Inventory of Fishes and Aquatic Habitat within the Powder River Basin, Wyoming

In the mid-1990s, the Wyoming Game and Fish Department (WGFD) funded a Ph.D. project through the University of Wyoming to describe the status of fishes in the Missouri River drainage in Wyoming. That dissertation was completed by Tim Patton in 1997. Tim developed a method to prioritize conservation areas based on the value of the fish community in streams throughout eastern Wyoming. The Powder River was ranked in the top ten when he prioritized all streams in the Missouri River based on conservation value.

A few years ago, the Powder River watershed became the focus of a massive, burgeoning, coalbed methane (CBM) industry. Thousands of CBM wells are now being drilled each year – there are already approximately 19,000 in the watershed. It is estimated that this development will result in 50,000-60,000 wells by the time it is over. Coalbed methane wells produce groundwater that is discharged on to the surface of the land. This “product water” has the potential to negatively impact aquatic habitat and fish communities in streams and rivers. The rapid pace of CBM development in the Powder River drainage caused the conservation group American Rivers to designate the Powder River as one of the top ten most endangered rivers in the country in 2001 and 2002. When the WGFD realized that CBM development might impact aquatic wildlife in the watershed, the Aquatic Assessment Crew and Sheridan Regional Fisheries Management Crew started a multi-year project in the drainage.

The goal of this project is to describe the aquatic habitat and the distribution of fishes in the mainstem Powder River and tributaries.

Specific project objectives are to 1) describe the fish community throughout the study area and monitor shifts in the community between locations and over time, 2) describe aquatic habitat throughout the study area and monitor changes, 3) describe habitat use by individual fish species in the study area, and 4) describe seasonal movements of shovelnose sturgeon in Wyoming waters. This detailed information is going to be essential in order to effectively manage this fishery.

The Powder River Basin is the 4^th largest watershed in Wyoming. The three forks of the Powder River converge near Kaycee on Interstate-25 and the river flows east until a short distance after it’s first major tributary, Salt Creek, enters the river. After that, it turns north and flows under I-25 and on into MT. Only about half of the watershed is in Wyoming – the river enters the Yellowstone River about 30 miles east of Miles City, Montana.

The south fork has the largest drainage area of the three upper branches. The only major tributaries in the drainage are Salt Creek, Crazy Woman Creek, and Clear Creek (Figure 1). All of the other washes or creek bottoms that enter the Powder are intermittent, meaning that they flow only when they receive water from snow or rain. Between periods of moisture, they may dry up or be reduced to a series of separate pools.

Figure 1. Location of Powder River watershed and major tributaries in Wyoming.

The Powder River is very unique. It is one of the last remaining remnants of a relatively undisturbed, large prairie river in the United States. It has no major impoundments and the only towns along its length in Wyoming are Kaycee, Sussex and Arvada. It has not been drastically altered by water diversions for agriculture or municipal supplies. It is an extremely turbid (muddy) and seasonally warm stream. You can often see less than an inch into the water and summer water temperatures reach 95 F. The river erodes its way back and forth across a wide floodplain, creating large cottonwood galleries (Figure 2). These large galleries of cottonwoods are disappearing from many rivers in the country that no longer have spring floods due to the construction of dams.

Figure 2. View of the Powder River looking south from Interstate-90. Note large cottonwood galleries on the floodplain.

The river typically flows over 4,000 cubic feet per second (cfs) in spring, but it barely flows or may even become puddled in late summer. It can roar over 10,000 cfs during floods. Flows are very flashy and can rise rapidly after thunderstorms. Many of the small intermittent tributaries flow only in the spring and after thunderstorms. Even Crazy Woman Creek, one of the largest tributaries on the river, often becomes puddled in late summer (Figure 3).

Figure 3. Crazy Woman Creek at low flow.

The Aquatic Assessment Crew and Sheridan Regional Management Crew established eight study sites on the mainstem of the Powder River and two study sites on Crazy Woman Creek in 2004. We added a ninth study site on the mainstem river below Burger Draw in 2005 (Figure 4) (seining). Biologists sampled the fish community at each of these sites using seines (Figure 5) and used the Department’s Warmwater Stream Assessment technique  to describe the habitat that fish were occupying.

