Status, Distribution, and Conservation of Native Freshwater Fishes of Western North America

Abstract

ABSTRACT Population abundance estimates conducted from 1998 to 2000 were completed for adult (>200 mm) humpback chub <em>Gila cypha</em> and roundtail chub <em>G. robusta</em> in Westwater Canyon on the Colorado River, Utah. Sampling was conducted annually using a three-pass mark–recapture approach. The primary method of capture was trammel netting with supplemental electrofishing on one pass per year. Separate abundance estimates were generated for each year of the study using the null estimator (M<sub>o</sub>) within Program CAPTURE. Results showed a decline in the adult humpback chub population between 1998 and 1999 and no change in abundance between 1999 and 2000. The adult roundtail chub population abundance in Westwater Canyon during this time period was relatively stable. Catch per unit effort (CPUE) data from this study and historic interagency standardized monitoring indicated a continued declining trend in mean CPUE for humpback chub that was significant. Mean CPUE for roundtail chub also showed a continued declining trend, but it was not statistically significant. The results of this study provide information to assess the current status of these two species and a point of reference for future population estimates of chub in the upper Colorado River basin.