Missouri State University

Dr. Day Ligon

  • Associate professor of biology
  • Springfield, Missouri
  • PhD in Zoology, 2007, Oklahoma State University

A turtle's tale of survival

Few of us understand what is entailed in a species becoming listed as threatened or endangered under the Endangered Species Act, though most believe conservation efforts are noble.

Conducting research to aid the conservation of a species whose numbers have declined is often challenging precisely because of the difficulty in locating individuals. This can be especially true for animals that are secretive and therefore difficult to detect even in the best of circumstances.
Dr. Ligon reintroducing a turtle to a habitat
One such species is the alligator snapping turtle which, after decades of population declines, has been petitioned for federal listing as an endangered species three times. The most recent petition is currently under review by the U.S. Fish and Wildlife Service. These large turtles are of particular interest to Dr. Day Ligon, associate professor of biology at Missouri State University, who has published prolifically about them.

His specialty is reintroduction biology – a subset of conservation biology – that works to increase populations of animals by reintroducing them in their historic range to re-establish populations that can sustain themselves without human intervention.

Who’s to blame for this depressed number of alligator snapping turtles? According to Ligon, channelization of rivers and construction of dams have had huge impacts.

So, too, has people’s affinity for turtle meat. As other large species, such as sea turtles, were granted protection from commercial harvesting, pressure on alligator snapping turtles to fill this niche market increased. As a result, alligator snapping turtles were harvested at much higher rates than populations could sustain.

In practice, these and many other turtles are sensitive to even low harvest rates because they take so long to mature and begin reproducing. It can take decades for a population to recover from the removal of even a few large adults.

Below the surface

Alligator snapping turtles, which are endemic to the southeastern United States, can solely be found in the rivers that flow into the Gulf of Mexico.

"They’re big, impressive, ugly-but-charismatic turtles that almost nobody ever sees, because they’re so highly aquatic. They probably spend less time on land or basking on logs than any other freshwater turtle species in the United States," said Ligon.

Due to this aquatic nature, these turtles don’t move around dams easily. In the rivers that feed into the Gulf of Mexico, many dams exist, making it next to impossible for a population to become reestablished after it’s been cleared out. However, if the habitat is otherwise in good condition, animals reintroduced into these isolated river segments often can thrive.

Ligon, along with his graduate students, spend the summers at the Caney River on the Kansas and Oklahoma border and at Tishomingo National Fish Hatchery in southeastern Oklahoma – run by the U.S. Fish and Wildlife Service – studying the secret underwater lives of alligator snapping turtles. This progression of research projects, funded by more than half a million dollars since Ligon joined Missouri State’s faculty, continues to fill in gaps of knowledge, allowing for more informed conservation management decisions.

In 2002, Ligon joined forces with this fish hatchery, which at that time had 16 adult alligator snapping turtle in its captive breeding program. In 2008, they began releasing animals back into their natural environments. Now, they produce 500-600 hatchlings each year, keep them in captivity until they have grown and are less prone to predation, then release them into areas where the species has disappeared.

When the animals are released, Ligon and his team continue to gain information on critical research questions.

"We learn a lot about how many of them survive, how fast they grow and when they start reproducing," said Ligon. "Once we start seeing reproduction, and then ultimately recruitment of new animals into the population that we didn’t put there, that will be the point at which we can really start saying with some confidence that it seems to be working."

Learn more about Day's research in Mind's Eye.