Figure 4. Location of Wyoming Game and Fish Department study sites in the Powder River watershed.

Many of fourth and fifth generation ranchers living along the river assume that this often shallow, muddy river is home to a few catfish and suckers, but not much else. However, the mainstem river is actually home to about 20 fish species, most of which are native to the system.

In 2004, more than 63,000 fish were sampled at 8 sites on the Powder River. Only three or four of the species collected are not native to the system (“exotic species”). Three species are definitely not native, but there is still some uncertainty about plains killifish. If we assume that plains killifish are exotic, about 95% of the total number of fish we sampled were native species.

Of the 20 species we collected in the Powder River, seven were given a Native Species Status of one, two or three under the WGFD Mitigation Policy, which designates that these species require additional management consideration to prevent population declines. These species are shown in shaded rows in Table 1. These seven species along with the stonecat, river carpsucker and shorthead redhorse are included as species of concern in the Department’s Comprehensive Wildlife Conservation Strategy.

Table 1. Fish species and numbers captured during 5 sample periods (June-October) at sites on the Powder River and Crazy Woman Creek in 2004.

¹Sauger are found in Clear Creek, a tributary to the Powder River, but have not yet been captured in the Powder River during our sampling. They may migrate from the Powder River in Montana into Clear Creek to spawn.

Figure 5. Seining the Powder River above Crazy Woman Creek.

Native fishes of the Powder River have evolved unique adaptations and life histories. Some species can withstand the periods of no flow, taking refuge in very warm, isolated pools until the river flows again. Some have external taste buds on the head, body and/or fins which help them find food in the low-visibility conditions. Others have specially adapted eyes for seeing in the murky water.

A few of the species like the plains minnow and flathead chub are still quite common in the Powder River, but have largely disappeared from other portions of their native range where habitats have been altered by dams. Other species, like the shovelnose sturgeon, may only migrate into Wyoming waters of the Powder River to spawn. We have not yet captured a shovelnose sturgeon during two years of sampling using seines, but we experimented with floating trammel nets to sample portions of the river in June 2005 and captured 18 shovelnose sturgeon (Figure 6). Most of the fish were captured within a relatively small reach of river, which leads us to assume that these fish had congregated to spawn. Biologists actually know very little about many of the species, which makes it very difficult to answer questions about how CBM water might impact native fish populations.

Figure 6. Small shovelnose sturgeon captured in a trammel net in the Powder River in June 2005.

There are three primary threats to this ecosystem that we will have to manage in the coming years: 1) habitat alterations due to water produced during coalbed methane development, 2) water development in the headwaters of the watershed, and 3) exotic species of fish and plants. Even relatively small amounts of CBM water have the potential to alter the habitat in the Powder River, particularly during periods of low flow. We do not know how these changes might impact native fishes. The construction of reservoirs in the headwaters could change water turbidity, water temperatures, and flow regimes. These changes could negatively impact native species and benefit exotics. Tamarisk (salt cedar) and Russian olive are exotic plants that are abundant along streambanks in some portions of the river. Prolifieration of these species will alter the native riparian plant community, which could also impact the native fish community. Changes in water quality or quantity associated with CBM water and/or the construction of reservoirs could also result in the proliferation of exotic species that are now rare in the river.

We plan to continue surveying the fish community in the Powder River and to work with other agencies like the Department of Environmental Quality, Bureau of Land Management, and the U.S. Geological Survey to develop a detailed, long-term monitoring plan for aquatic wildlife in the drainage. We will also work with these agencies to pursue alternative sources of funding to pay for this monitoring.

It will take a long time to develop an understanding of the fish community in the Powder River. We know so little about many of the native fish species, that it is very risky to hypothesize about how gas and water development will impact them. Our best alternative at this point is to avoid impacts whenever possible, until we can gather the information necessary to accurately assess potential impacts to this unique resource.