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Macrochelys suwanniensis Thomas, Granatosky, Bourque, Krysko, Moler, Gamble, Suarez, Leone, Enge and Roman, 2014
Suwannee Alligator Snapping Turtle
Federal Protection: Listed Threatened
State Protection: Threatened
Global Rank: G2
State Rank: S2
Element Locations Tracked in Biotics: Yes
SWAP 2015 Species of Greatest Conservation Need (SGCN): No
SWAP 2025 Species of Greatest Conservation Need (SGCN): Yes
2025 SGCN Priority Tier: Highest Conservation Concern
Element Occurrences (EOs) in Georgia: 26
Habitat Summary for element in Georgia: Large blackwater rivers and streams in reaches with woody debris, deep pools and undercut banks
The Suwannee alligator snapping turtle was first described as a species separate from the western alligator snapping turtle (Macrochelys temminckii) in 2014. Currently, the largest documented alligator snapping turtle is a Macrochelys suwanniensis specimen (80.1 cm or ~31 inches maximum carapace length) making the Suwannee alligator snapping turtle (usually 30-50 cm or 12-30 inches carapace length in adults) the largest freshwater turtle species occurring in North America and arguably the fourth largest in the world, surpassed only by the Yangtze giant softshell turtle (Rafetus swinhoei) (100 cm or ~39 inches) of Asia, the Nile softshell turtle (Trionyx triunguis) (94 cm or 37 inches) of Africa, and the giant South American river turtle (Podocnemis expansa) (90 cm or ~35 inches). The generic name for the alligator snapping turtles is fitting, since Macrochelys means “large turtle.” As is the case for all chelydrid turtles (snapping turtles), this species has a total of 25 marginal scutes (including the cervical scute) on the perimeter of the carapace (upper shell). Both species of alligator snapping turtles have a row of three (occasionally more) supramarginal scutes situated between marginal scutes and the first three lateral scutes on each side of the carapace (Figure 1.). The carapace is large, rough, dark-brown, dark-gray, or sometimes yellowish, and strongly serrated posteriorly. There are three prominent keels running longitudinally along the length of the carapace, one down the center along the vertebral scutes, and a keel down each side of the carapace along the lateral scutes; there are knobs along these keels on each vertebral & lateral scute that are curved anteriorly. The largely reduced plastron (lower shell) is yellowish in color and characterized by off-set abdominal or “preabdominal” scutes (Figure 1.). The skin is dark brown to gray, but lighter below. The head is covered in elaborate papillae (small pimple-like fleshy projections) and the eye is ringed with conical tubercles (bumps of skin), all of which produce the effect of expertly camouflaging the turtle’s head with vegetation and woody debris typical of the species’ habitat. The upper jaw is strongly hooked. Hatchlings (3-4.5 cm or 1.25 - 1.75 inches carapace length) that look much like adults, have roughened carapaces, long, slender tails, and dark brown skin (sometimes possessing lighter mottling).
Among Georgia’s native turtle species, only the common snapping turtle (Chelydra serpentina) (within the same family, Chelydridae) could be confused with an alligator snapping turtle (genus Macrochelys); but common snapping turtles can be differentiated by the following: 1) both eyes are clearly visual from above; 2) dorsal projections along the tail are prominent relative to species of Macroclemys; and 3) possesses a carapace a) without supramarginal scutes, b) lacking prominent knobs on the vertebral or lateral scutes, and c) lacking keels at all or at least that extend the entire length of the shell (Figure 2).
