ST. GEORGE — The Mojave desert tortoise is uniquely adapted to survive the temperature extremes Washington County’s red desert is known for, but some residents question: Are they native to Southern Utah or were they transplanted to the area by humans?

Considered a threatened species, the Mojave desert tortoise is federally protected, prompting habitat conservation, laws preventing the handling and ownership of wild tortoises and other protective measures.

While some have claimed tortoises are not native to the area, Mike Schijf, a biologist with the Red Cliffs Desert Reserve, told St. George News the reptiles likely inhabited the region prehistorically.

Multiple studies have evaluated the genetic composition of Mojave desert tortoises throughout their habitat, Schijf said, adding that he corresponded with genetic researchers from the University of Nevada in Reno on the subject.

These studies reportedly found that there are no significant genetic differences between Upper Virgin River and Beaver Dam Slope tortoises, Schijf said. The Upper Virgin River recovery area includes tortoises in Red Cliffs Deserve Reserve, and Beaver Dam Slope includes a population near state Route 91 in the southwest corner of Washington County.

The sample of tortoises from the Beaver Dam Slope region included in the researcher’s final results was small, but Schijf said that it appears most individuals located east of Lake Mead belong to the same genetic cluster.

Some of the reptiles in the St. George area may have ancestors from other parts of the tortoises’ range, as evidenced by the genetic mixture of these individuals with individuals further west in the Central Mojave Desert, Schijf said, adding it would appear that these reptiles bred with native tortoises already present in the region.

Ann McLuckie, a wildlife biologist with the Utah Division of Wildlife Resources, said the idea that tortoises are not native to Washington County has been a local “urban legend for quite some time.”

“But basically, yes, we do know that tortoises are native in this area,” she said.

Referencing a 2018 study, which can be found on Nature Portfolio, McLuckie reiterated that the Upper Virgin River tortoises are genetically related to each other, are closely related to their nearest neighbors on the Beaver Dam Slope and are more distantly related to those on the opposite side of the range in California.

This is what would be expected of a native population, she added.

Marshall Topham, a professor of environmental science at Utah Tech University, told St. George News he wrote an essay on the subject after hearing locals suggest the tortoises aren’t native. He said the suggestion that Southern Utah’s dense tortoise populations resulted from a few hundred people toting the reptiles into St. George is “laughable.”

“This notion is clearly refuted by basic animal population science,” he wrote in his essay. “It illustrates a misunderstanding of the science of evolutionary biology as it applies to animal populations, particularly populations of Mojave Desert Tortoise. … It is impossible for the demographics of the current population to be the result of displaced tortoises. Such a conclusion could not be supported by science for several reasons.”

Current population numbers and age distributions indicate a population that has developed over thousands of years as tortoises take 15-20 years to reach reproductive maturity and produce a small number of hatchlings per year, with a survival rate of approximately 5%, Topham said.

“A deliberate attempt to create an isolated population with the demographics we see today would have failed even if many hundreds of tortoises were released for many years for that very purpose,” he wrote. “Translocated tortoises often suffer a significant degree of mortality (loss of life) when introduced to a new environment, further challenging the claim that the tortoises in our area are not native.”

McLuckie said Mojave desert tortoises are found across a continuous range from California to Arizona, adding that there isn’t a physical barrier that would have prevented them from being present in Southern Utah.

Topham said there are natural pathways that would allow tortoises to move through their range, and it’s not uncommon for the species to live at elevations of 4,000 feet.

For instance, the animals could have migrated through the Virgin River Gorge from the Beaver Dam Slope to Cedar Pocket to St. George, where live tortoises and remains have been found. Or they could have used a corridor linking Bloomington to the Beaver Dam Slope via “a low elevation pass located South of the Apex Mine and connections to the ‘Woodbury Hardy Desert Study Area.'”

“Long before pioneers arrived, Washington County was inhabited by Native Americans,” he added. “They are known to have transported Desert Tortoises with them. They used them for food and converted their shells into musical instruments and other ceremonial regalia. It is logical to assume they moved tortoises to the outer limits of the Mojave Desert and beyond.

“Even this known potential influence in tortoise distribution is not enough to explain the current population of tortoises present in the area. Tortoise influence on local Native American culture in the area can be seen depicted in local rock art and in discovered tortoise remains associated with ancient Native American dwellings.”

Evolving in the Mojave

Upper Virgin River tortoises are “uniquely adapted to living on the northeastern edge of their range,” as these populations experience temperature extremes, McLuckie said.

Washington County is at the convergence of three geographic provinces: the Colorado Plateau, the Great Basin Desert and the Mojave Desert. Tortoises are found at the edge of the Mojave Desert, but this isn’t the case where the desert ends to the north, McLuckie said.

Topham said that tortoises, as indicated by carbon dating, have been present in the Mojave Desert for at least 15 million years, along with other species unique to the ecosystem, like creosote bush.

Desert tortoise conservation

The Mojave Desert tortoise is listed as threatened under the Endangered Species Act due to ongoing threats, such as lost, degraded or fragmented habitat, wildfires, disease and road mortality, according to the United States Fish and Wildlife Service’s website.

The reptiles are a “really big part of the desert food web,” said Ammon Teare, the Red Cliffs Desert Reserve outreach coordinator. When young, tortoises are vulnerable and serve as a nutrition source for predators like coyotes, ravens and snakes.

“If they were to all just to go extinct, at least in this area, who knows what effect that would have on the higher-order predators that rely on tortoises for their sustenance,” he said.

Additionally, tortoises dig burrows that are used by other animals. For instance, burrowing owls, which are considered a sensitive species, don’t typically build their own and utilize those created by tortoises for shade, shelter and to hide from predators, Schijf said.

To protect the Mojave desert tortoise and other sensitive local species, 62,000 acres of land were set aside in 1996 to create the Red Cliffs Desert Reserve, which is still expanding with the recent addition of Zone 6, located west of the Bloomington area and south of Santa Clara. However, there has been some controversy related to this area and the proposed Northern Corridor Highway.

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