Evaluating the utility of translocation for turtle conservation
Tuberville, Tracey D.
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Two-thirds of the world’s turtle species are considered threatened. As exploitation and habitat alteration continue to cause population declines and extirpations, translocations play an increasingly important role in turtle conservation. However, few translocation efforts have been thoroughly evaluated to determine their success. I present a framework for evaluating translocation success, using the gopher tortoise (Gopherus polyphemus) as a case study. This framework includes monitoring three processes that influence population stability - emigration, survivorship and reproduction. Experimental releases and two years of subsequent monitoring via radiotelemetry were conducted on the Savannah River Site, SC, to test the relative effectiveness of no penning, 9-month and 12-month penning treatments. Penning significantly increased site fidelity both in terms of reducing activity areas and reducing the proportion of animals dispersing. Long-term survivorship was investigated in a population of gopher tortoises established through multiple releases on St. Catherines Island (SCI), GA. Based on 12 years of mark-recapture data analyzed in program MARK, apparent survival of newly released tortoises was temporarily reduced, most likely as a result of permanent dispersal of some tortoises from the release area. However, apparent survival of translocated tortoises was consistently high once they became established as residents. Mating system was also investigated in the SCI translocated population by genetic sampling of 27 adult males, 34 adult females, and 121 offspring collected from 19 clutches. Paternity (and maternity, if not already known) was assigned based on genotypes at five microsatellite loci. Reproductive success varied among males, with larger males siring more offspring. Among successful sires, previously established resident males sired a disproportionate number of the offspring sampled, despite being significantly smaller than subsequently released males. Finally, population models based on current literature suggest that gopher tortoise populations are either declining or the species’ life history is inadequately characterized. Simulation of different translocation scenarios indicate that translocation can be used to establish viable populations but that release protocols can have important long-term demographic consequences. These studies demonstrate that translocation can be a useful tool for managing gopher tortoise populations and also provide a comprehensive framework for evaluating translocation success in other species.