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Powder River Yields Rare Aquatic Insects

The Powder River is a vast drainage representing one of the last undammed, large prairie river systems in the United States. In southeastern Montana, it flows through a relatively intact natural landscape with sweeping meanders across the valley bottom, side channels, oxbows, shifting islands and a functional floodplain. The Powder also provides key habitat for several fish Species of Concern, as well as important riparian habitat for many wildlife species that inhabit the prairie landscape. In spite of their ecological importance, prairie rivers have received relatively little study in the past, compared to cold-water streams farther west that support the more popular sport fisheries.

Last summer, MTNHP biological survey efforts focused on the Powder River, with funding from the BLM, to provide better information for resource management and decision-making in this increasingly important area for energy development. Our biologists' work, though by no means comprehensive, was very productive. Some of the biggest discoveries, predictably, focused on the smallest and least-studies critters: aquatic invertebrates.

Surveys by Aquatic Ecologist Dave Stagliano and Biologist Coburn Currier turned up three mayflies of very limited distribution in Montana as well as a dragonfly new to the state. The Brimstone Clubtail (Stylurus intricatus), a bright green dragonfly with black stripes, was found at four sampling sites upstream of Broadus in sandy gravel habitat. Although fairly widespread in central and western North America (G4 rank), this species had never been documented in Montana. (For good images, see www.southwestdragonflies.net.)

Even more exciting, one of the mayflies Dave found was Anepeorus rusticus a sand-dwelling species that is ranked G1, having been reported only from Montana, Saskatchewan and Utah. Two other state-rare mayflies turned up as well: Homoeoneuria alleni (G4, S2), a sand-dwelling species Raptoheptagenia cruentata (G4, S2), a riffle-dweller. (Since mayflies haven't earned the notoriety of dragonflies, they don't yet have common names sorry!). Two other rare sand-dwelling mayflies were also found on the Powder a few years ago by Dan Gustafson (surveying earlier in the season) Analetris eximia (G2G4, S3) and Lachlania saskatchewanensis (G4, S1).

The larger objective of Dave's work is to apply biological assessment measures to evaluate the quality of aquatic biological communities in the Powder and its tributaries. His analysis found the reach upstream of Rough Creek to be most biologically intact (supporting the largest number of species expected for that type of stream habitat), with the reach at the Wyoming border and the Dry Creek drainage also ranking high. If you want to learn more about our aquatic classification and biological integrity measures, check out Dave's report on our website (Aquatic Surveys and Assessment within the Middle Powder River Watershed). A report on the larger survey effort that included other animal groups will be available later this spring.

Our aquatic ecology program has added a critical dimension to MTNHP's survey efforts and will continue to expand our knowledge of Montana's aquatic heritage especially among the invertebrates. Thanks to Dan Gustafson at MSU for help in identification and ranking, and to the BLM for funding these surveys.

Contact: Dave Stagliano
(444-7329)

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