to 1.3 females. Of the individuals captured alive, approximately 18% were juveniles, 36% adult males, and 46% adult females. Adult females averaged 129 mm CL (max = 217 mm) and 342 g body mass (max = 784 g). Adult males averaged 126 mm CL (max = 169 mm;) and 290 g body mass (max = 690 g). The largest individuals of both sexes are larger than those reported in other studies of Sonoran mud turtles in Arizona (Hulse 1982; Rosen; 1987)

Minimum age at sexual maturity (alpha) of females was 6 years and the smallest turtle that produced a clutch of eggs was 106 mm CL and weighed 150 g. Clutch size averaged 6.27 (SD = 2.03; minimum = 2, maximum = 11, n = 305 clutches) and was positively correlated with body size of females. Data from radiographs of gravid females captured at least twice during June and August provided direct evidence that a minimum of 23 % of females that reproduced in a given year produced two clutches of eggs. The minimum interval between clutches, determined by a change in clutch size between radiographs, was 20 days.

van Loben Sels, R. C., J. D. Congdon, and J. T. Austin. 1997. Life History and Ecology of the Sonoran Mud Turtle (Kinosternon sonoriense) in Southeastern Arizona: A Preliminary Report. Chelonian Conservation and Biology 2:338-344.

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