Management of Gopher Tortoise (Gopherus polyphemus) Using Coastal Habitats Active
USGS researchers will conduct research on St. Vincent National Wildlife Refuge and throughout coastal habitat in Northwest Florida to inform future management decisions in the Refuge and contribute to the growing knowledge of the ecology of gopher tortoises using coastal habitats.
The Science Issue and Relevance: The gopher tortoise (Gopherus polyphemus) was federally listed as Threatened in 1987 in the portion of their range west of the Mobile and Tombigbee Rivers in Alabama. The gopher tortoise is one of the most highly studied vertebrate species in the southeastern U.S. (Gaillard et al. 2017, Menges et al. 2017, Stober et al. 2017). However, management needs have not been examined for tortoise populations using coastal habitats, particularly on barrier islands. A range-wide genetic study investigating population structure of gopher tortoise in the southeastern U.S. included samples from only three coastal sites across the entire region (Gaillard et al. 2017). In southwest Florida, tortoises from Marco Island were genetically distinct from those found on the associated mainland (Gaillard et al. 2017, Winters et al. 2017). Those findings suggested insular tortoise populations may require separate management considerations from mainland populations including decisions about translocation of tortoises for population recovery purposes. Although gopher tortoises have been reported using barrier islands throughout the northern Gulf of Mexico, no samples were included from those areas and few studies have been conducted in that region.
Methodology for Addressing the Issue: To determine the size of the population, a line transect distance sampling survey is being performed. This is a standard methodology to acquire an accurate estimate of adult and sub-adult tortoises in a specific area. This survey will be repeated in future years to determine whether the population is growing, shrinking, or remaining stable.
To understand the demographics and genetics of the population, tortoises will be captured, tagged, measured, and sampled. Tortoises will be marked for future identification using a Passive Integrated Transponder (PIT) tag and marginal scute notches. The biological sample will be used in genetic analyses. A subset of captured tortoises will be tracked with very high frequency (VHF) technology and novel, very small, low-cost, and power efficient Global Navigation Satellite System (GNSS) tags to identify the habitat use and home range.
Future Steps: This work will inform future management decisions in St. Vincent National Wildlife Refuge (NWR) and contribute to the growing knowledge of the ecology of gopher tortoises using coastal habitats. For example, the primary reason to conduct prescribed burns on the Refuge is to improve habitat for tortoises, yet the lack of knowledge about tortoise distribution hampers those decisions. Information gathered during this study could also benefit other coastal refuges such as St. Marks NWR, Bon Secour NWR, and Lower Suwannee NWR.
In addition, this project will contribute to a larger study of coastal tortoise populations that we are conducting across Northwest Florida including within the Apalachicola National Estuarine Research Reserve, on Tyndall Air Force Base (AFB), and on Cape San Blas. One of the primary threats to tortoises mentioned in the U.S. Fish and Wildlife Service’s Petition to List is “insufficient fire management”. In addition, habitat fragmentation, destruction, and modification from human development is considered one of the most significant threats. St. Vincent NWR is an undeveloped, protected habitat that could serve as a refuge for tortoises from human development. Understanding population structure, recruitment, and abundance of tortoises in this coastal refuge would directly address those issues. This study would also serve as a template for other coastal refuges and federally managed lands, such as Tyndall and Eglin AFBs and Gulf Islands National Seashore.
USGS researchers will conduct research on St. Vincent National Wildlife Refuge and throughout coastal habitat in Northwest Florida to inform future management decisions in the Refuge and contribute to the growing knowledge of the ecology of gopher tortoises using coastal habitats.
The Science Issue and Relevance: The gopher tortoise (Gopherus polyphemus) was federally listed as Threatened in 1987 in the portion of their range west of the Mobile and Tombigbee Rivers in Alabama. The gopher tortoise is one of the most highly studied vertebrate species in the southeastern U.S. (Gaillard et al. 2017, Menges et al. 2017, Stober et al. 2017). However, management needs have not been examined for tortoise populations using coastal habitats, particularly on barrier islands. A range-wide genetic study investigating population structure of gopher tortoise in the southeastern U.S. included samples from only three coastal sites across the entire region (Gaillard et al. 2017). In southwest Florida, tortoises from Marco Island were genetically distinct from those found on the associated mainland (Gaillard et al. 2017, Winters et al. 2017). Those findings suggested insular tortoise populations may require separate management considerations from mainland populations including decisions about translocation of tortoises for population recovery purposes. Although gopher tortoises have been reported using barrier islands throughout the northern Gulf of Mexico, no samples were included from those areas and few studies have been conducted in that region.
Methodology for Addressing the Issue: To determine the size of the population, a line transect distance sampling survey is being performed. This is a standard methodology to acquire an accurate estimate of adult and sub-adult tortoises in a specific area. This survey will be repeated in future years to determine whether the population is growing, shrinking, or remaining stable.
To understand the demographics and genetics of the population, tortoises will be captured, tagged, measured, and sampled. Tortoises will be marked for future identification using a Passive Integrated Transponder (PIT) tag and marginal scute notches. The biological sample will be used in genetic analyses. A subset of captured tortoises will be tracked with very high frequency (VHF) technology and novel, very small, low-cost, and power efficient Global Navigation Satellite System (GNSS) tags to identify the habitat use and home range.
Future Steps: This work will inform future management decisions in St. Vincent National Wildlife Refuge (NWR) and contribute to the growing knowledge of the ecology of gopher tortoises using coastal habitats. For example, the primary reason to conduct prescribed burns on the Refuge is to improve habitat for tortoises, yet the lack of knowledge about tortoise distribution hampers those decisions. Information gathered during this study could also benefit other coastal refuges such as St. Marks NWR, Bon Secour NWR, and Lower Suwannee NWR.
In addition, this project will contribute to a larger study of coastal tortoise populations that we are conducting across Northwest Florida including within the Apalachicola National Estuarine Research Reserve, on Tyndall Air Force Base (AFB), and on Cape San Blas. One of the primary threats to tortoises mentioned in the U.S. Fish and Wildlife Service’s Petition to List is “insufficient fire management”. In addition, habitat fragmentation, destruction, and modification from human development is considered one of the most significant threats. St. Vincent NWR is an undeveloped, protected habitat that could serve as a refuge for tortoises from human development. Understanding population structure, recruitment, and abundance of tortoises in this coastal refuge would directly address those issues. This study would also serve as a template for other coastal refuges and federally managed lands, such as Tyndall and Eglin AFBs and Gulf Islands National Seashore.