The Suwannee alligator snapping turtle can be differentiated from the western alligator snapping turtle (Macrochelys temminckii) by the respective species’ allopatric (non-overlapping) geographic distribution and through the comparison of shell characteristics, namely the 1) width and general shape of the caudal notch; and 2) the position of the “preabdominal” scute. Within Georgia, the western alligator snapping turtle occupies the lower Chattahoochee, Flint, and Ochlockonee rivers and their tributaries; the Suwannee alligator snapping turtle occupies the Suwannee River watershed. Among adult alligator snapping turtles, species can be physically differentiated by the comparison of the relative distance between distal tips of right and left 12th marginal scutes (x) to distance between distal tips of 11th and 12th marginal scutes (y) (Figure 3. E. & F.). If x > y, then the turtle is a Suwannee alligator snapping turtle. Since carapace morphology cannot be used to definitively determine a species identification for hatchling and juvenile alligator snapping turtles, and because the suture between the pygal and peripheral bones are discernible in radiographs (x-rays), if the geographic origin of a turtle is unknown, an x-ray of the posterior carapace may be necessary to determine the relative position of the pygal bone to the supracaudal scutes (scutes immediately adjacent and above the tail) and marginal scute cusps; for M. suwanniensis the pygal bone is completely contained within the caudal notch (Figure 3. A., B., C., & D.). Additionally, on the plastron, the “preabdominal” scute is laterally off-set relative to the abdominal scute in M. suwanniensis, but anteriorly off-set to the abdominal scute in M. temminckii (Figure 1.).
Preferred habitats of M. suwanniensis typically consist of lotic (flowing), deeper waters of large rivers and major tributaries (especially spring-fed portions), but this species are also found in lentic (still water) canals, impounded ponds & lakes (particularly of larger rivers), oxbows, swamps, including turbid and tannin-stained backwaters of swamp forest floodplains. Aquatic microhabitats important for alligator snapping turtles include under-cut banks, limestone ledges, scour holes, large woody debris, essential habitat features serving as both refugia and as substrate necessary for ambushing prey.
Unlike Coastal Plain rivers that originate as alluvial systems within the Piedmont, all of the rivers (and their tributaries) of the Suwannee River watershed originate within the Coastal Plain, which characterizes them as “blackwater.” Blackwater rivers are so named because their deep water appears black in color, however the shallows of the stream edge appear reddish or tea-colored – the color derived from organic acids leached from swamps on tributary floodplains. Unless influenced by the upwelling of groundwater within spring-fed stretches, waters of these rivers are tannin-stained. Unlike alluvial rivers of the Piedmont characterized by possessing relatively wide floodplains (with extensive tracts of bottomland hardwoods), blackwater streams lack a prominent floodplain. Consequently, the Little, Withlacoochee, and Alapaha rivers inundate their narrow floodplains for long periods of time, which are mostly occupied by very wet gum-cypress communities. However, the stage of these rivers fluctuates widely, often exposing formerly submerged logs and sandbars in the autumn; this variation in river stage confines alligator snapping turtles to the larger, by relatively narrow rivers and streams. While much of these blackwater streams flow over glaringly white sands, some portions of these rivers flow over shallow limestone shoals (i.e., the Alapaha & Suwannee rivers) or their flow becomes subterranean within limestone strata south of Valdosta (i.e., the Alapaha River).
Though alligator snapping turtles are omnivores and individuals likely feed on any animal that they can capture, subdue, and shallow, the majority of their diet consists of fish. Macrochelys are particularly adapted to ambush fish; the inside of their months is camouflaged to blend into the surrounding when open underwater and they possess a double-ended moveable worm-shaped appendage attached to the anterior third of the oral cavity, anterior of the glottis – an example of aggressive mimicry, as it has specifically evolved as a lure for fish. Other documented food items include plant fruits and parts (e.g., briar roots, wild grapes, hickory nuts, locust beans, oak acorns, palmetto fruits, persimmons, tupelo fruits), leaches, freshwater clams, mussels, and snails, crayfish, large salamanders, turtles, snakes, small alligators, birds, and small mammals. Some larger prey animals have been known to be taken by alligator snapping turtles as carrion.
Macrochelys are the only turtles in the world with an oral predatory lure (resembling a worm or insect larva), which both adults and juveniles use to lure prey into biting range; this “worm” appendage is white or pale pink (juveniles) or mottled or smoky gray (adults) while at rest, but becomes suffused with red when active, contrasting with the gray-black of the oral cavity.
The only time alligator snapping turtles ever leave the water, is when females dig nests within sandy soil 8-656 feet (2.5-200 m) from the nearest water and less than 10 feet (~3 m) above it, avoiding open sandbars and low forested areas with leaf litter and matted roots. Nesting for M. suwanniensis begins in April and early May. Hatching occur 80-115 days after oviposition, depending on ambient temperature. Sex of individual alligator snapping turtles is determined by the temperature at which the egg incubates during embryonic development while in the nest; 11% males at 72.5°F (22.5°C), 69% males at 77°F (25°C), and 71% at 80.6°F (27°C), no males at 86°F (30°C) (i.e., temperature sex determination pattern TSD – 2).
