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Individual study: Effects of penning on site fidelity and movements of translocated gopher tortoises Gopherus plyphemus, Savannah River, South Carolina, USA

Published source details

Tuberville T.D., Clark E.E., Buhlmann K.A., Gibbons J.W., , , & (2005) Translocation as a conservation tool: site fidelity and movement of repatriated gopher tortoises (Gopherus plyphemus). Animal Conservation, 8, 349-358

Summary

Translocation is an important means of conservation management, but success is generally low, particularly for non-game species. Compared to birds and mammals, very little research has been conducted on translocation of amphibians and reptiles, and the success rate is often much lower. Nevertheless, with two-thirds of the world's tortoise and freshwater turtle species at risk, translocation may be one of the few remaining options for re-establishing extirpated populations and reconnecting fragmented ones. One of the primary concerns associated with translocation projects, is the extent to which repatriated species remain site faithful. Here, a study is described in which the effects of temporary outdoor enclosures and penning duration on site fidelity and movements of gopher tortoises Gopherus plyphemus were assessed.

Tortoise translocation: A total of 74 gopher tortoises Gopherus plyphemus (including adults, subadults and juveniles) were obtained from a 40 ha industrial development site in southeast Georgia (USA) during August-October 2001. Tortoises were captured using pitfall traps at burrow entrances, or by manual excavation of burrows. In addition, 32 tortoises were hatched in captivity from eggs found in the field. All the tortoises were transported to an area of open-canopy longleaf pine, flanked by floodplain sweetgum Liquidambar stytaciflua forest along the Savannah River in Aitken County, South Carolina.

Experimental release pens: Three separate arrays of artificial tortoise burrows were created, one used to pen tortoises for nine months, one used for 12 month penning and one in which tortoises were not penned. Burrows were created using a gas-powered auger with a 46 cm bit placed at a 30º angle. Each array comprised of 24 burrows, one metre in length, extending outwards from a hub in six directions to 50 m. The two arrays used for penning were enclosed by 92 cm tall aluminium flashing buried approximately 30 cm into the ground and reinforced with wooden stakes.

Releases: Tortoises penned for nine months were released on the 8 July 2002, tortoises penned for 12 months were released on the 23 September 2002 and those not penned released between the 29 March and 3 April 2002. All treatments comprised 12 or 13 adults and only data on adults is presented in the study. Prior to penning or release, tortoises were kept in an offsite holding area.

Post-release monitoring: Tortoises were monitored by fitting two radio-transmitters, mounted one either side of the rear of the carapace. Following release, individuals were monitored daily through October 2002, about weekly from November 2002, and then 2-3 times per week from March-October 2003. Tortoises travelling more than 1 km from the release site without establishing a burrow were considered to have dispersed from the release site. Activity areas were also defined in both years, by calculating minimum convex polygons based on all points where individuals were located.

Site fidelity: Site fidelity varied significantly amongst penning treatments during year one, with those penned for longer remaining more site faithful. In year two penning had no effect on the degree of fidelity regardless of whether all animals were considered or only those that did not disperse in year one. The effects of penning on fidelity are shown in Table 1 (attached). Tortoises dispersing in year one were retrieved, but four were lost from the study within 15 days of release, presumably because they travelled out of signal range between daily tracking periods.

Activity: In year one, activity areas varied significantly between penning treatments. Year one activity areas were significantly smaller for the 12-months penning treatment (1.96 ± 1.07 ha) than either no-penning (93.54 ± 33.43 ha) or 9-month penning (37.06 ± 14.08 ha). The activity areas of individuals penned for 9-months did not significantly differ from those that were not penned. Year 2 activity areas did not differ significantly between penning treatments, regardless of whether or not animals that attempted to disperse in year one were considered. Overall, activity areas were smaller in Year 2 than in Year 1.

Conclusions: Penning gopher tortoises prior to release provides an important means of increasing site-fidelity in translocated gopher tortoises. The duration of penning is also important: individuals penned for one year were more site faithful and roamed over a considerably smaller area than those penned for nine months. After a year, the degree of dispersal of translocated individuals was similar to that reported in naturally occurring populations. In this instance, penning was an effective release technique and has potential application to other tortoise species.


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