Macrochelys suwanniensis, 133

Macrochelys suwanniensis Thomas, Granatosky, Bourque, Krysko,
Moler, Gamble, Suarez, Leone, Enge, and Roman 2014 – Suwannee Alligator Snapping Turtle

Travis M. Thomas¹, Kevin M. Enge², Dirk J. Stevenson³, and Gerald R. Johnston⁴

¹Department of Wildlife Ecology and Conservation, Nature Coast Biological Station,
University of Florida, 110 Newins-Ziegler Hall, Gainesville, Florida 32611 USA [[email protected]];
²Fish and Wildlife Research Institute, Florida Fish and Wildlife Conservation Commission,
1105 SW Williston Road, Gainesville, Florida 32601 USA [[email protected]];
³Altamaha Environmental Consulting, 414 Club Drive,
Hinesville, Georgia 31313 USA [[email protected]];
⁴Department of Natural Sciences, Santa Fe College, 3000 NW 83rd Street,
Gainesville, Florida 32606 USA [[email protected]]

Summary. – The Suwannee Alligator Snapping Turtle, Macrochelys suwanniensis (family Chelydridae), is a large, aquatic freshwater species that is genetically and morphologically distinct from other Macrochelys populations. The species is endemic to the Suwannee River drainage in southern Georgia and northern Florida, where it occupies the mainstem Suwannee River and most of its larger streams and tributaries. However, it is considered rare in the headwaters, including the extreme upper Suwannee River and Okefenokee Swamp. A capture-recapture study in the mainstem Suwannee River suggests high annual adult apparent survival (0.99) and estimated the population size to be ~1,200–2,700 individuals (~7 turtles per river km). Despite these findings, the population trend is considered uncertain, potentially stable or slightly declining. Population structure, sex ratios, densities, and mean body size vary across sites, likely reflecting natural variation in riverine habitat and resources availability in the Suwannee drainage. Males tend to reach much larger sizes in the more biologically productive sections of the Suwannee and Santa Fe rivers. The high proportion of large males (≥45 kg) indicates that the Suwannee drainage was likely spared from past commercial and local overharvest, which has plagued other Macrochelys populations. A study in the upper and middle sections of the Suwannee River found home range size to be individually variable and temporally dynamic in response to water levels. Turtles move linearly within the river channel and utilize bank-associated habitats such as woody debris and undercut banks, but during flooded conditions, turtles move laterally into the floodplain, likely to access new resources that are generally unavailable. Reproductive biology and diet remain poorly understood but may resemble those of M. temminckii, the Western Alligator Snapping Turtle. Although possession and harvest are illegal, incidental mortality from ingested fishing hooks and entanglement in bank-set fishing gear poses a significant threat to populations. Recent research indicates that ~10% of radiographed individuals were found to have ingested fishing hooks lodged in the throat or gastrointestinal tract, potentially posing a significant health risk. This is an immediate conservation concern because M. suwanniensis populations can rapidly decline due to small increases in adult mortality. Over the long-term, increasing water withdrawals, decreasing water quality, and frequent sewage spills represent emerging threats to population persistence. Macrochelys suwanniensis is considered Threatened in both Florida and Georgia, and recently the U.S. Fish and Wildlife Service also listed the species as federally Threatened under the Endangered Species Act.

Distribution. – USA. Endemic to the Suwannee River drainage in southern Georgia and northern peninsular Florida.

Synonymy. – Macrochelys suwanniensis Thomas, Granatosky, Bourque, Krysko, Moler, Gamble, Suarez, Leone, Enge, and Roman 2014.

Subspecies. – None recognized.

Status. – IUCN 2025 Red List: Vulnerable (VU C1; assessed 2025); CITES: Appendix II (USA, as Macrochelys temminckii [sensu lato]; assessed 2023); US ESA: Threatened (assessed 2024); Florida: Threatened; Georgia: Threatened.

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