Perhaps as an adaptation to its typically deeper, swift water, the tails of small alligator snapping turtles are reportedly prehensile habitats (i.e., can maintain a position in a current by hooking their tails around fixed objects). As individuals are rarely seen basking, research suggests that alligator snapping turtles thermoregulate by altering their depth in the water column, however Macrochelys turtles cannot remain submerged as long as many other turtles (i.e., must surface after 15-20 minutes in warm water).
Snorkeling or SCUBA diving in clear water may be conducted to visually locate individuals, but deployment of large, heavy-duty hoop traps, particularly in blackwater systems with low visibility, are a more effective survey method. Trapping is ideally conducted March through November, when alligator snapping turtles are most active (individuals no longer forage for prey when the ambient air temperature falls below 18°C (65°F). Baited hoop traps should be set within and upstream of suitable habitat (i.e., adjacent to preferred microhabitats and within discernible to moderately flowing current). Within previous survey efforts, researchers have successfully used single-funnel hoop traps of various sizes, depending on field situations such as different water depths. Hoop traps should be positioned so that a funnel entrance is facing downstream, and so that the longitudinal axis of the hoop trap is approximately parallel to the stream flow with the current flowing through the throat of the trap, and should be baited with cut fish contained within a partially open vessel which is secured inside the back of the trap’s funnel throat and suspended into the approximate center of the trap diameter. At least the upstream and second trap hoops should be secured to the stream substrate (or large woody debris); if suitable rocks, limbs or root systems are unavailable for securing traps, staking may be required to secure the trap. To allow trapped animals, including alligator snapping turtles, to surface and avoid drowning, hoop traps should be positioned and secured so as to allow a portion of the upper part of the trap to be emergent from the water surface. Consideration should be given to the timing and feasibility of placement of traps on stream and river segments that could possibly experience rising flood water conditions, as stormwater flows could overtop set hoop traps, creating a drowning hazard for captured animals. Conversely, setting traps amid reduced stream discharge due to seasonality or drought could create a lack of flow rendering otherwise suitable habitats suboptimal, encouraging turtles to move to more stable habitats, limiting the success of trapping efforts. To maximize trapping results, hoop traps should remain in place for at least 12 to 20 hours, though they may be checked for captures as frequently as every hour or two, but no less frequently than every 24 hours so that captured animals can be removed, and to avoid escapes and drownings (previous research has shown that the majority of alligator snapping turtle individuals are captured within the first 24 hours of a trap set). Use of such turtle traps are only legal in Georgia by issuance of a permit by the Georgia Department of Natural Resources.
Unlike the wider-ranging western alligator snapping turtle, the Suwannee alligator snapping turtle is endemic to the Suwannee River watershed of Florida and Georgia. In Georgia, M. suwanniensis is currently distributed widely throughout southcentral Georgia in medium- to large-sized streams within the Suwannee River drainage, however the relative abundance of this turtle within tributary streams is apparently lower in Georgia than in Florida. Historically, in Georgia, M. suwanniensis was considered abundant within the Suwannee River and its larger tributaries, Jones, Suwannoochee, Cypress, and Tom’s creeks; the Alapaha River and its larger tributaries, the Alapahoochee and Willacoochee rivers; the Withlacoochee River and its larger tributaries, the New and Little rivers and Okapilco, Piscola, and Warrior creeks; as well as the St. Mary’s River (Atlantic slope) drainage of the Okefenokee Swamp (but has never been documented from the main stem of this river outside of the swamp). Survey efforts over the past 25 years have documented occupancy of this species within all of the aforementioned streams except Cypress Creek, but see the “Conservation Status” section below.
Although alligator snapping turtle longevity is at least 80 years (likely much longer) and research has shown adult annual survivorship is 99%, the typical pattern characterizing all turtle species – delayed sexual maturity (11-13 years), low fecundity (clutch size, 15-50, annually) and low nest and yearling survivorship (clutch success is variable, but juvenile survivorship is 32%), make them vulnerable to over harvest or mortality, especially of sexually mature females.
