7035 - Laserfiche WebLink

Home Browse Search

506 TRANS. AM. FISH. SOC., 1976, NO. 4 TABLE 4.-Mean number of fish collected per 30.5 m of stream in 1964-fj8, 1974, and 1975. Native species denoted with an asterisk (*). 1964--68 data from Deacon and Bradley (1972). HeadwatCf" stations 1 2 3 74 75 64-68 74 7564-68 74 75 Gila robuata" 0 0 3 2 0 11 1 7 Rhinichthys osculus* 0 0 0 0 0 35 23 38 Moapa coriacea" 5 24 42 3 11 36 3 3 Crenichthys baileyi" 28 290 2 2 1 1 1 1 Cyprinus carpio 0 0 0 0 0 3 1 0 Gambusia affinis 32 76 20 13 17 25 55 2 Poecilia mexicana 10 98 85 140 144 136 90 73 Middle river atations 4 5 6 7 - 75 7564-68 74 75 64-68 74 75 Gila robusta" 7 4 21 3 16 8 2 4 Rhinichthys osculus" 26 22 5 3 0 1 1 1 Cyprinus carpio 3 0 2 6 3 0 0 N otrcrpis lutrensis 0 0 0 0 3 0 0 letalurns melas 0 0 1 1 2 0 0 0 Gambusia affinis 4 1 14 8 2 83 2 10 Poecilia mexicana 26 21 28 68 78 59 30 16 Lower river stations 9 10 64-68 74 75 64-68 74 Gila robusta" 1 0 0 0 0 0 Salmo gairdneri 0 0 0 0 1 0 Cllprinus carpio 5 0 4 12 4 11 N otropis lutrensis 43 1 29 75 14 265 Notemigonus cTlIsoleucas 0 0 4 0 1 0 1 etalurns melas 4 0 2 1 0 12 Gambusia affini. 4 2 47 0 0 2 M icrcrpterus salmoides 1 0 0 1 1 6 Chaenobryttus cllanellus 36 0 2 2 13 5 when disturbed, C. baileyi darted into the dense vegetation along the margins of the channel while the other headwater species remained near the surface (P. rnexicana and G. affinis) or in the flowing water (Moapa coriacea). Prior to 1975 a portion of the C. baileyi population may have eluded capture by this behavioral mechanism thus being underrepresented in the samples. C. baileyi declined rapidly in abundance below the springs and was only incidentally present at Stations 2 and 3. Moapa coriacea, present at all headwater stations, exhibited a sharp decline in abun- dance at Stations 2 and 3 since 1964-68. Gila robusta and Rhinichthys osculus did not appear to have changed in abundance. The introduced P. mexicana was the most numer- ous species collected at Stations 2 and 3. 8 75 Fauna of the Middle River Only two native species, R. osculus and G. robusta, occurred in this reach of the river (Table 4). R. osculus was most abundant at Stations 4 and 5 in shallow, cobble riffles and absent from deeper areas over sand and mud substrates. G. robusta was fairly evenly dis- tributed throughout the middle river; no specific habitat preferences were apparent although the roundtail chub probably avoids shallow riffles as does its close relative G. r. seminuda in the nearby Virgin River (Cross 1975). P. mexicana was the numerically dom- inant species in this reach. Physical and chemical alterations of the Moapa River (channelization, streamside vegetation removal, dumping of garbage and organic wastes) were readily apparent below Station 5. Their cumulative effects likely account for the reduction in the number of species collected at Stations 7 and 8 ( Table 4) . 10 o o o o o 6 75 Fauna of the Lower River Native fishes were absent from collections at Stations 9 and 10. Eight nonnative species were collected in the lower river (Table 4). Noternigonus crysoleucas and Salrno gairdneri were incidental to the remaining fauna. The golden shiner may have escaped from a bait- fish farm near Bowman Reservoir. The rain- bow trout (one ripe male caught in January 1974) likely entered the river from Lake Mead seeking a place to spawn. The large number of Notropis lutrensis collected in August 1975 at Station 10 probably resulted from move- ment into the lower river from Lake Mead; summertime movement of the red shiner (as well as carp, largemouth black bass, and green sunfish) into the lower Virgin River has also been observed (Cross 1975). The absence of the native faima from the lower river may be a result of; turbidity, a silt bottom, the presence of nOlln'llve fishes, an increased incidence of parasi(i (Deacon ""fi;",~",:,~~,,,;,,,,,,,,,,:,,