Abstract

Blanding’s turtles (Emydoidea blandingii), historically a common species in New York State, are now threatened. Population numbers of adults (16+ yr) are known to exist in two distinctly separate geographic locations in the state, and total approximately 600 individuals. In 1993 a plan was developed by the New York State Department of Environmental Conservation, Nature Conservancy, and Cornell University to further assess both of the populations and to use head starting as a strategy to enhance the population located in the southeastern part of the state. This strategy was selected because predation was known to be an important factor limiting immigration of hatchlings into the population. To date, two groups of turtles have been raised in captivity and released back into their natal nesting areas.

In the late summer and early fall of 1994 and 1995 turtles were brought into captivity 24–72 hr after hatching. They were housed in small groups of one to five individuals, and were fed two different commercially available aquatic turtle diets on a daily basis in 1994 and a single diet in 1995. Turtles were housed initially in plastic feeding troughs in 4–6 in of water and later in 30-gal aquaria which were both maintained at 78–82°F. Submerged filters were utilized to maintain water quality. Floating plastic plants provided hiding places for the turtles. Rocks were stacked in the tanks so as to allow for turtles to leave the water as desired, and incandescent lamps were used to stimulate natural basking behavior and were fixed at a 12/12 hr light/dark cycle. Full spectrum lighting was not used, and did not appear to be required for proper growth. Common problems associated with rapid growth in turtles, such as shell and long bone malformations were not observed.

Because of the high predation rate of free-ranging hatchling turtles, a target release size was predetermined based on previous field observations. At the same time, an effort was made to minimize the time the turtles were to be retained in captivity. Nine to 10 mo was required for turtles to reach the appropriate size. Preparation for release of the turtles included live prey trials to assure prey recognition, screening the turtles for selected infectious agents, gradually decreasing water temperatures, and conditioning the turtles to seasonal photoperiods.

For the first group of turtles, mass, carapace length, and width measurements were recorded regularly on all individuals. In addition, mid-line plastron length and height measurements were made starting shortly after the project began. Upon entering captivity in the fall of 1994, the average measurements of hatchling turtles in the first group were: mass: 9 g (range 8–10 g); carapace length: 36.8 mm (range 35.1–37.8 mm); width: 33.1 mm (range 32.0–34.4 mm). At release in the summer of 1995, average turtle measurements for this group were as follows: mass: 158 g (range 129–185 g); carapace length: 100.1 mm (range 90.1–106.3 mm); mid-line plastron length: 98.4 mm (range 91.5–103.9 mm); height 39.8 mm (range 36.0–43.0 mm); width: 76.2 mm (range 71.9–79.2 mm).

The following year, the mid-line plastron length of all turtles was measured regularly in addition to the other measurements listed above. Upon entering captivity in the fall of 1995, the average hatchling measurements for the second group of turtles were: mass: 9 g (range 8–11 g); maximum carapace length: 39.0 mm (range 34.8–41.8 mm); mid-line carapace length: 34.6 mm (range 31.3–37.7 mm); height: 16.0 mm (range 14.6–18.2 mm); width: 34.4 mm (range 32.5–36.0 mm). One month prior to release in the summer of 1996, average turtle measurements for this group were as follows: mass: 109 g (range 97–131 g); carapace length: 87.2 mm (range 82.5–94.7 mm); mid-line carapace length: 85.5 mm (range 80.0–92.9 mm); mid-line plastron length: 81.4 mm (range 76.7–89.2 mm); height: 35.1 mm (range 33.0–37.0 mm); width: 68.8 mm (range 66.2–72.1 mm). The slightly lower growth rate of this group is attributed to a more restricted caloric intake and food type, which was imposed because of concerns that turtles from the first group may have been fed excessive quantities of food at certain times during the 10-mo period in captivity.

Prior to this project, it was unclear how rapidly the turtles might grow in a 10–12-mo period. In this study, the size attained in 10 mo is comparable to that of 5–6-yr-old free-ranging Blanding’s turtles. Presently, it can be recommended that the morphometrics recorded in the 1995–1996 season be used as target parameters for future groups of Blanding’s turtles being raised within a similar time frame. Based on limited retrapping studies, survival rate appears to be high at 1 and 2 yr post-release.