Adult male gopher tortoise
Photograph by Michael J. Connor
Introduction
The gopher tortoise (Gopherus polyphemus) saga begins with the evolution of sandhill ecosystems originating from marine sand deposits in the Plio-Pleistocene geological period from 5 to 15 million years ago. These coastal sands eventually mixed with soils to provide the growing base for arid-type plants that preferred sandy, well-drained soils. The primary plant community is composed of longleaf pine, turkey oaks, and wire grass. These plants are fire resistant, and in fact, the entire community is called a fire subclimax forest. Natural and man-induced burning on a regular cycle is essential to maintain the character of this habitat. Other prominent plants include lichens, yuccas, palmetto, shrubs, wildflowers, gopher apple and prickly pear cactus.
Perhaps the most important animal in this ecosystem is the gopher tortoise. Its presence is apparent from the burrows which it digs into sandy soils. Its burrow may be 10 feet deep and 25-35 feet (diagonally) long, providing a well insulated refuge for the tortoise as well as 358 other species including 301 invertebrates and 57 vertebrate species. The creation of the burrow refuge has acknowledged the gopher tortoise by ecologists as the keystone species for its habitat. Among the inquilines (co-inhabitants of the burrow) include the dung beetle which converts the dung into soil nutrients, the gopher frog which is found nowhere else but in burrows, various snakes such as the pine snake, coachwhip racer, red rat snake, gray rat snake, the eastern diamondback rattlesnake and the threatened Eastern indigo snake. Occupiers of abandoned burrows include the fox squirrel, opossum, raccoon, red and gray foxes, bobcats, armadillo and bobwhite quail. Based on this extensive inventory, the gopher tortoise deserves the title of keystone species.
Distribution
Gopher tortoises are found from southeastern South Carolina through southern Georgia and most of Florida (except the Everglades), westward through southern Alabama and Mississippi and the eastern "toe" of Louisiana. They also occur on coastal islands off Georgia and Florida. Most of its habitat is located on private lands with a very small percentage located on public, state, federal or military reserves.
Biology and Ecology
The best way to sex a gopher tortoise is to gently turn one on its back and inspect its plastron or ventral surface. For adults, if the plastron is flat, it is probably a female. A concave plastron indicates a male. Juveniles cannot be sexed except by an expert. The gopher tortoise exhibits deferred sexual maturity, low fecundity and a long life span. Adults require 16-21 years to mature and may live 40 years or longer. Mating occurs during April to June, with females digging their nest cavity in the mouth of the burrow only once per year. The extremely low reproductive rate is a major limiting factor. The mean clutch size is approximately 6 eggs. The incubation period varies latitudinally from about 80-110 days. Nests are very susceptible to predation.
Nest loss may reach 87% due to various predators including snakes and mammals. Based on burrow counts in northern Florida, it is estimated that from time of egg laying through the first year, the recruitment potential can be reduced by about 94%. Hatchlings will either dig their own miniature burrow or seek shelter opportunistically under sand, debris, or litter.
Gopher tortoise density and movements are affected by availability of forbs and grasses. Home range is inversely related to the amount of herbaceous grass cover. As the principal sandhill grazer, the gopher tortoise feeds primarily on grasses, succulent plants and legumes. Legumes appear to be particularly important in the diet of juveniles. The gopher tortoise serves as a seed dispersal agent for native grasses and returns leached nutrients to the surface during burrow construction.
