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<br />Fig. 1. Collection sites in the San Rafael River Basin: (1) San Rafael River, 3 km up-
<br />stream from ifs mouth; (2) San Rafael River, 3.2 km upstream from Rt. 24 bridge; (3) San
<br />Rafael River of San Rafael Campground; (4) San Rafael River, 16 km upstream from 3; (5)
<br />San Rafael River, 2.7 km downstream from mouth of Ferron Creek; (b) Huntington Creek,
<br />19.2 km upstream from its mouth; (7) Cottonwood Creek, 12.8 km upstream from its mouth]
<br />(8) Rock Canyon Creek, 1.6 km upstream from ifs mouth; (9) Ferron Creek, 12.8 km up-
<br />stream from its mouth.
<br />fishes in the San Rafael River, before energy development alters the
<br />fish fauna.
<br />STUDY AREA. The San Rafael Basin encompasses about 4500 km2 in south-
<br />eastern central Lltah (Fig. 1). The river is formed by the confluence of Hwiting-
<br />tou. (:ottuuwoud, and Ferron creeks, nes:r the town of Castle Dt~le (Emery Co.),
<br />Utah. The river then flows about 175 km through the San Rafael Swell of the
<br />grid Colorado Plateau and terminates at the Green River downstream from the
<br />town of Green River, Utah.
<br />The San Rafael River is generally a wide, shallow stream. The bottom is pre-
<br />42
<br />dominately sand or silt, but the upper reaches have extensive areas of rubble and
<br />gravel. Streamside vegetation is sparse: dominant riparian plant species ark '
<br />tamarisk (Tamariz pentandra) and willows (Saliz spp.). '
<br />The average annual precipitation at Castle Dale is near 22 cm (Utah State
<br />Engineer ND). However, it fell to 65% of average during 1977 (Nat. Oceanic`
<br />and Atmos. Admin. 1977). Consequently, streamflows were reduced, especially
<br />in late summer and early fall, when the main river Ilow became. intermittent.
<br />From 1971 to 1977 flows near the mouth of the river ranged from 0.3 to 47.5
<br />mg/s (U.S. Geol. Surv. 1971-75). Except for brief, high intensity storms, stream-
<br />flow is dependent on runoff from the nearby mountains. As is typical of south-
<br />eastern Utah streams, the river below its tributaries carries a high sediment load.
<br />METHODS. Fish were collected from the San Rafael .River and tributaries
<br />in March-April, June, and October 1977 at nine stations (Fig. 1). March-April
<br />collections were made with x230-W backpack electrofishing apparatus. Two pass-
<br />es were made through each 100 m section that was sampled. However, the elec-
<br />trofishing gear was judged to be ineffective because of the high conductivity of
<br />the river; consequently, the June and October collections were made with a 7 m
<br />seine (3 mm mesh). Fish were seined from 50 m sections, and the catch doubled
<br />to represent a 100 m section. Stations were chosen that contained both riffle and
<br />pool habitat. Each station was seined repeatedly until relatively few fish were
<br />collected. Captured fish were held in containers until the sampling was com-
<br />pleted, and were then identified, counted, and returned to the water. Selected
<br />samples were preserved for future reference. Water quality characteristics (tem-
<br />perature, dissolved oxygen, alkalinity, pH, hardness, turbidity, conductivity,
<br />phosphate, and chloride) were determined at each station with a Hach water
<br />quality kit (Model DR-EL). Water velocity was determined at each station with
<br />a March-McBirney velocity meter (Model 201).
<br />RESULTS. Fish distribution.-The speckled dace (Rhinichthys
<br />osculus) was the most common native species in the San Rafael River
<br />and its tributaries (Table 1). It was followed, in order, by the flan-
<br />nelmouth sucker (Catostomus latipinnis), bluehead sucker (C. dis-
<br />cobolus), and roundtail chub (Gila robusta). One young-of-the-year
<br />Colorado squawfish (Ptychocheilus Lucius), an endangered species
<br />(U.S. Dept. Int. 1973), was found at station 1 in October (Fig.
<br />2). The red shiner (Notropis lutrensis) was the most common in-
<br />troduced fish, followed by the fathead minnow (Pimephales prome-
<br />las), black bullhead (Ictalurus melas), and channel catfish (l. punc-
<br />tatus).
<br />In general, native and introduced fish were separated in the river
<br />system. Introduced fish .were found only at the farthest downstream
<br />stations (1 and 2), and native fish only at upstream stations (3-9.
<br />At most stations, diversity and abundance was greater in the June
<br />samples than in the March-April or October samples. Of the more
<br />43
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