Species Description
The Suwannee Alligator Snapping Turtle (Macrochelys suwanniensis) is a species of large freshwater turtle that is endemic to parts of Georgia and Florida in the southeastern United States. Suwannee Alligator Snapping Turtles are one of the largest freshwater turtle species found anywhere in the world. Adult male turtles can have straight-line carapace (shell) lengths exceeding 65 cm (25.5 in.) and weigh in excess of 57 kg (125 lbs.). Adult female turtles, while still large, are typically much smaller than males and rarely exceed 22 kg (48 lbs.). In addition to large body size, Suwannee Alligator Snapping Turtles have large heads and jaws, which they use to capture prey. The upper jaw is sharply pointed, and the head is triangular in shape when viewed from above.
Suwannee Alligator Snapping Turtles typically have dark brown shells and skin. In older individuals the skin around the head and neck often turns a pale yellowish or whitish color. Some individuals, especially young turtles, may have some faint light striping along the back of the head and neck. Most individuals have a variety of fleshy tubercles on the head and neck, but they are most prominent in young turtles. Apart from their large heads and jaws, the most distinctive feature of alligator snapping turtles are their robust shells with three sharp keels running from front to back. While the carapace (upper shell) is impressively thick and armored, the plastron (lower shell) is significantly reduced, so they cannot pull their legs inside their shells. Alligator snapping turtles also have strong muscular tails that extend well past the back edge of their carapace. The Common Snapping Turtle (Chelydra serpentina) is the species most frequently confused with alligator snapping turtles, and while they also have long armored tails, their heads are not as large and they lack the three pronounced ridges on their shells. Finally, Suwannee Alligator Snapping Turtles can be identified from other alligator snapping turtle species by the shape of the caudal notch (portion of the shell just above the tail), which is crescent-shaped and much wider in Suwannee Alligator Snapping Turtles when compared to the other species.
Taxonomy
Alligator snapping turtles have been the subject of taxonomic revisions in recent years. The species was originally described by Troost in 1835 and was considered a single species for over 170 years. However, recent analyses have split alligator snapping turtles into two well-supported species (M. temminckii and M. suwanniensis) with a third species (M. apalachicolae) still in question. These splits have been based on both morphometric and genetic data. The scientific name M. suwanniensis refers to the Suwannee River drainage where this species is found.
Distribution
As their name suggests, Suwannee Alligator Snapping Turtles can be found throughout the Suwannee River watershed, including many of its tributaries. The larger tributaries of the Suwannee River include the Santa Fe River, the Withlacoochee River, and the Alapaha River, each of which is fed by many smaller creeks and streams. In total, this watershed covers parts of northern Florida and south-central Georgia. Interestingly, recent observations of Suwannee Alligator Snapping Turtles have been made in the Okefenokee Swamp, and there are scattered reports of the turtle occurring in the swamp documented in the published literature. However, its status in the swamp remains unclear, and additional survey work is needed to clarify the eastern boundaries of the distribution.
Despite conservation concerns for this species, Suwannee Alligator Snapping Turtles can still be found throughout much of what appears to represent their historic range. One notable exception is the mainstem of the Suwannee River in Georgia, where multiple recent survey efforts have failed to document the species (though it has been found in smaller tributaries in this region).
Habitat
Suwannee Alligator Snapping Turtles can be found in a variety of aquatic systems associated with the Suwannee River watershed. This includes the mainstems of the Suwannee River and the larger tributaries, as well as smaller streams and side channels. In parts of their range, populations can be found in blackwater swamps, oxbow lakes, and artificial impoundments. Within aquatic systems, individuals often use a variety of microhabitats for foraging and refugia. These include areas in and around logjams or treefalls, undercut banks, cavities under large root masses, and other holes in the riverbanks. Turtles may preferentially select areas with high canopy cover.