Population Status
Formerly common, the gopher tortoise has now been extirpated from parts of its range and many remaining populations are declining. Habitat destruction, habitat degradation through fire exclusion, and human predation have reduced the original number of tortoises by an estimated 80% over the last 100 years. A particularly unethical practice of "gassing" tortoise burrows to remove rattlesnakes is still legally allowed in Georgia, taking an unknown toll of gopher tortoises and inquilines. This wanton practice can also lead to the destruction of the burrow and refuge for the inquilines. In South Carolina, disjunct populations (estimated 200-2,000 individuals) exist in three counties, primarily on private lands. In south Georgia, which possibly contains the largest populations next to Florida, the tortoise still occurs on sand ridges in at least 81 counties. Throughout the Georgia Coastal Plain, populations have been fragmented by urban and agricultural development and depleted by over-harvesting and habitat destruction. Vast tracts of gopher tortoise habitat are owned by politically powerful forest products industry and associated private pine plantation owners. In Florida, the gopher tortoise remains relatively widely distributed, occurring in all 67 counties (estimated population 1.2 million). However, on the average, 1,000 people take up residency in Florida weekly. Unregulated growth reigns supreme, particularly in the southern part of the state, which displaces gopher tortoises to peripheral habitat. Gopher tortoises are still common in northern and central parts of peninsular Florida, but peripheral populations in the west and south have disappeared or are declining rapidly. Urban displacement, phosphate mining, and citrus production have had an impact on populations in central Florida. Human predation has depleted populations in the Florida Panhandle, and west Florida tortoise hunters now travel to Georgia and other states to illegally collect specimens. Tortoises occur in at least 21 counties in southern Alabama. Populations in that state appear to be recovering from past exploitation, however, exclusion of fire from upland habitats and creating corridors for highways and gas pipelines remain a problem. Agricultural and forestry practices have had a severe impact on tortoise populations in their 14 county range in southern Mississippi. The largest remaining population occurs in the DeSoto National Forest where the U.S. Forest Service is making a conscientious effort to protect and manage the species. Gopher tortoises have apparently been a relictual species in Louisiana as in South Carolina. Pine plantations with emphasis on thickly planted stands of loblolly pine have contributed to the near extinction of tortoises in Louisiana (estimated native population of less than 100).
Threats to Survival
The most significant threat is loss of habitat to intensive land use, particularly housing projects, industrial centers, corporate agriculture and forestry, phosphate strip-mining and sand extraction. As stated earlier, most of the land is in private ownership, with only a small percentage in military, federal or state reserves.
Another factor of importance is the exclusion of fire from natural longleaf pine and scrub oak habitats, thanks to the "Smokey the Bear" syndrome. An open canopy and relatively litter-free ground are necessary for food production and nesting, and such conditions are favored by regular burning. Tortoise numbers may be reduced by as much as 60-80% when burning is excluded for 8 or more years. The use of heavy machinery to reduce logging debris in preparation for planting pine trees is detrimental to gopher tortoises. However, studies in southern Georgia and northern Florida demonstrated that gopher tortoises are able to dig out following chopping treatment on deep sandy soils.
Tortoise response to more intensive site preparation techniques may vary substantially. Increased urbanization in Florida (1,000 new residents per week) has focused attention on displacement of tortoises. Tortoise relocation is being advocated by developers and their environmental consultants, and by regional planning councils with little thought to such biological impacts as carrying capacity of relocation habitats, population disruptions, gene pool mixing and parasite and disease transmission. However, the practice of relocation and transplanting has been widely practiced by resource agencies for many years for restoration of species such as deer, bear, alligators, sea turtles, and also with fish species including those raised in hatcheries.
Given the low reproductive potential, this species is very susceptible to over-harvest. Exploited in Florida for over 4,000 years, the gopher tortoise was a major food source for many families during the Depression. Due to prohibition or regulation of harvest, diminished tortoise populations, and the increase of "posted" private lands, the practice of collecting gopher tortoises for consumption purposes has declined. Some progressive state agencies have initiated law enforcement efforts to reduce illegal take. However, illegal commercialization still occurs in some areas. Although a one-time harvest is not necessarily the "death knell" for a colony, intensive predation pressure sustained over a long period could have a serious impact on local populations. Gopher tortoises are often considered pests on livestock ranges, and local hunters are sometimes enlisted to remove them. Other threats include mortality on highways and the collection of tortoises for pets or racing purposes. Irresponsible people vacationing in the South continue to pick up tortoises and bring them home as pets. They end up escaping or are dumped, walking the streets of Atlanta, Georgia, Nashville, Tennessee, Little Rock, Arkansas or other unsuitable locations. Large-scale rattlesnake roundups and legalized "gassing" in Georgia, and the use of agricultural chemicals may also have deleterious effects on tortoise populations.
