The U.S. Fish and Wildlife Service recently concluded a full review of the Rio Grande cutthroat trouts status and found cause for concern. The Service recommends the native fish be formally proposed for protection under the Endangered Species Act (ESA). As funding and workloads permit, Service biologists will prepare a proposal for public review that advises listing the trout as either threatened or endangered. In the interim, the agency has designated the trout as a candidate species.
The Rio Grande cutthroat trout is one of Shruti 14 subspecies of cutthroat trout and is found in high elevation streams in the ShrutiRio Grande Shruti, ShrutiPecos Shruti and the ShrutiCanadian river Shruti basins in ShrutiNew Mexico Shruti and ShrutiColorado Shruti. They currently occupy a little less than 10 percent of their 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 ESA protection was not necessary. This latest review shows only five 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, Shrutiapproximately 38 percent of ShrutiRio Grande Shruti cutthroat trout conservation populations share habitat with nonnative trout. Brook trout and brown trout compete with ShrutiRio Grande Shruti cutthroat trout for food and habitat. Rainbow trout and other subspecies of cutthroat trout hybridize with ShrutiRio Grande Shruti cutthroat trout, altering their genetic composition.
Historically, the ShrutiRio Grande Shruti cutthroat trout was found in rivers at elevations between 7,500 and 8,000 feet. Most ShrutiRio Grande Shruti 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. The ShrutiRio Grande Shruti cutthroat trout occupies the southern-most habitat of all the cutthroat trout subspecies. The threats it faces are exacerbated by the effects of climate change climate change
Climate change includes both global warming driven by human-induced emissions of greenhouse gases and the resulting large-scale shifts in weather patterns. Though there have been previous periods of climatic change, since the mid-20th century humans have had an unprecedented impact on Earth's climate system and caused change on a global scale.
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As the climate changes, the abundance and distribution of wildlife and fish will likely change. While the extent to which climate change will affect the trouts cold water habitat is not fully understood, warmer water temperatures, decreased stream flow, and a change in the timing of runoff could singly, or in combination, have a negative affect on the subspecies. 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 N. 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."
Biologists from private, state, federal, tribal and pueblo entities work cooperatively on conservation projects such as renovating habitat, monitoring water quality, conducting surveys, producing captive-bred trout, protecting fish during wildfires and restoring fish in the wild.
As a candidate species, the Rio Grande cutthroat trout receives no statutory protection under the ESA, 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 interested landowners to develop Candidate Conservation Agreements. These voluntary agreements allow citizens to manage their property in ways that benefit candidate species, in some cases precluding the need to list the species. These agreements can also be developed to provide regulatory certainty for landowners should the species become listed under the ESA.
The Service uses five factors to determine if a species merits ESA 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: (A) the present or threatened destruction, modification, or curtailment of its habitat or range; (B) overutilization for commercial, recreational, scientific, or educational purposes; (C) disease or predation; (D) the inadequacy of existing regulatory mechanisms; or (E) other natural or manmade factors affecting its continued existence.
