Assessing habitat availability and use by endangered Colorado pikeminnow, Ptychocheilus lucius, and other native and non-native fish in the San Juan River, New Mexico-Utah

Authors: Ernesto A. Hoz, Paul Holden

Year: 2008 (xl)

Abstract

We investigated habitat availability and use by native and non-native fishes in two reaches along the San Juan River, New Mexico and Utah. Preliminary results of this on-going study are presented. Chi-squared selection ratios based on habitat availability and use data collected in summer of 2007 indicated that age-1 Colorado pikeminnow, (,i>Ptychocheilus lucius), selected two habitat types, eddy and cobble shoal. In contrast, Chi-squared analyses suggested that the entire fish community, both natives and non-natives, selected against cobble shoal. Speckled dace, (,i>Rhinichthys osculus), was the only species that also appeared to select eddy habitat. Our findings highlight the importance of cobble shoals for age-1 Colorado pikeminnow and that relatively few other fish species prefer this habitat type. Further, observed patterns of selection and selection against particular habitat types by native and non-native fishes provided evidence of the high overlap in habitat use. Both native and non-native fishes appeared to select isolated pool and pool habitat, while selecting against cobble shoal, run, and riffle habitats. Our results support findings from previous studies that have documented overlaps in resources used by native and non-native fishes in the San Juan River. Observed patterns of habitat selection and overlap highlight the potential for negative interspecific interactions (e.g., competition) between native and non-native fishes. While previous research has identified low water velocity habitat as important for small Colorado pikeminnow, this study allows the identification of specific habitat types with some current, such as cobble shoals and eddies, that are important for age-1 Colorado pikeminnow. Ongoing efforts aim towards the assessment of differences in habitat use by age-0 and age-1 pikeminnow, and differences in habitat use during different times of the year (i.e., spring, summer). As others have suggested, understanding which habitats are needed by each life stage in this highly modified system has important implications for the management and conservation of Colorado pikeminnow.