It has been four months since the U.S. Fish and Wildlife Service declared two southwestern aquatic snakes threatened under the Endangered Species Act. Now, the Center for Biological Diversity has announced that it intends to sue the federal agency over its management of livestock grazing permits, saying they threaten the two listed snakes, the northern Mexican gartersnake and the narrow-headed gartersnake. The snakes are native to New Mexico and Arizona.
In a letter to the Forest Service issued Tuesday, the Center argued that livestock grazing threatens the narrow-headed gartersnake and the northern Mexican gartersnake by damaging the riparian areas those species call home. It continues that the Forest Service has failed to consult federal biologists in its management of those allotments, a process that is required because the snakes are now listed as threatened.
But while grazing may be one factor in the snakes’ decline, scientists who have studied the species for years say it’s much less of a threat than invasive species that eat the snakes’ babies and alter their habitat.
“The overwhelming effects (to the snakes) have to do with nonnative species,” said Philip Rosen, an assistant research scientist at the University of Arizona who has studied the snakes since 1985. “(Grazing is) definitely an impact but compared to the exotic species problem I would say it’s almost insignificant.”
The Center for Biological Diversity, an environmental nonprofit based in Tucson, also recognized that the threats to the snakes are diverse, including water withdrawals, groundwater depletion, agricultural and urban sprawl and nonnative species.
“These snakes have experienced massive range contractions and are already extinct from huge portions of their range, including the area where Phoenix have sprawled,” Jay Lininger, a senior scientist at the Center, said in an interview. “The threats are myriad, complex and intimately bound with our human civilization.”
But the potential impacts of livestock grazing are imminent, the Center said in a press release about its intent to sue. Cattle trample and eat streamside vegetation and degrade water quality, the Center argued.
Its letter names 170 permits that cover parcels where livestock grazing occurs within, adjacent to or immediately upstream of the snakes’ habitat. The parcels span six national forests across Arizona and New Mexico, including the Coconino, Apache-Sitgreaves and Prescott national forests.
The letter of the law
According to the Endangered Species Act, federal agencies are required to consult the U.S. Fish and Wildlife Service before taking actions that may impact a threatened or endangered species. Though many of the livestock grazing permits named in the Center’s letter were issued decades before the two snakes were listed, the Center argues that the Forest Service is still obligated to complete the consultation process.
Based on that scientific opinion, the Endangered Species Act requires that the Forest Service ensure that its actions don’t jeopardize the existence of listed species.
The small, greenish grey narrow-headed gartersnake lives in cool, clear, rocky streams where it feeds on fish. In the winter, the snakes hibernate in areas above the stream. The U.S. Fish and Wildlife Service found that 31 out of 41 known populations of the snake are “likely not viable” or are on the edge of extinction.
The outlook is as grim for the northern Mexican gartersnake. The federal listing decision found that 24 out of 29 populations were threatened with extinction. The northern Mexican gartersnake is olive colored with three yellow stripes running down its body and lives in larger streams with year-round flow.
The scientists speak
Instead of a lawsuit, the University of Arizona's Rosen said he would rather see collaborative work with ranchers to help protect gartersnake habitat.
“I’m dubious about putting a lot of pressure on the ranchers over this,” he said.
While studies do show negative impacts of grazing on other gartersnake species, there are no definitive data that show how the practice specifically impacts narrow-headed and northern Mexican gartersnakes, said Andrew Holycross, a professor at Arizona State University.
Even so, “there is no reason to think heavy grazing isn't going to affect these species as well,” Holycross said.
In addition to munching away at riparian vegetation the snakes use to hide from predators, livestock also can cause increased runoff and sedimentation in streams, he said. The snakes depend on clear water to see their aquatic prey.
A number of factors working synergistically have led to the steep declines in narrow-headed and northern Mexican gartersnake populations, Holycross said. But he agreed with Rosen that nonnative predators are the biggest threat to both species.
Erika Nowak is another longtime narrow-headed gartersnake researcher. An associate research faculty in biological sciences and herpetologist with the Colorado Plateau Research Station at Northern Arizona University, Nowak has been researching the species intensely since 1999 and has paid particularly close attention to the population of narrow-headed gartersnakes in Oak Creek Canyon since the Slide Fire this summer.
Grazing isn’t an issue for the snake populations in Oak Creek, Nowak said. She also spoke highly of the Forest Service’s efforts to work collaboratively in managing gartersnakes and actively supporting the species’ recovery. She spoke from experience working with the agency on snake projects in Arizona and New Mexico.
Local Forest Service officials didn’t comment on the issue due to the pending lawsuit.