One of two species of alpine stonefly federal wildlife managers are adding as a “threatened” species resides in the Teton Range, but it’s at risk of losing its meltwater-fed home here.
It wasn’t until 2015 that entomologists realized that small drainages connected to Delta Lake, Mica Lake, South Cascade Creek and Teton Meadows harbored populations of the western glacier stonefly. The discoveries four years ago slowed an in-the-works Endangered Species Act listing at the time, but last week the U.S. Fish and Wildlife Service published a rule that declared the species, plus another stonefly, as too imperiled, and deserving of the “threatened” classification.
“We have determined that habitat fragmentation and degradation in the form of declining streamflows and increasing water temperatures resulting from climate change are currently affecting habitat for the meltwater lednian stonefly and the western glacier stonefly,” Fish and Wildlife officials wrote in a final rule published Thursday in the Federal Register.
The rule states that “most glaciers” supplying cold water to the stonefly habitats in Glacier National Park are projected to melt by 2030.
“As a result,” the rule says, “habitat with a high probability of occupancy for the meltwater lednian stonefly is modeled to decrease 81 percent by 2030.”
Currently, meltwater lednian stoneflies are known to exist in 113 streams, all but four in Glacier Park and all in northwestern Montana and southwest Alberta, Canda. Within those streams they are far from widespread, living on average only in the 1,942 feet immediately downstream of the source of meltwater.
Although more geographically distributed in the Rockies, the western glacier species has even fewer remaining known haunts. They are known to occur in 16 streams: six in Glacier, four in Grand Teton National Park, and six in the Custer-Gallatin National Forest’s Absaroka/Beartooth Wilderness. Similar to their now-threatened counterpart, western glacier stoneflies are found in short reaches nearest where snow and ice are giving way to water.
When the Fish and Wildlife Service acknowledged the newfound Wyoming habitat in 2017, updating its proposed rule, then-Gov. Matt Mead used the discovery as reason to discourage a listing.
“As a result of this new, best available science, I submit that this species’ range and abundance are much more robust than originally assumed,” Mead wrote to the federal agency at the time. “Based on the vast distance separating these known occurrences, it is reasonable to extrapolate that the species likely occurs in available habitats north of Glacier National Park, south of Grand Teton National Park and in all suitable locations between.”
The effect of the warming climate on glaciers, small icefields, and perennial and seasonal snowpack has already been well documented, and the loss of stonefly habitat is already well underway. Glacier Park has lost 83% of its glaciers larger than 25 acres in size since its establishment in 1910, and those that remain are on track to disappear this century. The Tetons house 11 glaciers, and all of them have retreated since first being surveyed in the late 19th and early 20th centuries.
One alpine habitat that could harbor western glacier stoneflies and other meltwater-dependent species after surface glaciers have disappeared in the Tetons and elsewhere are “icy seeps,” the term for outflows of water that emerge from subterranean glaciers called “rock glaciers,” which are projected to better withstand climate change.
The western glacier stoneflies that hang on in the Tetons are small, about a quarter to a third of an inch long, and don’t tolerate water warmer than 43 degrees Fahrenheit. Their ecological niche is that of composter, breaking down vegetation that deposits in the high streams and seeps.
The process of listing the western glacier and lednian meltwater stoneflies stretched more than a dozen years, stemming from petitions from advocacy groups that later sued.
Protecting both species from losing their meltwater homes will be a tall task. The global problem of climate change, federal wildlife managers determined, is the only true threat.
“Given the remote nature of these species’ alpine habitats and extremely limited human activity in these areas,” the rule says, “we found no other habitat-based threats to either species.”
The western glacier and lednian meltwater stoneflies officially become threatened species Dec. 23.