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<br />
<br />504
<br />
<br />TRANS. AM. FISH. SOC., 1976, NO.4
<br />
<br />
<br />I SPRING
<br />
<br />KILOMETERS
<br />-----=-
<br />1 0 1 2 3
<br />
<br />FIGURE I.-Moapa River showing location of sampling
<br />stations.
<br />
<br />above Station 9 to Bowman Reservoir. Water
<br />in the stream channel at Station 9 consisted
<br />of effluent from a dairy processing plant and
<br />irrigation leaching (probably accounting for
<br />the fact that only 4 Gambusia affinis and 2
<br />Notropis lutrensis were collected in 30.5 m
<br />of stream);
<br />Deacon and Bradley (1972) divided the
<br />fish fauna of the Moapa River into headwater,
<br />middle, and lower groups as suggested by
<br />their data. For purposes of discussion and
<br />comparison the river and fauna will be sim-
<br />ilarly treated in this paper.
<br />The headwaters of the Moapa River are
<br />represented by Stations 1 (spring source), 2,
<br />and 3 (upper reach of the river) (Fig. 1).
<br />The streams at Station 1 averaged less than
<br />2 m wide and 20 cm deep with a mean current
<br />velocity of 0.45 m/s. Gravel and pebbles
<br />composed the substrate. Vegetation consisted
<br />of Najas, Nasturtium, Eleocharis, Chara, and
<br />
<br />other algae; the heaviest growths of submer.
<br />gent vegetation occurred along channel mar.
<br />gins. Stations 2 and 3 averaged 5 m wide and
<br />35 cm deep. Mean current velocity was O.B
<br />m/s in runs and 0.9 m/s in riffles. Substrates
<br />consisted of cobbles and pebbles with areas of
<br />sand and mud. Streamside vegetation included
<br />Prosopis, Tamarix, Salix, Washingtonia, Alri.
<br />plex, Phragmites, Carex, and Bacharis. A low.
<br />head dam above Station 3 contributed to
<br />cooling of the water at Station 3.
<br />Stations 4 through 8 represent the middle
<br />reach of the Moapa River. Mean width was
<br />4 m and mean depth was 35 cm. Current
<br />velocities ranged from 0.2 m/ s in deeper areas
<br />to 0.8 m/s in shallow riffles. Substrates in.
<br />cluded mud, sand, gravel, and cobbles. Stream,
<br />side vegetation consisted of Prosopis, Tamarix.
<br />Populus, Atriplex, Salix, Carex, Typha, Ph rag-
<br />mites, and Bacharis.
<br />The lower reach of the Moapa River is
<br />represented by Stations 9 and lO. Mean width
<br />was 3.5 m and mean depth was 20 em. Cur'
<br />rent velocities ranged from 0.2 to 0.5 m/s.
<br />The bottom varied from soft mud and sand
<br />to firmer gravel and pebbles. Tamarix, PUTJll'
<br />Ius, Salix, Atriplex, Bacharis, and Phragmitc$
<br />were found along the stream.
<br />
<br />METHODS
<br />
<br />Collections were made from January 8
<br />through January 16, 1974, at seven stations
<br />and from August 8 through August 12, 1975,
<br />at ten stations. Vegetation, substrate, width.
<br />and depth were recorded for each statioll.
<br />Current velocity was measured with a Curley
<br />Current Meter (No. TWlO07); temperature.
<br />pH, specific conductance, and dissolved oxy.
<br />gen were measured with a Hydrolab Surveyor
<br />
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<br />TABLE I.-Dissolved oxygen, conductivity, pH, and temperature Jor the Moapa River (January 1974 abol'~.
<br />August 1975 below).
<br /> Stations
<br /> 2 3 4 5 6 7 8 9 10
<br />Dissolved Ol<)'gen (ppm) 5.8 7.1 7.3 8.9 8.6 6.9 !J.4
<br /> 4.2 5.0 7.5 5.5 6.6 7.1 4.9 6.8 6.1 6.1 ,
<br />Conductivity (I'mhos/cm) 1,000 1,000 1,100 1,400 1,400 2,600 2,100
<br /> 920 1,030 1,100 920 1,150 1,100 1,350 2,800 2,950
<br />pH 7.1 7.4 7.5 8.0 8.4 7,2 8.0
<br /> 7.2 7.6 7.9 7.9 8.1 8.2 7.9 7,9 7.3 7.8
<br />Temperature (C) 30,0 26.0 25.0 18.5 16,0 14,0 14.0 l:.
<br /> 31.0 31.0 31.0 27.5 27.5 25.1 26.0 24.2 24.0 23.:::
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