Large-Scale Monitoring of Humpback Chub in the Grand Canyon: Determining Key Vital Rates and Informing Broader Conservation Insights

Authors: Benjamin Miller, Lindsay Hansen, Maria Dzul

Year: 2024

Abstract

Native fishes in the Colorado River Basin are highly imperiled, including Humpback Chub (Gila cypha), which persists in its largest population within the Grand Canyon, despite substantial ecosystem alterations. To evaluate this keystone population, the U.S. Geological Survey (USGS) Grand Canyon Monitoring and Research Center initiated the Juvenile Chub Monitoring (JCM) study, which has assessed vital rates for over a decade (2012-present) in the Colorado River in the Grand Canyon. The JCM conducts multiple intensive surveys (n = 3 or 4) annually, sampling ~ 22 river kilometers (rkm) at up to two discrete reaches (in eastern and western Grand Canyon) using remote passive integrated transponder (PIT) tag antennas, alongside three passes of electrofishing and six passes of hoop netting. Specifically, these monitoring trips currently collect ~ 2,100 hoop nets, conduct 900 electrofishing passes, and deploy 288 antenna-days per year, demonstrating the large effort involved in data collection. We describe spatial and temporal patterns in vital rates such as abundance, survival, and growth of Humpback Chub in eastern and western Grand Canyon over the last decade and find differences in growth and survival in the two sampling reaches. Additionally, the breadth of data collected also allows for exploration of supplementary questions that could benefit native fish conservation. We explore several such avenues of further investigation, including sampling efficiency (i.e., the ‘depletion effect’), potential differences in survival rates between capture gear types, and demographic information of other native and non-native species of concern. Given adequate resources, initiating similar large-scale projects elsewhere in the Colorado River Basin could generate useful data to enhance conservation strategies for other imperiled native fish populations, potentially providing insights that smaller-scale studies may overlook.