Population estimates for Humpback Chub, Gila cypha, and Roundtail Chub, Gila robusta, in Westwater Canyon, Colorado River, Utah, 2016-2017

Authors: Brian Hines

Year: 2019

Abstract

Westwater Canyon on the Colorado River contains one of the five remaining populations of the endangered Humpback Chub, Gila cypha, in the Upper Colorado River Basin. Westwater Canyon also contains a large population of Roundtail Chub, Gila robusta, which are listed as a species of concern throughout their range. Recovery goals identified by the Upper Colorado Recovery and Implementation Program require maintaining several populations of Humpback Chub within the Upper Colorado River Basin. Monitoring efforts are essential to evaluate the population of Humpback Chub in Westwater Canyon and meet the recovery goals. Trammel nets, electrofishing gear, and submersible antennas were used to sample humpback and Roundtail Chubs in Westwater Canyon in 2016 and 2017. Important metrics including catch rates, size structure, and population size were calculated for Humpback and Roundtail Chub. Catch rates of Humpback Chub in 2016 and 2017 were 0.3 and 0.5 fish/hr, respectively. Catch rates of Roundtail Chub in 2016 and 2017 were 1.37 and 0.98 fish/hr, respectively. The population size of Humpback Chub in 2016 and 2017 were estimated at 2,002 (95% CI 1118-2886, SE=430, CV=0.23) and 3,656 (95% CI 1,177-6,133, SE=1,097, CV=0.30), respectively. The population size of Roundtail Chub in 2016 and 2017 were estimated at 7,916 (95% CI 6,320-9,512, SE=811, CV=0.10) and 11,300 (95% CI 8,055-14,545, SE=1,645, CV=0.15), respectively. In this presentation, I will describe recent monitoring activities of Humpback and Roundtail Chub in the context of historical data for the Westwater population.