The life history of four species in the Genus Graptemys are discussed in detail. In the last ten years, these species have taken on special significance because of their vulnerability and ecological importance.
Graptemys habitat in the southeast is characterized by clean, clear, limestone, spring-fed rivers and their tributaries. These rivers usually originate above the fall line and meander through the coastal plain to the Gulf of Mexico. Along the way they pass over expanses of flat, solution pocket limestone; carve out limestone bluffs; deposit sand in the form of beaches; and undercut banks toppling trees into the water creating snag areas.
Historically, these rivers were lined with cypress and tupelo trees which gave way in higher ground to hickory, oak, ash and pine. These bottomland, hardwood forests filter water, harbor a great diversity of plant and animal life and function as an integral part in the ecology of rivers. They in turn are fed with nutrients, when the river floods. As the South was settled, these rivers functioned as "highways" and settlements began to spring up along the banks. The bottomland-hardwood forests were a plentiful source of excellent timber and as a result were logged heavily during the 1900's.
Industrial sites in the South are almost exclusively close to a river to afford the industry with easy disposal of their waste products. Often these industries involve wood pulp production or chemical effluent being dumped directly into the river habitat.
In many localities, river habitat has been altered long before a local Graptemys sp. could be studied or even described. Thus, in many instances it is difficult to determine optimal habitat.
Another characteristic of rivers inhabited by Graptemys is that they are dynamic, with constantly shifting sands. This flow creates new beaches, converts old beaches to forest, changes the direction of the river channels, shapes oxbow lakes and ultimately shuffles optimal Graptemys habitat along the river course over a period of years. Dramatic evidence of this is demonstrated in the man-made structures such as docks seen stranded awash in silt or sand now far from the waters edge. Houses once believed to be a safe distance from the rivers are slowly undermined by collapsing banks. More permanent structures such as dams, levees or bulkheads interfere in this process and impede the river's ability to regenerate Graptemys habitat.
Consistent in all Graptemys observations regarding distribution within a river system is the fact that the species are not distributed evenly. Carr and Marchand (1942) first observed this during their historic canoe trip down the Chipola River in search of G. barbouri. "This trip demonstrates that the animals (G. barbouri) were not distributed evenly throughout the river, but were localized in areas in which the water was relatively deep (5-12 feet) and the bottom was made up of exposed shelving limestone with numerous pits and depressions. Over and on such bottom as many as thirty individuals were seen within a radius of a hundred yards, whereas two days' travel over gravelly, boulder strewn and silt covered bottom only yielded two specimens."
The above passage is very revealing in that it describes what was believed to be optimal habitat and density for G. barbouri in the Chipola River of Florida fifty years ago. Secondly, to date, the description stands as a model of optimal habitat not only for G. barbouri but also for G. caglei and other Gulf Graptemys occurring in limestone associated rivers.
Endemic to the Guadalupe River system of Texas, G. caglei is found in concentrations in similar limestone "riffle bar" habitat (Killebrew, pers. comm.). This "riffle bar" habitat is constantly being threatened by siltation, impoundment and other forms of habitat alteration (Price, pers. comm.).
A review of some of the literature describing optimal habitat for G. flavimaculata and G. oculifera in Mississippi are as follows:
G. flavimaculata - Location: Chickasawhay River
- Cagle, 1954--"River is 30-150 feet wide; the banks have exposed areas of limestone in many places and the bottom is generally rock and sand - abundant in the snags in the slower current."
- McCoy and Vogt, 1980--Viewed "critical habitat" for G. flavimaculata to be on the Pascagoula River from the town of Wade north into the Leaf River at the town of Merrill without describing the habitat. This area of the Pascagoula no longer supports the largest concentrations of G. flavimaculata and is characterized by alternating large, sand beaches and snag areas adjacent to undercut banks (Jones, pers. comm). The current here is moderate to fast depending on volume.
G. oculifera - Location: Pearl River
- Cagle, 1953--"Wide sand beaches, a narrow channel and fast current."
- McCoy and Vogt, 1980--"Fast to moderate current where basking logs are numerous, the river wide enough to allow sun penetrations to basking logs from 1000-1600 hours, and large high sand and gravel bars adjacent to the river readily available for nesting."
- Stewart, 1988--"Moderate current, numerous basking logs and sun penetrating for several hours."
