Rio Grande Cutthroat Trout Now Endangered Species Candidate

After a review of this native fish's situation, the Service is recommending that the subspecies be formally proposed for protection under the Endangered Species Act.

But the agency will not provide federal safeguards at this time. Instead, the trout has been added to the list of candidate species for protection under the Act. It is number 281 on the candidate list.

"As funding and workloads permit," the Service says its biologists will prepare a proposal for public review that advises listing the trout as either threatened or endangered.

The recommendation follows a 1998 petition and three lawsuits brought by the nonprofit Center for Biological Diversity, based in Tucson, Arizona.

"After 10 years, we are glad the U.S. Fish and Wildlife Service has finally recognized the precarious status of the Rio Grande cutthroat trout," said Noah Greenwald, science director with the Center for Biological Diversity. "Continued delay of protection for the trout, however, is a recipe for extinction."

Rio Grande cutthroat trout face many threats to their survival as a subspecies. (Photo courtesy U.S. Fish and Wildlife Service)

Rio Grande cutthroat trout populations are threatened by nonnative trout, disease, habitat degradation, and climate change.

The Rio Grande cutthroat trout occupies the southern-most habitat of all the cutthroat trout, and the Service acknowledged today that the cold, high elevation streams preferred by this subspecies make it vulnerable to global warming.

"The threats it faces are exacerbated by the effects of climate change," the Service said.

While the extent to which climate change will affect the trout's cold water habitat is not fully understood, the Service said, but warmer water temperatures, decreased stream flow, and a change in the timing of runoff could, singly, or in combination, have a negative effect on the subspecies.

The Rio Grande cutthroat trout is one of 14 subspecies of cutthroat trout and is found in high elevation streams in the Rio Grande, Pecos and the Canadian river basins in New Mexico and Colorado. The species currently occupies a little less than 10 percent of its historical habitat in Colorado and a little more than 10 percent in New Mexico.

The Service found several changes had occurred to Rio Grande cutthroat trout populations since its last review in 2002. In 2002, there were 13 core populations of the Rio Grande cutthroat trout considered sufficiently secure so that federal protection was not considered necessary. This latest review shows only five core populations still meet that definition.

Of the 120 "conservation populations" of Rio Grande cutthroat trout range-wide, 112 exist as isolated fragments with no genetic mixing between populations. The majority of populations, 71 percent, are in short stream segments of five miles or less, which support a limited number of fish.

Although barriers protect most Rio Grande cutthroat trout populations from downstream populations of nonnative trout, 38 percent of Rio Grande cutthroat trout conservation populations share habitat with nonnative trout.

Brook trout and brown trout compete with Rio Grande cutthroat trout for food and habitat. Rainbow trout and other subspecies of cutthroat trout hybridize with Rio Grande cutthroat trout, altering their genetic composition.

Historically, the Rio Grande cutthroat trout was found in rivers at elevations between 7,500 and 8,000 feet. Most Rio Grande cutthroat trout populations today are in elevations between 8,250 to 10,750 feet.

Streams at this elevation are small, subject to drying and freezing, have few deep pools and no options for migration. In addition, an increased occurrence of extreme events such as fire, drought and floods could also impact the remaining populations.

"While we may be able to predict general impacts at this time, we cannot know with precision how the species will be affected," said Benjamin Tuggle, PhD, regional director for the Service. "In light of this uncertainty, we are working with partners to monitor species and habitats to increase our knowledge of specific impacts."

As a candidate species, the Rio Grande cutthroat trout receives no statutory protection under the Endangered Species Act, but its inclusion on the candidate list promotes cooperative conservation efforts.

For example, the Service provides technical assistance and competitive matching grants to states, private landowners, tribes and pueblos undertaking conservation efforts on behalf of candidate species.

The Service also works with landowners to develop Candidate Conservation Agreements. These voluntary agreements allow people to manage their property in ways that benefit candidate species.

The Service uses five factors to determine if a species merits Endangered Species Act protection. If the species meets one of the factors it is eligible for inclusion on the list of threatened and endangered species.

The factors are: the present or threatened destruction, modification, or curtailment of its habitat or range; overutilization for commercial, recreational, scientific, or educational purposes; disease or predation; the inadequacy of existing regulatory mechanisms; or other natural or manmade factors affecting its continued existence.

Greenwald points out that the Rio Grande cutthroat trout will become the nation's 281st candidate species. "On average, the 280 species already on the candidate list have been waiting for protection for 19 years," he said. "Such delays have had real consequences, with at least 24 species having gone extinct after being designated candidates for protection."

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