Line transect distance sampling and genetic analyses reveal a small but genetically diverse coastal gopher tortoise (Gopherus polyphemus) population

Gopher Tortoises inhabit coastal systems, including barrier islands, across the southeastern United States. St. Vincent National Wildlife Refuge is an uninhabited barrier island located off the coast of northwestern Florida. Although tortoises have been observed on the island, no information is available on the status of the population. We conducted a line transect distance sampling survey to evaluate the Gopher Tortoise population on St. Vincent Island. Additionally, we collected samples for genetic analyses from 11 individual tortoises captured opportunistically and via bucket traps on the island and 15 tortoises captured at nearby mainland sites. Surveys covered approximately 43% of the sampling frame and resulted in 55 burrows, 28 of which were occupied. The abundance estimate for the island was 52 tortoises (CI 95% 27–100) and the density was relatively low at 0.071 tortoises/ha (CI 95% 0.037–0.136). Genetic analyses of two mtDNA markers identified a new haplotype unique to St. Vincent Island and another 3 haplotypes previously found across the southeastern United States. The genetic composition of Gopher Tortoises on St. Vincent Island is representative of the entire southeast U.S. but most closely aligns with tortoise populations east of the Apalachicola-Chattahoochee River system. Although the tortoise population on this island is small, the extent of seemingly appropriate habitat on the island and the population’s genetic diversity suggests the potential for growth with added management intervention.