By Jim Owen

The U.S. Fish and Wildlife Service has added two rare types of garter snakes to the list of "threatened" animal species that qualify for protection under the Endangered Species Act.

The narrow-headed and northern Mexico garter snakes reportedly live in some drainages of the Gila and San Francisco rivers in Grant, Catron and Hidalgo counties.

Researchers have determined that the biggest threats to the snakes are water sedimentation resulting from erosion, fires and livestock grazing; and competition for prey by invasive species like the American bullfrog, sunfish and bass.

Non-native crayfish feed on the snakes, and vegetation loss along streams resulting from grazing leaves them vulnerable to predation, according to the USFWS.

In 2007, a recovery plan drafted for the New Mexico Department of Game and Fish stated that "the majority of the populations" of the narrow-headed species were on national-forest lands. However, the document acknowledged that "potential habitat might be found on private property."

Surveys conducted at 16 sites a decade ago concluded that the "most robust population" of narrow-headed garter snakes were in Whitewater Creek (part of the Gila National Forest, in Catron County). The stream was "the least impacted by livestock grazing or non-native species," according to the recovery plan. Officials did cite off-road-vehicle use in the creek as a threat to the snake.

The number of narrow-headed garter snakes in the San Francisco River near Pleasanton was considered "robust" in the 1990s. By 2007, none of the snakes could be found in the area. During that period, throughout the Gila and San Francisco basins, the populations reportedly "declined significantly."

The status of the northern Mexican garter snake in New Mexico is even less certain. The government says some of the amphibians "may still occur" in the Gila River and Mule Creek, as well as in numerous Arizona streams.

The Center for Biological Diversity, which sued the government to list more animals under the provisions of the Endangered Species Act, praised the USFWS decision.

"Protecting (the two snakes), and the shrinking waters of the Southwest, will benefit every other animal that depends on these river systems," Collette Adkins Giese, an attorney with the organization, said in a news release.

Livestock producers and others are concerned that federal protections could mean restrictions on certain land uses. Wherever a viable population of one of the snakes is found, authorities could ban any practices that imperil the species' recovery.

Grazing cattle along streams in national forests has been banned since 2003. But, on private property, livestock often depend upon creeks and rivers. The Endangered Species Act does contain an exemption for the "operation and maintenance of livestock tanks or impoundments on private, state and tribal lands maintained by cattlemen as livestock watering holes," the Fish & Wildlife Service noted in a news release.

The federal act has been a political lightning rod since its inception more than 40 years ago. Supporters maintain that land-use restrictions are necessary to preserve rare species and habitats. Opponents say such laws violate private-property rights, and amount to unconstitutional "takes" of property.

Both of the newly classified snakes are non-venomous, and prey mostly on native fish like the speckled dace. They also eat invasive species such as rainbow trout, and occasionally consume a frog or toad.

"The northern Mexican garter snake can grow to 44 inches, and often occurs along the banks or in the shallows of wetlands (cienegas and stock tanks), and stream pool or backwater habitats," the Fish & Wildlife Service wrote.

"The smaller (up to 34-inch-long), narrow-headed garter snake is the most aquatic of the southwestern garter snakes," the agency's news release continued. "(It) is found primarily in clear, rocky, higher-elevation streams along the Mogollon Rim from northern and eastern Arizona into southwestern New Mexico."