Prairie Stream/Watershed Ecosystems and Species
 

Wyoming’s grassland ecosystems contain >170 fifth order watersheds (Hydrologic Unit Code [HUCs]), which are drained by >6,700 miles of stream channels. These watersheds also include countless other aquatic habitats including wetlands, springs, potholes and playas. At least 20 sensitive fish and amphibian species depend on these habitats (Table 1).

Table 1. - Prairie Aquatic Ecosystem Species of Greatest Conservation Need in Wyoming

Common Name	Scientific Name	Native Species Status
Black bullhead	Ameiurus melas	NSS3
Common shiner	Luxilus cornutus	NSS3
Finescale dace	Phoxinus neogaeus	NSS1
Flathead chub	Platygobio gracilis	NSS3
Goldeye	Hiodon alosoides	NSS2
Horneyhead chub	Nocomis biguttatus	NSS1
Lake chub	Couesius plumbeus	NSS3
Mountain sucker	Catostomus platyrhynchus	NSS3
Northern Pearl dace	Margariscus margarita	NSS1
Orangethroat darter	Etheostoma spectabile	NSS2
Plains minnow	Hybognathus placitus	NSS3
Plains topminnow	Fundulus sciadicus	NSS2
Sauger	Sander canadensis	NSS2
Shovelnose sturgeon	Scaphirhynchus platorynchus	NSS2
Sturgeon chub	Macrhybopsis gelida	NSS1
Suckermouth minnow	Phenacobius mirabilis	NSS1
Western silvery minnow	Hybognathus argyritis	NSS1
Great Plains toad	Bufo cognatus	NSS4
Plains spadefoot	Spea bombifrons	NSS4
Woodhouse toad	Bufo woodhousei	NSS4

Aquatic habitats are affected by agricultural conversions, invasive and exotic species, interruption of natural vegetation cycles and flow regimes, urbanization, and energy development. The quality of these habitats is directly influenced by any and all actions within a watershed that a stream channel drains. For example, fire suppression has allowed a shift in the vegetative community types present in the system. This shift impacts the hydrologic cycle by shifting the natural flow regime patterns and changing water quality. Due to this undeniable connection, the WGFD manages aquatic habitats from a watershed perspective with a primary goal of maintaining or enhancing overall watershed health. In an attempt to enhance or maintain healthy aquatic habitats, we enhance upland, riparian, and in-channel habitat.

Considerable changes in prairie stream systems have occurred throughout the Great Plains with human settlement and development of the region. The distributions of >50% of the native fish species in prairie streams have been reduced over the previous 30-year period (Patton et al. 1998). Irrigation diversions, reservoir development, and groundwater extraction have altered natural flow regimes and stream channels (Cross and Moss 1987). Historically, large streams had wide, shallow, braided channels with shifting sand beds, turbid water, and little riparian vegetation. By the late 1800s, water development had drastically modified flow regimes and stream channels. Increased riparian vegetation due to increased baseflows by irrigation developments stabilized the once shifting sand bars and changed rivers into single narrow sinuous channels (Fausch and Bestgen 1997).

Alterations have also occurred in transitional streams located between the Rocky Mountains and the large rivers of the Great Plains (Fausch and Bestgen 1997). Water clarity has decreased, and cobble-gravel substrates have been covered by silt and organic material due to runoff from nearby croplands. Irrigation practices have altered flow regimes by dewatering stream sections and enhancing others by return flows (Rahel and Hubert 1991).

Water and land management practices have likely led to species declines by creating barriers to fish movements. Habitat fragmentation by diversion dams, reservoirs, and dewatered stream reaches can impede upstream dispersal of adults and juveniles and interrupt downstream transport of eggs and larvae (Fausch and Bestgen 1997).Shovelnose sturgeon (Scaphirhynchus platorynchus), goldeye (Hiodon alosoides), and sturgeon chub (Macrhybopsis gelida) no longer occur in the North Platte River in Wyoming, probably due to changes in stream temperatures, flow regimes, and turbidity caused by the construction of mainstem reservoirs (Baxter and Simon 1970).

Species introductions have also occurred throughout stream systems of the Great Plains. Most introductions in the MRD have been sport and forage fishes into impoundments (Cross et al. 1986). Due to the fluctuating nature of and harsh conditions in prairie streams, most sport fish introductions into lotic environments have failed. While introductions have increased diversity in prairie streams, it is possible that predation has decreased native species populations (Rabeni 1996).

The most significant immediate threat to native aquatic species in grassland watersheds is energy development, particularly coalbed natural gas (CBNG) activities. The potential exists (and has already begun) for CBNG activities to significantly alter the flow regime and natural water quality in impacted watersheds. For example, the Powder River Basin is one of the last free-flowing prairie stream ecosystems left in the United States, and it still supports an intact native aquatic community. Fish species of greatest conservation need inhabiting the Powder include sauger (Sander canadensis), shovelnose sturgeon, goldeye, plains minnow (Hybognathus placitus), flathead chub (Platygobio gracilis), sturgeon chub and western silvery minnow (Hybognathus argyritis).

The sturgeon chub was petitioned for listing under the Endangered Species Act in 2000. On April 18, 2001, the U.S. Fish and Wildlife Service determined that the listing was not warranted, due to the sturgeon chub being more abundant and better distributed throughout its range than previously believed. Although the determination was not warranted in 2001, changes in water quality or quantity and degradation of habitat could result in the sturgeon chub being petitioned again, or in other species of concern being petitioned for listing.

Native fauna in the Powder River drainage have evolved and adapted to a very dynamic hydrograph with high sediment loads. Changes in this flow regime (i.e. perennial flows) may seriously impact native fauna by altering their use of historical habitats for spawning, rearing, and reproduction. Alterations of channel morphology affect the aquatic biota due to changes in sediment loads, loss of habitat, and possible disruption of migration movements due to barriers created by culverts and/or head cuts. The proposed discharges present risks for serious negative impacts on the Powder River system, including biota and stream channel characteristics.

Literature Cited

Baxter, G. T., and J. R. Simon. 1970. Wyoming Fishes. Wyoming Game and Fish Department Bulletin Number 4. Cheyenne, Wyoming.

Cross, F. B., R. L. Mayden, and J. D. Stewart. 1986. Fishes in the western Mississippi drainage. Pages 363-412 in C. H. Hocutt and E. O. Wiley, editors. The zoogeography of North American freshwater fishes. John Wiley and Sons, New York.

Cross, F. B., and R. E. Moss. 1987. Historic changes in fish communities and aquatic habitats in plains streams of Kansas. Pages 155-165 in W.J. Matthews and D.C. Heins, editors. Community and evolutionary ecology of North American stream fishes. University of Oklahoma Press, Norman, Oklahoma.

Fausch, K. D., and K. R. Bestgen. 1997. Ecology of fishes indigenous to the central and southwestern Great Plains. Pages 131-166 in F. L. Knopf and F. B. Samson, editors. Ecology and conservation of Great Plains vertebrates. Springer-Verlag, New York.

Patton, T. M., F. J. Rahel, and W. A. Hubert. 1998. Using historical data to assess changes in Wyoming’s fish fauna. Conservation Biology 12:1120-1128.

Rabeni, C. F. 1996. Prairie legacies – fish and aquatic resources. In F. B. Samson, F. L. Knopf, editors. Prairie Conservation: preserving North America’s most endangered ecosystem. Island Press, Covelo, California.

Rahel, F. J., and W. A. Hubert. 1991. Fish assemblages and habitat gradients in a Rocky Mountain-Great Plains stream: biotic zonation and additive patterns of community change. Transactions of the American Fisheries Society 120:319-332.