Observation of Graptemys nesting and nest site locations vary greatly in the literature. The relationship between Graptemys nest sites and survivorship of eggs and hatchlings has not been explored. The critical factors in hatching success are temperature, moisture level and substrate particle size. These factors can be met in a wide variety of nest-site localities as observed by many authors. McGehee (1990) concluded that moisture content directly affected hatchling size and survival during the incubation of Caretta eggs. Shealy (1976) reported factors influencing G. pulchra nesting in decreasing importance were - sand particle size, elevation above the water level, cover quality and distance from waters edge. Lahonas (1981) found that optimal nest sites for the G. nigrinoda delticola were located in open expanses of fine sand on a large, sand beach situated on the north side of Gravine Island, Tensaw River, Baldwin County, Alabama. This beach is the only significant "beach" along the Tensaw River and was created from sand dredged from the river channel approximately 50 years ago. The author has found that G. nigrinoda delticola occurring upstream in heavily forested riparian habitat near Stockton, Alabama, will nest in sandy loam within a meter of the river. Plundered, empty nests in the same location believed to be G. nigrinoda delticola are scattered along wooded banks between cypress trees or on access roads to the river. It appears that Graptemys will nest in sandy, well-drained soil associated with available vegetation, on steep banks or along the back of sand bars large or small.
Predation of recently deposited Graptemys eggs by the fishing crow, raccoons and other mammalian predators is a major factor limiting Graptemys populations. The impact of fire ants on eggs or emerging hatchlings has been observed but not measured. Once hatchlings emerge, they may fall prey to birds, predatory fish, alligators and alligator snapping turtles. Adult female Graptemys are vulnerable to predation during the nesting sequence as evidenced by the occasional carcass found gutted along the river banks or nesting beaches.
The greatest threat to Graptemys populations is the rapid degradation and alteration of habitat in and adjacent to the rivers of the southeastern United States. The nature of river habitat, being continuous from its source to the Gulf of Mexico, may help to jeopardize Graptemys. Populations in the lower drainage can may be adversely affected by degraded water quality despite the presence of suitable habitat.
The significance and vulnerability of the above mentioned Graptemys species cannot be emphasized enough. Dams for energy production and flood control have altered riverine habitat substantially. Agriculture and industry along the banks or tributaries has contributed greatly to the siltation of the rivers, choking the life from aquatic flora and fauna which constitute Graptemys food items. Silt or mud deposits on nesting sites may limit hatching success. Paper mills and other industries dumping toxic effluent into Graptemys habitat along with sewage and storm drain run-off from rapidly growing population centers, takes its toll on water quality with unknown consequences to Graptemys populations. Increased recreational use of the rivers and nesting beaches by boaters, ATVs and campers may also impact nest site selection, incubation or hatching success. Specimens taken by private, institutional or commercial collectors, turtles shot from basking sites for "sport" and those harvested for food also impact the populations.
Conservation measures taken to protect Graptemys populations and habitat have been on the increase in recent years. In Florida, G. barbouri is protected and possession of the species is limited to two individuals with aims at discouraging commercial collection for the pet trade or for human consumption. Graptemys conservation efforts are the greatest in Mississippi, with G. oculifera and G. flavimaculata both afforded protection on the state and federal level. The Pascagoula River Wildlife Management Area, composed of 37,000 acres of state protected land on both sides of the lower Pascagoula, no doubt will be instrumental in the future of G. flavimaculata. Water quality in the Pascagoula is the primary concern for the survival of this Graptemys (Jones, pers. comm.). A portion of this is G. oculifera habitat along the Pearl River, above Ross Barnett Reservoir, has been designated as a Ringed Sawback Sanctuary, the first Graptemys sanctuary and hopefully a model for future preserves. In addition to efforts to protect more river habitat, Mississippi has gated access roads and posted signage prohibiting vehicles from potential Graptemys nesting areas. A policy adopted in some areas of the Pearl River is to move deadfall trees or snags out of the central river channel towards the banks to accommodate boat or water skier traffic. This, opposed to the removal of the snags, insures the presence of suitable basking sites and feeding areas for Graptemys. Hopefully, these efforts will prove to be beneficial to both Graptemys and those using the rivers for recreational activity and will be adopted by other state agencies.
We can all do our part in insuring that Graptemys have a future in the wild by supporting primary research in the field and observing conservation guidelines for both habitat and Graptemys. Those of us with Graptemys in private or public collections should manage our captives responsibly by pursuing breeding programs and educating others in the role that Graptemys assume in river ecology and their association with other turtle species composing some of the most valuable and diverse turtle habitat in the world.