Sequoyah National Wildlife Refuge in eastern Oklahoma has begun a health assessment to pinpoint why the number of alligator snapping turtles has declined substantially over the past decade.

Historically, the refuge has supported a rich turtle community, including alligator snapping turtles, which have been in decline for years elsewhere in Oklahoma. Sequoyah Refuge was one of the few places in the state with a robust alligator snapping turtle population that had been used as brood stock for reintroduction efforts.

However, over the past decade that alligator snapping turtle population has collapsed. Research indicates that entire age classes from this 10–year period are missing. Biologists are baffled about the cause. In addition, carcasses of box turtles are appearing, suggesting that there may be a disease outbreak.

“In short, not only did the alligator snapping turtle populations decline, so did the entire turtle community,” says Sequoyah Refuge wildlife biologist Dustin Taylor. “The decline in alligator snapping turtles is especially alarming if you consider that Sequoyah Refuge contained one of the two populations thought to be stable in eastern Oklahoma.”

In response, the refuge, the National Wildlife Refuge System Inventory and Monitoring program, Missouri State University and the Tulsa Zoo are taking action. Led by Missouri State assistant biology professor Day Ligon and graduate student Jay Krystyniak, they are collaborating on a turtle health assessment. They are monitoring alligator snapping turtles, three–toed box turtles, red–eared sliders, Mississippi muds and common snapping turtles.

Sequoyah Refuge offers excellent habitat alligator snapping turtles, which are endemic to waterways that ultimately flow into the Gulf of Mexico. The 20,800–acre refuge is on Kerr Reservoir, where the Canadian and Arkansas Rivers meet. It includes riverfront and floodplain forest, floodplain sloughs and oxbows, managed wetlands, cropland and about 7,500 acres of open water in the reservoir.

Largest Freshwater Turtle

The alligator snapping turtle is North America’s largest freshwater turtle. It is known for its large, “snapping” jaw, which it uses to warn off predators and catch prey. It is almost entirely carnivorous. The species, which can live to 100 years in the wild, is secretive and mostly aquatic, with the exception of rarely observed basking.

The health assessment is capturing turtles in baited commercial hoop traps. It targets creeks that historically had the highest turtle populations as well as several managed wetlands on the refuge.

Two such creeks exemplify the decline.

Data from a baseline survey conducted in 1997–2000 show there were an estimated 127.5 to 152 alligator snapping turtles in Big Vian Creek. In 2010, the estimate was 22. In 2011, it was 50. In 2012, it rose to between 111 and 171.4, but that numerical range appears to have been artificially high, possibly because of favorable trapping conditions and movement among creeks.

A similar survey shows there were 68.4 to 86.6 alligator snapping turtles in Little Vian Creek in 1997–2000. By 2010, the estimate was 38 to 54. In 2011, it was 12 to 14.7.

All the while, capture rates for all turtle species have declined, most noticeably for red–eared sliders and alligator snapping turtles.

To determine if disease is a factor, the scientists are taking white blood cell counts and looking for the presence of specific viral antibodies as well as endo– and ecto–parasites.

“If one or more pathogens are at work,” says Taylor, “it is possible that turtles, amphibians or fishes could be serving as reservoirs for these pathogens.”

Nicole Haskett–Osborn is a public affairs specialist in the Southwest Region office in Albuquerque.