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<br />. .. <br /> <br />001621 <br /> <br />Speckled Dace <br />Speckled dace, typically considered to be a riffle-dwelling species, was abundant in the San Juan <br />River. Speckled dace is a small minnow and, therefore, is not as susceptible to collection by <br />electrofishing as the two abundant native sucker species. Even with that caveat, speckled dace was <br />the fifth most-common species collected in mainstream electro fishing surveys (Ryden 2000a). <br />Most other San Juan River main channel sampling did not include riffle habitat, so few data are <br />available on overall speckled dace abundance. Speckled dace was the second or third most- <br />common species collected during summer and late summer seining surveys in secondary channels <br />(Propst and Hobbes 2000). This species likely spawns in riffle gravel areas in the San Juan River, <br />although spawning was not noted in SJRIP studies. Like bluehead sucker, key habitats for this <br />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, <br />studies of habitat availability and habitat change resulting from the reoperation of Navajo Dam to <br />mimic a natural hydrograph were also initiated. The first study focused on backwater habitat, a key <br />habitat for YOY Colorado pikeminnow, and investigated the relationship between flow and <br />backwater area using aerial videography (Pucherelli and Goettlicher 1992). Backwater habitat was <br />most abundant at either high flows or low flows. Initiated in 1992, habitat mapping studies used <br />aerial videography and on-the-ground mapping at various flow levels (Bliesner and Lamarra 2000). <br />From 1992 through 1997, 13 habitat-mapping surveys were made at several flows during different <br />seasons. Habitats were classified into 36 types, and these individual types were placed in eight <br />, general categories for data summarization and analysis (Table 3.2). Key habitats for the <br />endangered and other native fishes were generally in the low-velocity (adult Colorado pikeminnow, <br />razorback sucker, and roundtail chub), riffle (spawning adult Colorado pikeminnow and razorback <br />sucker and adult bluehead sucker and speckled dace), and backwater and slackwater (YOY <br />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 <br />(TW A) for the eight general categories of habitats at high- (>7,000 cfs), medium- (3,000 cfs), and <br />low-flow (<700 cfs) levels for data averaged over the study period. Run habitat was the most- <br />common type in the San Juan River, comprising 80% or more ofTW A throughout the study area <br />at all flow levels. Run habitat also increased as flows increased, both in total area (Figure 3.5) and <br />percentage (Figure 3.6). All other habitats combined comprised from about 16% to 20% of the <br />total habitat area. Backwaters and low-velocity habitats, including many of the key habitats for <br />both adult and young native fishes and the two endangered species, comprised less than 2% ofthe <br />total habitat area, except during low flow when they comprised about 2.5%. Osmundson et al. <br />(1995) mapped habitats at various flows in the IS-mile reach of the Colorado River and found that <br />runs comprised about 60% of the habitat at most flows, followed by riffles at about 25%. <br />Backwaters, eddies, and pools comprised about 5 to 10% of the total surface area at low and <br />moderate flows, much higher amounts than seen in the San Juan River. <br /> <br />3-16 <br /> <br />Program Evaluation Report <br /> <br />September 2000 <br />