Conservation Measures Taken
Some state agencies are enforcing conservation law and controlling illegal harvest. Georgia and Alabama list the gopher tortoise respectively as a protected "nongame species" and a "game species with no open season." Mississippi and South Carolina designate it "endangered." Although Louisiana affords the species no protection status, the Department of Wildlife and Fisheries is establishing an experimental population of gopher tortoises from confiscated and donated specimens on one of its wildlife management areas for research purposes and possible future relocation. In Florida, the gopher tortoise is a "species of special concern" and tortoise harvest is prohibited. In all states except Georgia, the U.S. Fish and Wildlife Service and the U.S. Forest Service prohibit the introduction of gasoline or other toxic substances into the gopher burrow.
The U.S. Fish and Wildlife Service listed the gopher tortoise as a threatened species in Louisiana, Mississippi and western Alabama during 1987. In 1990 the Service has distributed a draft recovery plan for the western population for public comment. The gopher tortoise is protected on all federal wildlife refuges, national parks and seashores, national forests and military reservations. The gopher tortoise is listed on Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Appendix II listing implies that commercial trade is allowed providing a permit from the country of export is obtained. This method provides for monitoring of international trade of all designated species.
Conservation Methods Proposed
Forest and range management that promotes grassy, open canopy habitat is necessary. Recommended management in natural longleaf pine-scrub oak stands include thinning of dense oaks, reestablishment of the pine component (to aid in carrying fire) and prescribed burning at least every 5-10 years where summer burns are feasible or every 2-4 years if winter burns are used. In commercial pine plantations using low intensity site preparation, planting fire tolerant species at wide spacings, maximizing edge, and burning annually or biennially will benefit tortoise populations. Other suggested conservation measures include establishment of refuges, protection from over-harvest, restocking in unoccupied habitats and public education. Captive propagation has been successful in many locations. Zoo Atlanta has been successful for several years in breeding its pair and rearing the juveniles. In some cases, juveniles have been returned to the wild. However, due to the recent discovery and outbreak of the respiratory disease syndrome in captive and wild tortoises, under no circumstances should tortoises be indiscriminately released without veterinary inspection and approval of the appropriate state or federal agency. Organized captive breeding programs are not required at this time.
Epitaph and Acknowledgments
Dr. Stephen R. Kellert, Professor at Yale University, School of Forestry and Environmental Studies reported in his 1979 study on Children's Attitudes, Knowledge, and Behavior Towards Animals, that the turtle ranked eighth among 33 other animals in an animal preference poll. It will take long-term dedicated effort from the public and conservation movement to insure the survival of all of our native turtles and tortoises. I acknowledge the Gopher Tortoise Council and Ms. Joan Diemer of the Florida Game and Fish Commission for their slides and narratives that is the substance of this presentation. Also, I thank Richard Martin of the Louisiana Department of Wildlife and Fisheries, Natural Heritage Program, for his slides. I have entered my own opinion and statements when appropriate.
References
Auffenberg, W. and Franz, R. 1982. The status and distribution of the gopher tortoise (Gopherus polyphemus). pp. 95-126. In: North American Tortoises: Conservation and Ecology. USDI, USFWS, Wildlife Research Report 12.
Diemer, J. 1986. The ecology and management of the gopher tortoise in the southeastern United States. Herpetologica 42(1):125-133.
Diemer, J. 1987. The status of the gopher tortoise in Florida. pp. 72-83. In: Proceedings of the Third Southeastern Nongame and Endangered Wildlife Symposium. Georgia Department of Natural Resources.
Diemer, J. 1989. Gopherus polyphemus, Gopher tortoise. pp. 14-16. In: The Conservation Biology of Tortoises. IUCN Species Survival Commission. Occasional Paper No. 5.
Kellert, S.R. 1979. Children's attitudes, knowledge, and behavior towards animals. Phase V Report on American Attitudes, Knowledge and Behavior Toward Wildlife and Natural Habitats. USDI, FWS, Washington, D.C. 20240.
U.S. Fish and Wildlife Service. 1987. Final rule: Threatened Status for the Gopher Tortoise. 50 CFR, 52(129).
U.S. Fish and Wildlife Service. 1990. Agency Draft: Gopher Tortoise Recovery Plan. 37 pages. USFWS, Endangered Species Program, Southeastern Regional Office, Atlanta, Georgia.
From: Proc. 1st Intern. Symposium on Turtles & Tortoises: Conservation & Captive Husbandry. Pages 77-79, 1991.
