Northern Prairie Wildlife Research Center
Prior surveys of fishes of the mainstem Moreau River are limited to two samples collected with a seine on August 24, 1952 where highways 63 and 65 cross the middle portion of the river on the Cheyenne River Sioux Reservation (Bailey and Allum 1962). The first of these sites is about 40 km downstream from our study area. We found all of the species that were recorded in 1952 in the mainstem of the river except yellow perch (Perca flavescens). The yellow perch is not native to western South Dakota rivers, and the Moreau River record of Bailey and Allum (1962) was their only record of yellow perch in western tributaries to the Missouri River. Even though it has been widely stocked in lakes, it was not found recently in the Cheyenne, White, and Grand rivers and is rare in the Bad and Belle Fourche rivers (Berry, unpubl. data). Based on the scanty historical data, we tentatively concluded that the Moreau River fish community has been persistent over the years since Bailey and Allum's (1962) study in the late 1950's. Ecological persistence is the continued existence of species over time in an area that encompasses the home range of the organism throughout its life cycle (Connell and Sousa 1983).
The historic fish community has probably persisted because of the relatively natural condition of the watershed and lack of impoundments on the main river. In other rivers, impoundments have lowered turbidity, altered stream flow, and provided lentic habitat for centrarchids and white bass. These changes are sometimes harmful to native species (Reigh and Owen 1979, Cross and Moss 1987, Sanders et al. 1993, Wenke et al. 1993). Native species such as flathead chub, plains minnow, western silvery minnow, and longnose dace that are somewhat sensitive to environmental degradation (DEQ 1991) were abundant and widespread in the upper Moreau River Basin. We found a few nonnative fish e.g. largemouth bass, white bass, and bluegill that may have immigrated from small impoundments on tributaries or from Lake Oahe. The immigration may have been facilitated by high spring flows in 1995 and 1996.
Water quality has been judged to marginally support the fish community because of high levels of suspended or dissolved solids, and occasional high levels of fecal coliforms (DENR 1994). We agree that naturally erosive soils are probably the largest contributor of suspended solids (USDA 1980, DENR 1994), because we found only minor livestock use of the riparian zones. Bailey and Allum (1962) made only qualitative observations of habitat at their two sample sites, and recorded that bulrushes were present, the substrate was primarily gravel, sand, and silt, the water was turbid, and the current was swift. Their description matches ours. Our quantitative physical data will be useful in determining future trends in riverine habitat condition. For example, symptoms of overgrazing are accumulation of fine sediment, channel widening and shallowing, decreased water clarity, and bank slumping (Waters 1995). Change in the landscape can cause changes in stream hydrology that affect channel shape over time (Gregory and Madew 1982). For example, channel incision, i.e., the degree to which a river is entrenched into the landscape relative to its width, is often associated with hydrologically degraded systems.
The ichthyofauna of the Moreau River System is similar to that in the Grand and Cheyenne rivers, which are adjacent western tributaries to the Missouri River. The Grand River is similar to the Moreau River in mean daily discharge (0.018 m³/s) and drainage area ( 13,962 km²), and the Grand River has the same fish species that we found in the Moreau River, plus the sturgeon chub (Macrhybopsis gelida) and pumpkinseed (Lepomis gibbosus) (Bailey and Allum 1962, Reigh and Owen 1979). The nonnative pumpkinseed is rarely found in western rivers, but the sturgeon chub may exist in portions of the Moreau River that we did not sample (Ziebach and Dewey counties). The sturgeon chub is considered widespread but not common in the Cheyenne and White rivers (Hampton and Berry 1997, Berry, unpubl. data). The Cheyenne River is larger (mean daily discharge 0.06 m³/s) than the Moreau River. Its ichthyofauna comprises 30 species, including all of those found in the Moreau River (Hampton and Berry 1997).
Data concerning the fish fauna of historical interest were gathered in 1879 by naturalist E. D. Cope, who made zoological notes as he traveled into the Dakota Territory in search of fossils (Cope 1879). Cope visited Battle Creek (perhaps today called Blue Blanket Creek), which he described as emptying into the west side of the Missouri River not far north of the mouth of the Moreau River. Cope (1879) found longnose dace, western silvery minnow, fathead minnow, burbot, channel catfish, creek chub, and two daces of uncertain identity. We found all of the identified species in the Moreau River.
Although the Moreau River fish species persisted between 1952 and 1997, the populations were probably unstable, as has been found for other streams (e.g., Strange et al. 1992) and which has been predicted for intermittent runoff streams such as the Moreau River (Poff and Ward 1989). We cannot evaluate population trends without historical data on fish density, but future workers will be able to use our data to estimate temporal changes in the size and health of some populations. For example, simple length-frequency data show that recruitment does not occur in some Great Plains streams where over-winter mortality is high (Patton and Hubert 1996). We found many sizes of channel catfish in our samples, which indicated that recruitment was taking place.
Our CPUE data will perhaps be useful for discerning population trends in the future if our methods are repeated, with particular emphasis on sampling similar habitats during similar time periods. Our detailed hydrological and physical data should be useful in designing a future survey that closely duplicates conditions during our survey, thus controlling several sources of variability, which are already rather high. Assessing differences in CPUE over time requires the use of appropriate descriptive statistics and statistical tests because data from low-density populations are not usually normally distributed (Hubert 1996:159). Most (about 66%) of the populations in the Moreau River had seine net CPUE values that were less than 0.1 fish/m.
Channel catfish growth in plains rivers in states such as Wyoming, Iowa, Nebraska, and North Dakota depends on biotic and abiotic factors specific to each river (reviewed by Patton and Hubert 1996). The Wr value reflects characteristics of the environment like habitat quality, water quality, and prey availability (Liao et al. 1995). The Wr values change as fish grow, but the model for riverine populations is not well understood (Brown et al. 1995). The skewed U-shaped Wr pattern that we observed for channel catfish has been found in other riverine populations in South Dakota (Doorenbos et al. 2000), and (with some exceptions) in riverine populations elsewhere. For example, the 32 riverine catfish populations included in the calculation of a standard-weight equation for channel catfish (Brown et al. 1995) had the following mean Wr values by length category: stock to quality, 97; quality to preferred, 91; preferred to memorable, 93; and memorable to trophy, 96 (M. Brown, pers. comm., unpubl. data).
In summary, we added seven species (bluegill, brassy minnow, brook stickleback, creek chub, emerald shiner, Iowa darter, and white bass) to the list of fishes found in the Moreau River. Twenty-six of the 38 species recorded in the Moreau are found in the upper basin. The physical habitat and fish community have probably changed little since the 1950's survey of Bailey and Allum (1962). Our data on physical river features, on the riverine fish community, and on structural indices for some fish populations should provide a well-quantified baseline for river monitoring programs in the future.