Random versus Fixed-Site Sampling When Monitoring Relative Abundance of Fishes in Headwater Streams of the Upper Colorado River Basin MICHAEL C. QUIST* 1 U.S. Geological Survey, Wyoming Cooperative Fish and Wildlife Research Unit, University of Wyoming, Department 3166, 1000 East University Avenue, Laramie, Wyoming 82071, USA KENNETH G. GEROW Department of Statistics, University of Wyoming, Department 3332, 1000 East University Avenue, Laramie, Wyoming 82071, USA MICHAEL R. BOWER 2 U.S. Bureau of Land Management, Post Office Box 2407, Rawlins, Wyoming 82301, USA WAYNE A. HUBERT U.S. Geological Survey, Wyoming Cooperative Fish and Wildlife Research Unit, University of Wyoming, Department 3166, 1000 East University Avenue, Laramie, Wyoming 82071, USA Abstract.—Native fishes of the upper Colorado River basin (UCRB) have declined in distribution and abundance due to habitat degradation and interactions with nonnative fishes. Consequently, monitoring populations of both native and nonnative fishes is important for conservation of native species. We used data collected from Muddy Creek, Wyoming (2003–2004), to compare sample size estimates using a random and a fixed-site sampling design to monitor changes in catch per unit effort (CPUE) of native bluehead suckers Catostomus discobolus, flannelmouth suckers C. latipinnis, roundtail chub Gila robusta, and speckled dace Rhinichthys osculus, as well as nonnative creek chub Semotilus atroma- culatus and white suckers C. commersonii. When one-pass backpack electrofishing was used, detection of 10% or 25% changes in CPUE (fish/100 m) at 60% statistical power required 50–1,000 randomly sampled reaches among species regardless of sampling design. However, use of a fixed-site sampling design with 25–50 reaches greatly enhanced the ability to detect changes in CPUE. The addition of seining did not appreciably reduce required effort. When detection of 25– 50% changes in CPUE of native and nonnative fishes is acceptable, we recommend establishment of 25–50 fixed reaches sampled by one-pass electrofishing in Muddy Creek. Because Muddy Creek has habitat and fish assemblages characteristic of other headwater streams in the UCRB, our results are likely to apply to many other streams in the basin. Fisheries scientists need information on the occur- rence and abundance of fishes to guide management and conservation efforts. For instance, understanding the distributions of native species may identify large- scale factors influencing their occurrence, populations that warrant study, or stream segments that require protection from deleterious anthropogenic activities (Luttrell et al. 1999; Jackson et al. 2001). Information on the distribution of nonnative fishes can be used to identify areas where management activities (e.g., nonnative fish removal efforts, translocation of native species) should be directed (Kruse et al. 1997; Novinger and Rahel 2003). Similarly, information on the abundance of fishes is critical for assessing populations and their response to management activ- ities or anthropogenic disturbances. Native fishes have declined in distribution and abundance across the upper Colorado River basin (UCRB). Cumulative effects of habitat alterations and interactions with nonnative fishes are cited as the primary mechanisms responsible for declines (Min- ckley and Deacon 1991; Bezzerides and Bestgen 2002; Minckley et al. 2003). In Wyoming, 11 fish species are native to the UCRB (Baxter and Stone 1995). Three of these species are federally endangered species (i.e., razorback sucker Xyrauchen texanus, bonytail Gila elegans, and Colorado pikeminnow Ptychocheilus lucius) and are probably extirpated from Wyoming. The bluehead sucker Catostomus discobolus, flannel- mouth sucker C. latipinnis, and roundtail chub Gila robusta are of particular interest because their distri- butions have been reduced by about 50% across the Colorado River basin (Bezzerides and Bestgen 2002). Only two small watersheds in Wyoming are currently known to contain sympatric populations of these three species, one of which is Muddy Creek (Little Snake * Corresponding author: mcquist@iastate.edu 1 Present address: Department of Natural Resource Ecology and Management, Iowa State University, 339 Science II, Ames, Iowa 50011, USA. 2 Present address: National Park Service, Death Valley National Park, Post Office Box 579, Death Valley, California 92328, USA. Received August 22, 2005; accepted April 6, 2006 Published online November 30, 2006 1011 North American Journal of Fisheries Management 26:1011–1019, 2006 Ó Copyright by the American Fisheries Society 2006 DOI: 10.1577/M05-153.1 [Management Brief]