Understanding the Distribution of Suwannee Alligator Snapping Turtles

Adult Suwannee Alligator Snapping Turtle – Houston Chandler

Alligator snapping turtles are one of, if not the, most impressive reptile species native to the southeastern United States. Adults can reach weights easily exceeding 100 pounds and shell lengths in excess of two and a half feet. A true leviathan when living in relatively small water bodies that characterize much of the eastern portion of the alligator snapping turtle’s distribution. The eastern end of the alligator snapping turtle’s range is occupied by the Suwannee Alligator Snapping Turtle (Macrochelys suwanniensis), which inhabits only the Suwannee River drainage in Georgia and Florida. This relatively small distribution combined with a history of unsustainable commercial harvest on alligator snapping turtles has led to significant conservation concern for this species (Pritchard 2006). Large-scale commercial harvest is now illegal in Georgia and Florida, but alligator snapping turtles are still susceptible to unnecessary mortality resulting from fishing activity along rivers. It is not uncommon to find turtles with fish hooks in their mouths or digestive tract, and turtles are sometimes drowned on long lines when they are unable to surface to breathe. It became apparent in 2016 (a couple of years after M. suwanniensis was described; Thomas et al. 2014) that there was a significant need for better survey data to inform conservation decisions for this species.

Young alligator snapping turtle with a fish hook imbedded in its mouth. The hook was removed before release. – Houston Chandler

To fill this knowledge gap, The Orianne Society has been working alongside several partners to survey for Suwannee Alligator Snapping Turtles in as many locations as possible across their distribution. Alongside former Orianne biologist, Dirk Stevenson, we worked to survey water bodies in Georgia, while Florida Fish and Wildlife Conservation Commission oversaw the Florida work. So how do you catch these large turtles that typically live in murky water and are most active at night?

Placement of large traps often becomes difficult during dry summer months – Houston Chandler

A typical day in the field started early in the morning loading up traps and getting ready for a day on the water. Trapping with large (4’ diameter) hoop-nets is the most common method used to survey for alligator snapping turtles. Traps are set in sections of the stream that have habitat potentially suitable for turtles (e.g., undercut banks or large debris piles where turtles can shelter). Hoop-nets are typically placed with a small air pocket allowing trapped animals a place to breathe. Baiting these traps is the worst part of an otherwise enjoyable day in the field. Alligator snapping turtles eat fish, and the best bait seems to be a variety of smelly fish, all stuffed into plastic water bottles and suspended within the trap. Not so bad going in but after two days in the water the smell deteriorates into about what you would expect. But that’s about the only negative thing I have to say about trapping for these turtles. Trapping surveys are always fun (you never know what you are going to catch!) and spending hot summer days on the water is about as good as it gets for fieldwork in Georgia.

Trapping for alligator snapping turtles can generate some interesting bycatch. – Dirk Stevenson

In total, over 1,300 trap nights have been conducted targeting Suwannee Alligator Snapping Turtles since 2011 (much of this effort occurring over the last 4 years). Over 200 turtles have been captured during these surveys, many from water bodies or counties without previous records of alligator snapping turtles. Captures per unit effort varied substantially across the study area, with more turtles typically being captured in the Florida portion of the range. M. suwanniensis seems to be either extirpated or extremely localized in the mainstream Suwannee River in Georgia. We failed to trap a single turtle from this river in Georgia despite targeting it with multiple trapping events. Interestingly, there continue to be rare sightings of alligator snapping turtles from the Okefenokee Swamp. The status of the species within the swamp remains unclear, and this water body is difficult to survey because of the number of American Alligators present. Finally, juvenile or sub-adult turtles were captured on several surveys in various water bodies, indicating that recruitment to these populations is still occurring. Recruitment into the populations at least provides anecdotal evidence that populations may be able to sustain themselves. The results of our survey work are currently being prepared for publication. Be on the lookout for the full write-up in the near future!

Suwannee Alligator Snapping Turtle sitting on the stream bank prior to release – Houston Chandler

What does the future hold for Suwannee Alligator Snapping Turtles? This is a challenging question to answer even with an expanded understanding of where extant populations occur. The U.S. Fish and Wildlife Service has been petitioned to list alligator snapping turtles on the Endangered Species List, and the Species Status Assessment predicted that populations would continue to decline in abundance and range (USFWS 2020). These predictions are characterized by large amounts of uncertainty, and we still know relatively little about the population biology and ecology of these incredible animals. Additional research is clearly needed to understand the effect of an ever changing world on Suwannee Alligator Snapping Turtle populations. These turtles have clearly benefited from a ban on commercial harvest, but strengthening protections for freshwater ecosystems would further ensure that these giants persist as a source of wonder and amazement.

Literature Cited

Pritchard, P. C.  2006. The Alligator Snapping Turtle: Biology and Conservation. Krieger Publishing, Malabar, Florida, USA, 140 pp.

Thomas, T. M., M. C. Granatosky, J. R. Bourque, K. L. Krysko, P. E. Moler, T. Gamble, E. Suarez, E. Leone, K. M. Enge, 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 3786:141–165.

U.S. Fish and Wildlife Service. 2020. Species status assessment report for the Suwannee alligator snapping turtle (Macrochelys suwanniensis), Version 1.0. February 2020. Atlanta, GA, 158 pp.

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