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The Fishes of the Upper Moreau River Basin

Study Site


The Moreau River Basin (13,096 km²) lies entirely in South Dakota and in the Great Plains Ecoregion within the Northern Plateau and Pierre Shales physiographic regions (Johnson et al. 1995). The 560 km-long river flows through a sparsely populated area (about 1.6 people/km²) with no municipalities. Large livestock ranches manage native grass cover on about 80% of the basin and use the remaining 20% for cropland (USDA 1980). The basin receives 35 to 60 cm of annual precipitation.

Nine streams originating near the Montana-South Dakota border make up the headwaters that form the North and South forks (Fig. 1). The mainstem of the river forms at the confluence of the North and South forks and flows eastward for 400 km, 147 km of which is our mainstem study section in Perkins County. The lower half (253 km) of the river flows through the Cheyenne River Indian Reservation before entering Lake Oahe. Mean daily discharge is 3.9 m³/s (range = 0.0 to 705 m³/s), but discharge fluctuates seasonally from a monthly mean of 0.2 m³/sec in winter to about 11.0 m³ /sec during spring runoff (Fig. 2). Poff and Ward (1989) included the Moreau River in their much-cited hydrologic study because the river has been subject to few alterations; and has not been impounded as have many Great Plains rivers. They classified the Moreau River as an intermittent runoff stream. In this class of stream, flow variability is thought to be the major abiotic control on the fish community.

Figure 2 - Line graph for mean monthly hydrographs

Figure 2.  Mean monthly hydrographs for the Moreau River near Faith, South Dakota for 1943 to present (dashed line labeled historical), for 1995 (dotted line), and for 1996 (solid line) (USGS 1996, 1997).

Three classified uses of the main river are: 1) limited contact recreation throughout, 2) semipermanent warmwater fishery in the mainstem, and 3) marginal warmwater fishery in upper basin tributaries (DENR 1994). Some tributaries are not classified, whereas others are classified for wildlife propagation and stock watering, or for irrigation. Water quality standards that are sometimes exceeded include suspended solids, salinity, total dissolved solids, and chlorides (DENR 1990, 1994). During our study conductivity in the main river ranged from 2000 to 3700 µS/cm, total dissolved solids ranged from 840 to 1750 mg/L, pH ranged from 8.2 to 9.0, and dissolved oxygen ranged from 5.4 to 8.5 mg/l (Table 2).

Table 2.  Moreau River fish sampling station numbers and station length, mean width, mean depth, mean bankfull width, dissolved oxygen, conductivity, total dissolved solids, gradient, and discharge in 1995 and 1996.
Station
Number
Station
Length
m
Year Mean
Width
m ▒ SE
Mean Depth
m ▒ SE
Mean
Bankfull
Width
m ▒ SE
Dissolved
Oxygen
mg/l
Conductivity
ÁS/cm
Gradient
cm/100m
Total
Dissolved
Solids
mg/L
Discharge
m3/s
1 509 1995 12.8 (1.3) 46.0 (6.4) 20.8 (1.6) 7.5 3200 22 1530 0.82
1996 12.6 (1.4) 46.8 (4.4) 15.9 (1.3) 7.3 3500 14 840 0.45
2 468 1995 12.7 (0.9) 58.6 (4.5) 17.5 (0.8) 7.2 3400 4 1680 0.39
1996 12.8 (0.8) 49.7 (3.0) 14.6 (0.7) 7.5 2900 12 1580 0.53
3 458 1995 12.8 (1.1) 54.4 (4.7) 18.5 (1.2) 7.2 2800 5 1400 0.51
1996 13.6 (1.4) 54.4 (5.2) 17.6 (1.1) 8.5 3500 4 1660 1.17
4 574 1995 15.7 (1.5) 45.6 (2.6) 23.4 (1.0) 7.6 2800 24 1430 0.43
1996 17.8 (1.4) 44.7 (3.2) 23.5 (1.0) 7.7 2900 8 1480 0.75
5 360 1995 10.3 (0.6) 48.8 (3.0) 15.4 (1.6) 7.2 2600 4 1600 0.35
1996 14.2 (1.3) 47.0 (2.4) 17.0 (1.4) 6.5 3200 3 1630 1.01
6 536 1995 17.8 (1.9) 49.0 (3.9) 29.8 (2.6) 8.4 2900 16 1470 0.36
1996 20.1 (1.8) 58.3 (4.1) 27.4 (1.9) 6.2 2500 23 1460 0.63
7 500 1995 14.9 (1.8) 32.9 (2.2) 27.8 (2.8) 7.1 3500 10 1720 0.27
1996 17.6 (1.2) 48.8 (3.3) 30.8 (1.9) 5.8 3700 5 1750 0.43
8 594 1995 19.3 (1.5) 51.2 (1.9) 23.1 (1.0) 8.1 2800 2 1410 0.18
1996 19.7 (1.2) 53.4 (2.7) 24.3 (1.0) 8.3 2600 4 1580 0.81
9 576 1995 15,8 (2.2) 38.5 (2.4) 26.1 (1.0) 7.7 3400 10 1730 0.16
1996 17.7 (1.9) 34.5 (6.4) 29.8 (1.1) 5.4 3600 10 1690 0.47
10 570 1995 16.2 (1.2) 30.2 (2.0) 22.3 (0.6) 7.6 2800 13 1430 0.35
1996 20.4 (1.0) 52.0 (3.0) 21.3 (0.9) 6.9 2000 5 1040 3.10
11 486 1995 17.0 (0.6) 52.1 (2.3) 22.0 (0.9) 8.1 2900 8 1390 3.03
1996 19.6 (0.9) 51.6 (2.9) 21.1 (0.8) 6.7 2300 5 1200 3.00

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