WASHINGTON (CN) - Touting a conservation collaboration between federal and state agencies and landowners, the U.S. Fish and Wildlife Service announced the Sonoran desert tortoise does not merit federal protection. The agency's determination that listing the species under the Endangered Species Act is not warranted at this time was met with skepticism by the WildEarth Guardians environmental advocacy group that petitioned the USFWS to provide federal protection for the tortoise in 2008.
"It's unclear whether the service adequately considered the impacts of threats like grazing and ORV [off-road vehicle] use on our public lands, especially combined with drought and climate change," Taylor Jones, endangered species advocate for WildEarth Guardians, said. "And while it is important to acknowledge uncertainty regarding climate change impacts, the service has a disturbing history of using small amounts of uncertainty to deny needed protections to species facing clear threats."
The USFWS has collaborated with species experts from public and private sectors to complete a status assessment that purports to forecast the species' condition over the next 100 years. The assessment looked at the six risk factors of altered plant communities, altered fire regimes, habitat conversion of native species to agriculture or urban developments, habitat fragmentation, human-tortoise interaction and climate change.
"While these stressors can affect individual tortoises, our analysis and modeling of, and with, available data did not find conclusive evidence that population declines have persisted or are likely to in the foreseeable future," the agency said.
The desert tortoise was determined to be a candidate for listing in 1982, and in 1990, the Mojave population was listed as a threatened species. The Sonoran population was considered to be a distinct population segment at that time and it was only protected if it was found outside its usual range, due to the similarity of appearance with the Mojave tortoise. New genetic information in 2011 elevated the Sonoran population to a separate species, and it was reaffirmed as a candidate species with the taxonomic change in 2012.
The Sonoran tortoises, which are found mainly in Arizona and Sonora, Mexico, are measured by carapace, or top shell, length, and usually considered to range from 8 to 15 inches, though one adult male topped 19 inches in a 1980 survey. They may weigh up to 15 pounds, and they eat a variety of vegetation, including cactus.
Invasive non-native plant species, especially grasses, not only alter forage opportunities for the tortoises, but also affect plant cover used for heat-regulation and protection from predators. Non-native grasses also increase wildfire risk.
Conversion of habitat to agriculture and development fragments the tortoise's range and prevents movement between populations. "One study found that adult tortoise survivorship has been shown to improve with increasing distance from urbanized areas; specifically, the odds of a Sonoran desert tortoise surviving 1 year increases 13 percent for each 6.2-mile increase in distance from a city of at least 2,500 people," the action noted. However, 29 percent of the tortoises' Arizona habitat occurs within 12 miles of urban areas.
The collaboration between Arizona, the Bureau of Land Management, Department of Defense and the National Park Service protect an estimated 73 percent of tortoise habitat in the state. "Our Species Status Assessment, a tool we did not have previously, showed that our federal land-management partners have been managing this species for more than 30 years, and doing it well," Steve Spangle, Arizona field supervisor for the service, said. "With this track record, we are confident that the tortoise will continue to thrive. When we can conserve species without listing under the ESA, everybody wins, including the tortoise."
The WildEarth Guardians disagree, maintaining the ESA is an important defense against the current extinction crisis, where species are disappearing at a rate much higher than the natural rate of extinction due to human activities. "Scientists estimate that 227 species would have gone extinct if not for ESA protections. Without ESA protections, desert tortoises are in greater danger of extinction," the group said.