‘Dinosaurs of turtle world’ count on rivers for survival

"If something catastrophic were to occur, such as a chemical spill or something that affects the entire river, it could potentially devastate this species," says Travis Thomas. "The turtle is extremely limited by its habitat. All it has is this river and it has nowhere else to go." (Credit: Gary Tucker/USFWS/Flickr)

Conservation of coastal rivers of the northern Gulf of Mexico is vital to the survival of the alligator snapping turtle, scientists say.

A new study shows that the largest freshwater turtle in the Western Hemisphere, previously believed to be one species, is actually three separate species.

[related]

The limited distribution of the species, known to weigh as much 200 pounds, could potentially affect the conservation of rivers the turtles inhabit, including the Suwannee, says lead author Travis Thomas, a Florida Fish and Wildlife Commission scientist and former Florida Museum of Natural History volunteer, who began the research as a University of Florida wildlife ecology and conservation student.

“We have to be especially careful with our management of the Suwannee River species because this turtle exists only in that river and its tributaries,” Thomas says.

“If something catastrophic were to occur, such as a chemical spill or something that affects the entire river, it could potentially devastate this species. The turtle is extremely limited by its habitat. All it has is this river and it has nowhere else to go.”

Three separate species

In the study published in the journal Zootaxa, scientists revised the genus Macrochelys, often called the “dinosaurs of the turtle world” by lay people, to include Macrochelys temminkii and the two new species, Macrochelys apalachicolae and Macrochelys suwanniensis.

Restricted to river systems that drain into the northern Gulf of Mexico, the species are divided by geography, which led to differences in genetics, says co-author Kenneth Krysko, a herpetologist with the Florida Museum.

M. temminkii is found in river drainages such as the Mississippi and Mobile, while M. apalachicolae is confined to the Apalachicola and other Panhandle rivers,” Krykso says. “There are no alligator snapping turtles in the seven rivers between the Suwannee and Ochlockonee (Aucilla, Econfina, Fenholloway, Saint Marks, Steinhatchee, Wacissa, and Wakulla).

“This gap creates a geographic isolation that has likely resulted in the Suwannee species being the most genetically and morphologically distinct of the three Macrochelys lineages.”

These turtles were heavily harvested in the past for human consumption, which decimated populations from Texas to Florida, in part because of the species’ low offspring survival rate.

100-year-old turtles

M. suwanniensis populations are higher than previously believed, according to Florida Fish and Wildlife surveys of the Suwannee River during the past three years. The species’ survival remains a concern due to its restricted range and Florida law prohibits the possession, capture, and pursuit of alligator snapping turtles.

“We hope the new study leads to greater conservation efforts and management plans customized to protect each individual species,” Thomas says. “The key to conserving these species is to protect their habitats. If we protect the rivers, that is the biggest step toward protecting the wildlife that depend on them, especially in the case of the Suwannee species.”

Researchers examined the fossil record from 15-16 million years ago to the present and found morphological and genetic variations among the three species. Distinct variations were documented in the carapace, or shell, which can be easily observed in both living and fossil specimens.

“The western group (M. temminckii) is morphologically more primitive, but genetics testing suggests that the Suwannee snapper has a deeper divergence,” says study coauthor Jason Bourque, a vertebrate paleontologist with the Florida Museum of Natural History,

“When alligator snappers show up in the fossil record, they look a lot like modern alligator snappers. They do not start showing up in the fossil record until the early Miocene, but snapping turtles as a group go back to the late Cretaceous.”

With their spiked shells and scaled bodies, the prehistoric-looking reptiles can live up to nearly 100 years, but it is their amazing size that has drawn peoples’ attention for centuries, Thomas says. As large, apex predators, alligator snappers play an important role in the wild. A river ecosystem deprived of its alligator snappers would most likely experience negative implications.

Researchers from Duke University, University of Vermont, University of Minnesota, and the Florida Fish and Wildlife Commission contributed to the study.

Source: University of Florida