Monday, November 26, 2012

The Alligator Snapping Turtle: Natural History, Mythology, and Conservation

The following article is a guest post by Brian Folt. Brian is a Ph.D. student at Auburn University, where he studies the community ecology of amphibians and reptiles. He grew up in the Midwest and received a B.S. from Ohio University in 2011. Brian conducts field research in the southeastern United States and Central America. Brian is an avid outdoorsman and a die-hard Cleveland sports fan. You can follow him on Twitter @brianf0lt.

     Here in the United States, few are aware that we actually live alongside one of the most species-rich turtle faunas in the world. Of 320 species known worldwide, 42 inhabit the southeast US, with a hot-spot of at least 18 known from the Mobile River Delta in Alabama. Only the Ganges River drainage in eastern India has a similarly-sized area with more turtle species (but just barely!).

     Turtles of the southeast vary drastically in ecology, natural
 history, and morphology. These animals inhabit a diverse spectrum of habitats, from well-drained pine forests, like the Gopher Tortoise, to high elevation bogs, like the tiny Bog Turtle. Of this diverse turtle fauna, perhaps the most remarkable species is the Alligator Snapping Turtle (Macrochelys temminckii). The largest freshwater turtle in North America, this species is also highly aquatic. Unlike classic riverine turtles which conspicuously bask on logs or shoreline, Alligator Snappers never leave the water to bask or move overland, except when females lay eggs (an annual occurrence) and juveniles move from these nests to the water.

      Alligator Snapping turtles are thought to be sit-and-wait predators: they hang out patiently on the river bottom with mouths agape, waiting for food to come to them. They possess a fleshy structure on the tongue, the lingual lure, which attracts fish or other prey to the jaws. When inquisitive prey touch the sensitive lure, the powerful jaws immediately snap shut, and the turtle receives a nice snack. Bon appétit!

      I spent last summer in the bayous of south Alabama trapping turtles with Jim Godwin, a biologist with the Alabama Natural Heritage Program at Auburn University. Jim is conducting a long-term study of the federally-endangered Alabama Red-bellied Turtle (Pseudemys alabamensis). During this work, however, we also became intimately familiar with Alligator Snappers, as we caught over 40 of these fascinating turtles.

     Throughout the summer, we had the pleasure to talk about our work with many local swimmers, kayakers, canoeists, fisherman, etc. Curious folks generally ask a series of questions regarding the Alligator Snapping Turtles, questions mired in mythology. Here are a few typical questions and the answers I often provide:

How big do they get? 

     Big! Really big. The largest records indicate that some 
male Alligator Snapping Turtle shells can reach 30 inches [0.76 m] long and some whoppers can weigh more than 260 pounds [118 kg]! That’s heavier than Cam, or four scooters. The largest individuals we’ve captured weighed approximately 150 pounds [68 kg]. Because males have different tail proportions and get much larger than females (females generally don’t get much bigger than 77 pounds [35 kg]), this species has what is called sexual dimorphism.

How long do the loggerheads live? 

      “Loggerhead” is a common name that many locals call the Alligator Snapping Turtle. This of course creates confusion because of the large, endangered sea turtle with the same name. Confusion aside, people always wonder how long Alligator Snappers live, and the answer is a long time. Some individuals have lived 70 years in captivity, but we really don’t know how long they live in the wild. Studies have counted rings on shell scutes (“annuli”) to estimate turtle age, not much unlike similar studies of trees or fish. The scute measurements indicate that individuals easily reach ages into the 40s, but estimates beyond this point are unreliable. More long-term mark-recapture studies are needed to determine how long this animal can live in the wild.

Are you going to eat them? 

     No! That’s illegal (and gross). All turtles are protected 
from collection in Alabama, and for good reason. Commercial harvest of Alligator Snapping Turtles in the 1960s and ‘70s by soup companies appears to have severely depleted populations throughout the species’ range. More recently, trappers have been exporting other local turtles to China, where they are highly valued for food and medicine. Because turtles are an important component of balanced freshwater ecosystems, we are attempting to protect and conserve them in Alabama.

But, what are the chances that I’ll be bitten while out for a swim? I’ve heard they can take your foot off! 

     While this may come as a surprise to many, the answer is none! As far as we know, there is no documented case of a hidden Alligator Snapping Turtle biting a swimming or bathing human that is minding their own business. Like most wild animals that encounter people, it seems that the first reaction of Alligator Snapping Turtles is to flee. For these reasons, I’m highly skeptical that an innocent swimmer will ever be bitten.

     Of course, if you pull one of these beasts out of the water, it’s a different story. Like all wild animals, these turtles will defend themselves when cornered and those jaws are no joke. Dr. Peter Pritchard’s classic monograph, The Alligator Snapping Turtle: Biology and Conservation, provides a photograph of a Florida citizen who lost the tips of his middle and ring fingers to a bite from a captive animal. If you are afraid of being bitten by an Alligator Snapper, don’t play around with them! The same concept applies to venomous snakes.

     Through our research efforts, we have learned much about the distribution and abundance of Alligator Snappers in Alabama, and answered a few interesting questions about the effects of historic commercial harvest on this species. In general, it seems that Alligator Snapping Turtles are currently rare in Alabama, but there are a few places where the species remains locally abundant. Unfortunately, despite legal protection in Alabama and throughout its range, this species is occasionally killed by abandoned fishing lines, such as limb-lines or trotlines. This has been a major cause of turtle mortality in Georgia and may inhibit the recovery of populations in Alabama. I urge fisherman, officials, and civilians to more closely monitor and regulate these fishing lines to reduce the by-catch and mortality of the Alligator Snapping Turtle, a truly magnificent component of our native wildlife.


Want to learn more? Check out these sources:

Buhlmann, K., Akre, T., Iverson, J., Karapatakis, D., Mittermeier, R., Georges, A., Rhodin, A., van Dijk, P., & Gibbons, J. (2009). A Global Analysis of Tortoise and Freshwater Turtle Distributions with Identification of Priority Conservation Areas Chelonian Conservation and Biology, 8 (2), 116-149 DOI: 10.2744/CCB-0774.1

No comments: