Colorado pikeminnow habitat availability, use, and selection in the San Juan River, New Mexico and Utah.

Authors: Ernesto A. Hoz, Paul Holden

Year: 2009 (xli)

Abstract

Native to the Colorado River basin, Colorado pikeminnow (Ptychocheilus lucius) is an endangered fish that occurs in the San Juan River, New Mexico and Utah. As with many other native fish in the American southwest, the distribution and abundance of this large piscivorous cyprinid has declined as a result of anthropogenic changes to its physical and biological environment. As part of recovery efforts in the San Juan River, over 2 million age-0 and age-1 Colorado pikeminnow were stocked from 2002 to 2008. However, these age-0 and age-1 fish are no longer found during fish-monitoring surveys after about four and two overwintering periods, respectively. The factor(s) precluding recruitment of these fish into the adult population are unknown. In this study we assess habitat availability and use by young Colorado pikeminnow and other native and non-native species and determine whether or not there is evidence of selection for particular habitat types. From 2007 to 2009 we conducted biannual fish and habitat surveys along three 1-mile reaches along the San Juan River. Results suggest that young Colorado pikeminnow select for specific habitat types; fish with total length (TL) less than 100 mm appear to select for low-water velocity habitats with fine substrates including embayment, pool, and backwaters. Colorado pikeminnow in this size class appear to select against riffles, cobble shoals, and slackwaters. Consistent with previous research documenting shifts in diet composition by young Colorado pikeminnow, we find that Colorado pikeminnow with TL over 100 mm appear to select for cobble shoal habitat that is characterized by relatively higher water velocities and large substrate. Pikeminnow in this larger size class also appear to select against run habitat. Our assessment of habitat availability indicate that while young Colorado pikeminnow use habitats that are prevalent along the reaches sampled (e.g., run habitat), habitat types that appear to be selected for by young Colorado pikeminnow are rare. While it would be necessary to sample more reaches over the course of more years to verify findings of habitat selection, this study provides more insight into specific low-velocity habitat types that are important for Colorado pikeminnow. Information about habitat use, selection, and availability could be used to strategically prioritize areas for improvement of habitat quality.