The U.S. Fish and Wildlife Service has determined that threatened species status under the Endangered Species Act (ESA) is warranted for the northern Mexican gartersnake (Thamnophis eques megalops) and the narrow-headed gartersnake (Thamnophis rufipunctatus), native species in Arizona and New Mexico. Both species will be listed as threatened throughout their range. Under the ESA, a “threatened” listing means the species is likely to become in danger of extinction within the foreseeable future; this status is a step below “endangered” and allows for more flexibility in how the Act’s protections are implemented. This rule becomes effective August 7, 2014. This final listing rule includes a special rule under section 4(d) of the ESA that will exempt operation and maintenance of livestock tanks on private, state and tribal lands from the prohibitions on “take” of listed species. Some northern Mexican gartersnakes occupy stock tanks, or impoundments maintained by cattlemen as livestock watering holes.
The special rule will allow landowners to construct new stock tanks and to continue to use and maintain those stock tanks on non-federal lands, which may be occupied by northern Mexican gartersnakes, without the need for further regulation. The northern Mexican gartersnake is found in Greenlee, Graham, Apache, La Paz, Mohave, Yavapai, Navajo, Gila, Coconino, Cochise, Santa Cruz, Pima and Pinal counties in Arizona, as well as in Grant and Catron counties in New Mexico. The narrow-headed gartersnake is found in Greenlee, Graham, Apache, Yavapai, Navajo, Gila, and Coconino counties in Arizona, as well as in Grant, Hidalgo, Sierra, and Catron counties in New Mexico.
The northern Mexican gartersnake is also found in the Mexican states of Sonora, Chihuahua, Durango, Coahuila, Zacatecas, Guanajuato, Nayarit, Hidalgo, Jalisco, San Luis Potosí, Aguascalientes, Tlaxacala, Puebla, México, Veracruz and Querétaro. U.S. Fish and Wildlife Service News Release Public Affairs Office PO Box 1306 Albuquerque, NM 87103 505/248-6911 505/248-6915 (Fax)
Northern Mexican and narrow-headed gartersnakes are non-venomous snakes that use riparian and aquatic habitat in Arizona and New Mexico. Both species depend on robust prey bases consisting of native fish and amphibians (narrow-headed gartersnakes only eat fish). Eighty-three percent of northern Mexican gartersnake populations in the U.S. and 76 percent of all narrow-headed gartersnake populations are likely not viable and may exist at low population densities that could be threatened with extirpation or may already be extirpated. Ecological data derived from native fish field research in Mexico suggest that similar trends in northern Mexican gartersnake populations have likely occurred in that country. Northern Mexican gartersnake and narrow-headed gartersnake populations have declined primarily from interactions with harmful nonnative species such as bullfrogs; crayfish; warm-water, predatory sportfish; and brown trout.
These harmful nonnative species prey upon, or compete with the gartersnakes and the native prey species (including native amphibians and fish) that are vital to their existence. Human activities and large-scale wildfires that diminish surface water or degrade streamside vegetation are also significant threats, but particularly where they co-occur in the presence of nonnative species. Therefore, based on the best available scientific and commercial information, the Service has concluded that harmful nonnative species are the most significant threat to both the northern Mexican and narrow-headed gartersnake, range wide. The Service expects the impacts from harmful nonnative species to increase in the foreseeable future. The effects of these threats on both gartersnakes have resulted in the extirpation of a few populations and the decline in abundance in the vast majority of populations. The Service anticipates that the continuing decline of the gartersnakes, in terms of additional population losses and increased risk of extinction in the foreseeable future, will occur over the next several decades.
The Service will finalize the designation of critical habitat for the northern Mexican gartersnake and narrow-headed gartersnake in a separate rule in the future. The northern Mexican gartersnake 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. Within the United States, the most viable populations of northern Mexican gartersnake are found in the middle/upper Verde River drainage, middle/lower Tonto Creek, the San Rafael Valley, the Bill Williams River and a few isolated wetland habitats and stream reaches in southeastern Arizona. The smaller (up to 34-inches), narrow-headed gartersnake is the most aquatic of the southwestern gartersnakes and is a highly specialized predator on native fish species and trout found primarily in clear, rocky, higher-elevation streams along the Mogollon Rim from northern and eastern Arizona into southwestern New Mexico. The U.S. Fish and Wildlife Service works with others to conserve, protect, and enhance fish, wildlife, plants, and their habitats for the continuing benefit of the American people. For more information, visit www.fws.gov, or connect with us through any of these social media channels: