By Traci Castellón and Anna Deyle
The gopher frog (Lithobates capito) is native to the Southeastern U.S., where it primarily inhabits sandhill, flatwoods, scrub, and other upland habitats. The species is declining in many parts of its range and is currently being reviewed for federal listing under the Endangered Species Act.
The distribution of the gopher frog is closely associated with that of the gopher tortoise (Gopherus polyphemus), and it frequently lives commensally with tortoises in their burrows. Thus, gopher frogs are often encountered when burrows are excavated for gopher tortoise translocation. FWC policy previously allowed translocation of commensal species along with gopher tortoises. However, in 2012 concerns about potential impacts on commensal populations led to a halt in the practice pending research to assess outcomes.
Although translocation represents a potential strategy for mitigating impacts to animals that are at imminent risk due to habitat destruction, it also carries substantial risks. Few studies have assessed the impacts of translocation on amphibians, and translocation in adult gopher frogs has never been studied.
Translocation of amphibians is complicated because many species, including gopher frogs, have strong homing mechanisms that help them navigate to specific breeding ponds each year. This homing instinct is usually beneficial, but several translocations of amphibians have failed because animals tried to return to their capture site, often resulting in death as they attempted to navigate through an unfamiliar landscape.
To assess outcomes of gopher frog translocation, FWRI and HSC biologists are conducting a pilot study to experimentally translocate gopher frogs, then track them using radio-telemetry to evaluate survival and movement patterns. Gopher frogs were captured at breeding ponds and tortoise burrows from several locations in the Ocala National Forest and translocated to a single recipient site in another part of the forest.
Of the 21 translocated frogs, 67% survived for the duration of monitoring (2 to 5 months). Mortality was largely due to predation by snakes, which usually occurred within the first two weeks following translocation. Translocated frogs tended to have relatively high rates of movement immediately upon their release. During this period mortality was high, but survival increased once they settled into a single location (burrow or root hole) and began to move less frequently. None of the surviving frogs attempted a long-distance dispersal, either back toward the capture site or in any other direction, suggesting a relatively high probability for retention of translocated frogs at release sites. These preliminary results suggest that translocation may be a viable conservation approach when frogs are at risk due to habitat destruction at development sites.
In addition to our telemetry study, we plan to collect DNA samples from tadpoles at the recipient-site breeding pond for several years following the translocation. We will compare genetic samples from tadpoles with those from translocated adults to determine if any tadpoles captured at the recipient site are descended from translocated individuals. This would indicate that translocated frogs survived long enough to breed and were able to navigate to a breeding pond at the recipient site, both key indicators of translocation success.
Although translocation can be an effective tool for conservation under the right circumstances, it is not without risk. Future studies are needed to evaluate the risks of disease transmission, the impact of translocation on long-term survival and intra-specific competition, and to determine if movement and survival results from our pilot study hold true for populations in other locations. Nonetheless, our results suggest that gopher frog translocation has the potential for success, at least in terms of survivability and retention of translocated individuals at release sites.