Within Georgia, sport trotlines, set hooks, bush hooks, limb lines, and jug lines that are deployed recreationally to fish for catfish are often deployed without labeling, without restriction as to quantity, and are also easily abandoned without recourse. Field observations suggest that both attended, and especially abandoned trotlines, set hooks, bush hooks, limb lines, and jug lines pose a problem for Macrochelys bycatch and mortality through ensnarement and hook ingestion. Recent research has shown that the incidence of bycatch of Macrochelys involving fishhooks to be four times more numerous than the second-most numerous threat, turtle persecution (i.e., wanton killing).
The magnitude of the effects of habitat alteration resulting from the removal of large woody debris (e.g., “deadhead logging”) is largely unknown, but is likely significant.
| Threat 1 | Threat 2 | Threat 3 | |
|---|---|---|---|
| General Threat | Human intrusions & disturbance | Biological resource use | Biological resource use |
| Specific Threat | Recreational activities | Fishing & harvesting aquatic resources | Logging & wood harvesting |
The state of Georgia prohibited the take (including commercial harvest) of alligator snapping turtles and their eggs by designating Macrochelys as State Threatened under Georgia's Endangered Wildlife Act in 1992, but this did not prohibit the use of freshwater turtle traps for other turtles species during which Macrochelys could be bycatch. However, Georgia’s freshwater turtle regulations (Chapter 391-4-16) enacted in 2012 and revised in 2018 made it illegal to deploy turtle traps within Georgia’s public or private waters without a permit issued by the Georgia DNR (i.e., permitted nuisance wildlife control operator or a commercial fishing permit issued in conjunction with a commercial turtle-farming permit). In 2006, Macrochelys was listed as Appendix III under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), and as an Appendix II species in 2023. Following the development of a Species Status Assessment, the US Fish and Wildlife Service listed Macrochelys suwanniensis as Threatened under the U.S. Endangered Species Act in 2024.
Lower relative abundance of M. suwanniensis within Georgia relative to Florida may be indicative of past intensive harvest and slow population recovery. Despite the species’ legal protection today, intensive commercial trapping that occurred in the late 1960s and early 1970s meant that the Little and Withlacoochee rivers in Georgia were “trapped out” by 1982; fortunately, recent surveys have shown that populations within these rivers have at least partially recovered following legal protection of the species. Researchers’ inability to capture M. suwanniensis within the upper Suwannee River main stem (from the entrance to Stephen C. Foster State Park, Georgia to White Springs, Florida) may reflect the intense trapping pressure on the species until approximately 1973 along this river stretch and suggests the populations likely have not recovered from past over-harvest; it is also possible that M. suwanniensis was naturally low in abundance within the upper Suwannee River main stem through influence of the Okefenokee Swamp outflow chemistry (low nutrients, low pH, and potentially related low prey availability). Although described as “being frequently hooked” within the Suwannee Canal in the 1930s, there have been only four verified occurrences of M. suwanniensis within the Okefenokee Swamp. Following extensive wildfires in the mid-1950s, the headwaters of the Suwannee River were impounded in 1960-1962 (i.e., the Suwannee River Sill) raising the maximum water level of the swamp by 12 cm (~4.75 inches), the influence of which extends 60 km (~37 miles) into the swamp; the effect of this hydrologic change (i.e., from a naturally dynamic riparian [river-like] environment to a palustrine [lake-like] environment) on M. suwanniensis is unknown. However, elsewhere within the species’ range in Georgia, riparian habitats remain predominantly intact. For instance, numerous deep, natural swamp lakes are distributed along the channel of the Alapha River, providing prime habitat for the Suwannee alligator snapping turtle, which has been documented from the swamp lakes of the Alapaha Wildlife Management Area.
