Utah’s tortoise population in free fall, scientists warn

Wildlife biologists blame drought, wildfires, habitat loss and human activity.

St. George • After nearly three decades of concerted efforts to save them, the Mojave Desert tortoise in southern Utah is more threatened than ever.

In 1990, the Mojave Desert tortoise was listed as a threatened species under the federal Endangered Species Act. Six years later the Red Cliffs Desert Reserve, which now includes the Red Cliffs National Conservation Area, was created on 62,000 acres north of St. George to help recover desert tortoises threatened by development and habitat loss.

Despite those efforts, the prognosis for the recovery of the species is more grim than ever. According to Utah Division of Wildlife Resources officials, adult desert tortoises in the core area of the reserve — prime habitat between State Route 18 and Interstate 15 — have dropped from 33 per square kilometer in 1998 to about 12 per square kilometer in 2019. The results from a 2023 survey are still being tabulated.

“Tortoises have declined more than 50% within the core of the reserve,” said Ann McLuckie, a biologist with the Utah Division of Wildlife Resources.

The Mojave Desert tortoise is found west of the Colorado River, primarily in southern Utah, northern Arizona, Nevada and California. McLuckie said wildlife officials can’t speak to adult tortoise populations outside the reserve because those areas are not monitored. Moreover, she noted, only adult tortoises are counted because the juveniles are expert hiders that are too small and hard to find.

Glueing shells back together

Still, what wildlife biologists do know about southern Utah’s desert tortoise is cause for concern. McLuckie ticks off the usual suspects behind the reptiles’ decline — drought, wildfires, habitat loss and human activity.

In 2002, she said, a large number of tortoises — some with diseases or otherwise compromised — died due to a dramatic drought. Many more desert tortoises died due to a 2005 and subsequent wildfires, most recently in 2020, that swept through the reserve.

McLuckie said many tortoises died from direct exposure to the hot temperatures, and others indirectly from the loss of plant cover that provides shade or shelter from the heat. Moreover, the fires have destroyed native shrubs and grasslands on which tortoises like to forage.

Much of the native vegetation has been replaced by invasive cheatgrass and red brome, introduced in the United States in the mid-1800s from the Mediterranean region, which are known to increase the frequency and intensity of fires.

“Post-2005 fires, the population has never rebounded to its former level, which was the 1998 period,” McLuckie said.

Human activity, especially in the form of vehicular traffic is another factor in tortoise mortality. Over the past year, McLuckie said, vehicles have killed 12 desert tortoises and injured two more, which a St. George veterinarian was able to save by using epoxy to glue their shells back together. Fences along roads in the reserve help reduce such collisions but are often undercut by erosion caused by wind and erosion.

A highway to hell for tortoises?

Another cause for concern is the proposed North Corridor Highway, a four-lane highway that would cut through about 4.5 miles of the Red Cliffs National Conservation Area. The right of way for the road was approved in January 2021 during the Trump administration.

However, due to some issues with the initial environmental impact statement, U.S. District Court Judge Amy Berman put that approval on hold in November while federal agencies take another look at the proposed highway and conduct a supplemental environmental impact statement that would build upon the original.

State and local officials argue the Northern Corridor is needed to ease traffic congestion in St. George during peak travel times. By the Dixie Metropolitan Planning Organization’s calculations, the highway through the reserve would carry 25,000 vehicles a day, reduce traffic delays by 300,000 hours a year and reduce congestion by as much as 15%.

If the highway is built, environmentalists fear for the tortoises’ future.

“The proposed location of the northern corridor highway cuts through lands that were specifically protected as mitigation for development of Mojave Desert tortoise habitat elsewhere in the county,” said Holly Snow Canada, executive director of Conserve Southwest Utah. “The proposed highway would strike through some of the most important Mojave Desert tortoise habitat in the recovery unit for the entire species, counteracting the significant investments by the Bureau of Land Management, Fish and Wildlife Service and others for the recovery of this remarkable reptile.”

Dead zones

Biologists have determined the Northern Corridor would negatively impact 4,250 meters on each side of the highway or a combined 15,000 acres of critical tortoise habitat. Biological consultant Ed LaRue, a member of the California-based Desert Tortoise Council, said similar roads in California have created dead zones where tortoises are noticeably absent and foresees the same thing happening if the Northern Corridor is constructed.

He recalls two 80-acre parcels in California in particular, one of which was bisected by U.S. Route 66.

“The tortoises disappeared from the parcel where the road went through it but there were still lots of them in the adjacent 80-acre parcel,” LaRue said, adding he also examined 17 plots on the east side of California’s Highway 395, each one of which had become a dead zone devoid of desert tortoises.

Despite the looming threats, McLuckie and others remain optimistic that state and federal agencies can recover the species to pre-2005 fire levels. The BLM has a “containerized plant project” that takes creosote, globe mallows and other native plants grown at a Las Vegas nursery and plants them on the reserve. In addition, state wildlife officials are conducting aerial seeding on burn areas and applying herbicides to reduce the fire risk posed by invasive vegetation.

Lest anyone deem such efforts to be excessive, McLuckie and LaRue insist the Mojave Desert tortoise is worth saving.

“The tortoises are a sentinel or umbrella species in the sense that if their numbers are declining it [warns] us about the state of our lands and the health of our planet,” she said. “It’s important to protect the species so that we can have a healthier planet.”