While primarily aquatic, Suwannee Alligator Snapping Turtles are sometimes observed on land. This is usually associated with female nesting movements, which are closely tied to riverbanks and the immediately surrounding uplands. Other overland movements may occasionally occur, particularly during droughts when some habitats dry out or experience reduced water levels. However, such movements are rare in this species and not well documented.
Movement and Home Range
There have only been a small number of studies on movement and home range size in alligator snapping turtles. Linear home range estimates along river and stream corridors can extend several miles, although most day-to-day movements are likely much shorter (a few hundred meters). Over longer periods, individuals may move between main river channels and seasonally flooded habitats where food is plentiful. Home ranges are often centered around aquatic structures or other refugia to which turtles can reliably return.
Suwannee Alligator Snapping Turtles are primarily nocturnal and active year-round. As tracking technologies continue to improve in the coming years, we will likely learn much more about the aquatic habits of alligator snapping turtles.
Diet
Alligator snapping turtles have a varied diet that includes many taxa potentially encountered in their aquatic environments. Fish are a main component of their diet, and alligator snapping turtles are well-known for the worm-like lure attached to their tongue. When using this lingual lure, turtles lie motionless with their mouths open, making the lure twitch back and forth. If a fish makes contact with the lure or any part of the mouth, the jaws close with exceptional force, trapping the prey inside.
Freshwater mussels, clams, snails, and other turtles are also important food sources, and alligator snapping turtles easily crush them with bony plates located just behind the cutting edges of their jaws. Other potential prey, such as snakes, amphibians, water birds, crayfish, and carrion, may be taken opportunistically. There is also growing evidence that alligator snapping turtles regularly consume acorns, persimmons, and tupelo fruit that fall into the water.
Reproduction
Relatively little is known about reproduction in Suwannee Alligator Snapping Turtles. Mating occurs primarily during late winter or spring, and nests are typically laid in late spring (April or May). Female turtles usually nest close to the water (20–30 m), but on some occasions, eggs may be laid further away in surrounding upland habitats. Nest cavities are dug into sandy soils, often on raised berms or high riverbanks, to reduce the risk of flooding impacting nest success.
Clutch sizes generally range from 30 to 35 eggs but can approach 60 eggs in exceptionally large females. Alligator snapping turtles exhibit temperature-dependent sex determination, with higher temperatures producing a greater proportion of female hatchlings. It is unclear when Suwannee Alligator Snapping Turtles reach sexual maturity in the wild, but it likely takes at least 10 years, if not longer.
Conservation Concerns
Suwannee Alligator Snapping Turtles were recently listed as Threatened by the U.S. Fish and Wildlife Service under the Endangered Species Act. Historically, the main threat to alligator snapping turtle populations was extensive commercial harvest, primarily for turtle soup. Although commercial harvest of this species has been prohibited for several decades, legacy effects likely persist. The removal of adult turtles can be detrimental to populations because of their reliance on long-lived adults and delayed sexual maturity. Some studies suggest that thousands of adult turtles were removed from the wild over a relatively short time span. Today, illegal collection likely still occurs, but on smaller scales than during the era of commercial harvest. Some incidental mortality may also result from interactions with fishing activities, particularly trotlines or bush hooks that are left unattended. Additionally, turtles may be struck by boat propellers in some water bodies.
While many of the water bodies inhabited by Suwannee Alligator Snapping Turtles remain relatively intact (especially compared to other habitats in the Southeast), there are concerns about degraded habitat quality. Pollution from urban development and agricultural activities can reduce water quality, potentially impacting turtle populations and their food sources. Hydrologic modifications have been extensive across southeastern waterways, and the long-term effects of altering these fundamental processes are unclear.
Conservation concerns for Suwannee Alligator Snapping Turtles are heightened because of their restricted range. Recent survey results for the species have been mixed, but relative abundance estimates in many locations have been low. This may reflect a legacy effect of the extensive harvest that occurred in the 1970s and 1980s. Populations could continue to increase with appropriate protection and management. Overall, the relatively recent description of this species and the secretive nature of alligator snapping turtles underscore the need for more research to support informed conservation and management decisions.