The long-term survey and monitoring of select Georgia populations (using mark-recapture methods) should be continued (periodically monitored) in order to establish baseline demographics and to identify possible future population declines. The impacts of legal fishing methods (e.g., trotlines, bush hooks, limblines, etc.) on turtle bycatch and mortality should be evaluated and means of mitigation of these risks explored. Because underwater snags, logs, and limbs (i.e., large woody debris) provide the habitat for the larval insects that are the foundation of vertebrate food webs within these otherwise nutrient deficient (i.e., blackwater) streams, the need to regulate wood removal (i.e., “deadhead logging”) should be assessed. Impacts to riparian habitats from upland land use should be minimized; forestry best management practices including the implementation of stream management zones within the turtle’s range should be implemented during forestry operations in order to minimize erosion of the uplands and sedimentation input into adjacent stream channels.
Enge, K. M., D. J. Stevenson, T. M. Thomas, G. R. Johnston, J. B. Jensen, B. S. Stegenga, H. C. Chandler, and P. E. Moler. 2021. Distribution and relative abundance of the Suwannee alligator snapping turtle (Macrochelys suwanniensis). Chelonian Conservation and Biology 20(2): 184-199.
Folt, B. and C. Guyer. 2015. Evaluating recent taxonomic changes for alligator snapping turtles (Testudines: Chelydridae). Zootaxa 3947(3): 447-450.
Jensen, J. B. and W. S. Birkhead. 2003. Distribution and status of the alligator snapping turtle (Macrochelys temminckii) in Georgia. Southeastern Naturalist 2(1): 25–34.
Johnston, G. R., J. S. Geiger, T. M. Thomas, K. M. Enge, E. Suarez, and B. Davis. 2023. Maximum body size of the Suwannee alligator snapping turtle (Macrochelys suwanniensis). Southeastern Naturalist 22(sp12): 418-428.
Johnston, G. R., T.M. Thomas, E. Suarez, A. Lau, and J. C. Mitchell. 2015. Population structure and body size of the Suwannee Alligator Snapping Turtle (Macrochelys suwanniensis) in northern Florida. Chelonian Conservation and Biology 14(1): 73-81.
Stegenga, B. S., D. J. Stevenson, and H. C. Chandler. 2023. Observations of the Suwannee alligator snapping turtle from the Okefenokee Swamp. Southeastern Naturalist 22(sp12): 78-83.
Stevenson, D. J., B. S. Stegenga, B. Rice, J. Barrett, J. Bolton, Z. Cava, H. C. Chandler, K. M. Stohlgren, T. Brock, C. D. Camp, J. B. Jensen, M. D. Moore, S. McGuire, C. Howe, F. H. Snow, J. Oguni, C. Coppola, and L. L. Smith. 2021. New county records for amphibians and reptiles in Georgia. Herpetological Review 52(2): 350–359.
Thomas, T. M., K. M. Enge, E. Suarez, P. Schueller, B. Bankovich, and E. H. Leone. 2023. Home range and habitat selection of the Suwannee alligator snapping turtle (Macrochelys suwanniensis) in the Suwannee River, Florida. Chelonian Conservation and Biology 22(2): 146-155.
Thomas, T. M., K. M. Enge, E. Suarez, S. C. Barry, and S. A. Johnson. 2023. Variation in relative abundance, population structure, and body size of the Suwannee alligator snapping Turtle (Macrochelys suwanniensis) in the Suwannee River. Southeastern Naturalist 22(sp12): 264-274.
Thomas, T. M., K. M. Enge, E. Suarez, and G. R. Johnston. 2022. Population status of the Suwannee alligator snapping turtle (Macrochelys suwanniensis) in the Suwannee River, Florida. Chelonian Conservation and Biology 21(1): 2-10.
Thomas, T. M., M. C. Granatosky, J. R. Bourque, K. L. Krysko, P. E. Moler, T. Gamble, E. Suarez, E. Leone, K. M. Enge, K.M. and J. Roman. 2014. Taxonomic assessment of Alligator Snapping Turtles (Chelydridae: Macrochelys), with the description of two new species from the southeastern United States. Zootaxa 3786(2): 141-165.
US Fish & Wildlife Service. 2024. Endangered and Threatened Wildlife and Plants; Threatened Status for the Suwannee Alligator Snapping Turtle with a Section 4(d) Rule. Federal Register 89(124): 53507-53528.
Thomas M. Floyd
T. M. Floyd, May 2025: original account
