A multifaceted approach to evaluating gopher tortoise (Gopherus polyphemus) population health at selected sites in Georgia
Gonynor, Jessica Lynn
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Gopher tortoise (Gopherus polyphemus) populations are declining across the southeastern United States with an estimated decrease of >80% over the past 100 years. Declines have been attributed to habitat loss, overharvest, and disease. There is debate about the impact of the disease in free-ranging gopher tortoise populations. Cycles of convalescence and recrudescence of upper respiratory tract disease (URTD) have been confirmed in captive gopher tortoises, but to our knowledge, this has not been evaluated in free ranging populations despite URTD related die-offs in Florida. To date, despite extensive surveillance in tortoise populations for Mycoplasma, the causative agent of URTD, few evaluations of the survival of clinically ill tortoises have been conducted. Likewise, very little is known about parasites in Georgia tortoise populations. Through surveillance efforts of gopher tortoise populations we found that the prevalence of Mycoplasma agassizii and M. testudineum varied spatially, as did the diversity of endoparasites. We saw an all or none trend with exposure to M. agassizii. M. testudineum seroprevalence varied greatly among populations, ranging from 38% to 61%, with only one negative site. Clinical signs consistent with URTD were seen at sites seropositive for both pathogens. One site was selected to evaluate long term (15 year) impacts of URTD, including the recrudescence of clinical disease and its effects on tortoise behavior. Despite long-term exposure to the pathogen, tortoises in this population demonstrated site fidelity, stable home range size, and tortoise densities that increased through time. However we observed mortality and tortoises with severe clinical signs used significantly larger home ranges than asymptomatic tortoises within this population. These tortoises also made extremely long distance movements. Therefore, we feel that to examine the health of free ranging gopher tortoise populations, it is crucial to monitor the behavior of individuals with and without the disease, and consider other pathogens and parasites. We detected at least eight species of intestinal parasites in Georgia populations of gopher tortoises, including Cryptosporidium, a possible pathogen of tortoises. The primary goal of this dissertation was to assess gopher tortoise population health and behavior to provide information to aid in management of the species.