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<br />~J <br />C' <br />1-4 <br /> <br />gg Speckled Dace <br />00 Speckled dace, typically considered to be a riffle-dwelling species, was abundant in the San Juan River. <br />Speckled dace is a small minnow and, therefore, is not as susceptible to collection by electro fishing as the <br />two abundant native sucker species. Even with that caveat, speckled dace was the fifth most-common <br />species collected in mainstream electmfishing sUlVeys (Ryden 2000a). Most other San Juan River main <br />channel sampling did not include riffle habitat, so few data are available on overall speckled dace <br />abundance. Speckled dace was the second or third most-common species collected during sunnner and <br />late sunnner seining sUlVeys in secondary channels (Propst and Hobbes 2000). This species likely spawns <br />in riffle gravel areas in the San Juan River, although spawning was not noted in SJRIP studies. Like <br />bluehead sucker, key habitats for this species are cobble and gravel riffles and similar habitats. <br /> <br />Habitat Availability and Distribution <br />Coincident with the initiation of biological studies looking at fish abundance and habitat use, studies of <br />habitat availability and habitat change resulting from the reoperation of Navajo Dam to mimic a natural <br />hydrograph were also initiated. The first study focused on backwater habitat, a key habitat for YOY <br />Colorado pikeminnow, and investigated the relationship between flow and backwater area using aerial <br />videography (Pucherelli and Goettlicher 1992). Backwater habitat was most abundant at either high flows <br />or low flows. Initiated in 1992, habitat mapping studies used aerial videography and on-the-ground <br />mapping at various flow levels (Bliesner and Lamarra 2000). From 1992 through 1997, 13 habitat- <br />mapping sUlVeys were made at several flows during different seasons. Habitats were classified into 36 <br />types, and these individual types were placed in eight general categories for data sunnnarization and analysis <br />(Table 3.2). Key habitats for the endangered and other native fishes were generally in the low-velocity <br />(adult Colorado pikeminnow, razorback sucker, and roundtail chub), riffle (spawning adult Colorado <br />pikeminnow and razorback sucker and adult bluehead sucker and speckled dace), and backwater and <br />slackwater (YOY Colorado pikeminnow and all other species) categories. <br /> <br />Figure 3.5 shows habitat area, and Figure 3.6 shows habitat as a percentage of total wetted area (TW A) <br />for the eight general categories of habitats at high- (>7,000 cfs), mediwn- (3,000 cfs), and low-flow (<700 <br />cfs) levels for data averaged over the study period. Run habitat was the most-common type in the San Juan <br />River, comprising 80% or more of TW A throughout the study area at all flow levels. Run habitat also <br />increased as flows increased, both in total area (Figure 3.5) and percentage (Figure 3.6). All other habitats <br />combined comprised from about 16% to 20% of the total habitat area. Backwaters and low-velocity <br />habitats, including many of the key habitats for both adult and young native fishes and the two endangered <br />species, comprised less than 2% of the total habitat area, except during low flow when they comprised <br />about 2.5%. Osmundson et al. (1995) mapped habitats at various flows in the 15-mile reach of the <br />Colorado River and found that runs comprised about 60% of the habitat at most flows, followed by riffles <br />at about 25%. Backwaters, eddies, and pools comprised about 5 to 10% of the total swface area at low <br />and moderate flows, much higher amounts than seen in the San Juan River. <br /> <br />September 2000 <br /> <br />3-16 <br /> <br />Program Evaluation Report <br />