The Effects of Translocation on Gopher Frog Survival and Behavior
Gopher frogs (Lithobates capito) frequently occupy gopher tortoise (Gopherus polyphemus) burrows and are considered gopher tortoise commensals. FWC policy previously allowed translocation of commensals along with gopher tortoises when they were removed from development sites, however concerns about impacts of translocations on commensal populations led to a temporary halt, pending further research.
This project was a pilot study to evaluate effects of translocation on gopher frog (Lithobates capito) survival and movement by experimentally translocating frogs (N = 23), then monitoring their movements with radio telemetry. Adult frogs were translocated from five different sites to a single recipient site (≥ 10 km apart), all in the Ocala National Forest in Marion County, Florida. As a comparison group, researchers used survival and movement data obtained from non-translocated frogs (N = 24) that were monitored in pre-translocation phases of this study and in a previous study. Fifty-nine percent of translocated frogs survived >30 days, compared to 77% of non-translocated frogs. However, longer-term survival was lower for non-translocated frogs, given five known mortalities and losses that occurred later in monitoring (at a mean of 85.6 d, SD = 57.1). Because higher rates of mortality than those observed are conceivable for amphibian translocations, researchers considered short-term success in this study to be moderately high. Furthermore, homing behavior was not observed among translocated frogs, and none were known to travel > 850 m away from the release site, suggesting reasonable potential for retention at the site. Nonetheless, substantial mortality occurred among translocated frogs, principally from predation during surface movements as they dispersed from the burrows where they were released.
The survival anlaysis showed a strong positive effect of daily probability of movement (DPM) on mortality for both translocated and non-translocated frogs. This indicates that movement and time spent at the surface is a strong driver of mortality risk, regardless of translocation status. After controlling for DPM there was no significant effect of translocation on mortality risk. Nonetheless, DPM was significantly higher for translocated versus non-translocated frogs. Thus, the primary factor affecting translocation success appears to be high post-release movement rates, leading to higher mortality rates.
Overall, the results suggest translocation may be a viable conservation approach when gopher frogs are at risk from habitat destruction at development sites. Although the results suggest high post-release mortality from predation, road mortality, or other causes following translocation, survival of translocated frogs is likely higher than that of frogs left in situ at development sites where all available habitat and breeding ponds will be destroyed. Nonetheless, further research is needed to assess longer-term survival and breeding, and to evaluate potential risks to recipient populations (e.g., disease transmission or negative genetic impacts). Additional research is also needed to determine whether interventions such as soft-release techniques might inhibit immediate dispersal and thereby improve survival for translocated frogs.