Common carp ages, back calculations and growth rates at a large backwater above Lees Ferry in Glen Canyon, Colorado River

Authors: Pilar Wolters

Year: 2013 (xlv)

Abstract

Before Glen Canyon Dam closed in 1966, common carp (Cyprinus carpio) was one of the most abundant fish species in the Lees Ferry stretch of the Colorado River. After closure of the Dam, the hypolimnetic release of water drastically altered the water temperature at Lees Ferry, favoring an introduced blue-ribbon rainbow trout fishery. In July water temperatures range from 9.5- 10.5„aC, which is not conducive to native fish or carp. Carp generally begin to spawn at temperatures of 17- 27„aC. Within the Lees Ferry stretch these temperatures are only found within sloughs or backwater areas. At river kilometer 5.6 to 5.9 (-12 mi up from Lees Ferry) there is a relatively large backwater slough that maintains water temperatures of 13- 17„aC and 12.5- 15.5„aC at 20cm and 100cm below the surface respectively. Carp are the dominant fish species within the slough, comprising 80-90% of the fish. In 2010 the population of carp in the slough was estimated to be 479 (95% CI 329-785). We believe carp are utilizing the slough for reproduction as 56% of the carp sampled in 2013 were reproductively active. In 2013 dorsal spines were collected for determining age and growth. Back calculated growth rates for carp in the slough were compared to growth rates from carp collected in the mainstem Colorado. This slough is also believed to serve as a refugium for native flannelmouth suckers (Catostomus latipinnis) until they spawn in the nearby Paria River. Flannelmouth suckers migrate up to the slough from as far downstream as 233 km (145 mi). Carp may be preventing or hindering flannelmouth growth, survival, and reproduction in this rare and important warmwater habitat in the Colorado River.