Collection of larval and early juvenile humpback chub, Gila cypha, from the Little Colorado River in Grand Canyon for use in translocation experiments

Authors: Rylan Morton-Starner, David L. Ward

Year: 2012 (xliv)

Abstract

Large numbers of juvenile humpback chub, Gila cypha, are needed for translocation experiments into tributaries of the Colorado River in Grand Canyon. These translocation efforts are limited by the number of fish large enough to be PIT tagged, <100 mm TL, that can be removed from the Little Colorado River without having potentially adverse impacts on the existing population. We evaluated the feasibility and techniques for capturing larval humpback chub from the Little Colorado River in spring 2012 for subsequent rearing in captivity and future translocation. Larval and early juvenile humpback chub were captured from mid to late May at 1.9 and 10.4 km upstream from the confluence. Larval humpback chub were easily distinguishable from suckers by this date and were concentrated in shallow areas of low flow under overhanging boulders or vegetation. Three hundred humpback chub were captured with a 2-mm mesh hand net, distributed approximately evenly into 4 plastic bags containing 1 L of river water each, pressurized with oxygen, hiked to the canyon rim, and transported by pickup to the Rocky Mountain Research Station in Flagstaff, AZ. Fish were held in a recirculating 500-L fiberglass raceway at 20°C and fed live brine shrimp and flake feed twice daily. Mortality during transport was low, 6 fish, but subsequent mortality over the next two months approached 30 percent. When fish reached 35 mm TL, they were moved into a 3,000-L tank and experienced little subsequent mortality. Capture and rearing of larval or very early juvenile humpback chub from the Little Colorado River for use in subsequent translocation experiments is feasible, but methods for rearing and feeding in captivity need to be refined, with a focus on maintaining fish in larger more natural settings to reduce fluctuations in water quality and stress related mortality.