Does size matter in post-stocking survival of roundtail chub when released into a river with hungry predators?

Authors: Laura Tennant, David Ward

Year: 2016 (xlviii)

Abstract

Programs to recover rare or endangered fishes commonly rely on hatcheries for supplemental stocking of rare fish into areas with depleted populations. Roundtail chub Gila robusta is one such fish that has experienced severe declines in number and distribution in Arizona in recent years. Thousands of roundtail chub are reared annually at the AZGFD Bubbling Ponds Native Fish Conservation Facility and stocked into the Verde River and its tributaries as part of ongoing recovery efforts for this species. Hatchery-reared native fish typically suffer high mortality rates when stocked into natural environments with established populations of introduced fishes. Piscivorous fishes are able to select for size specific prey based on prey body depth and t he gape size of the predator. These relationships indicate that at the size at which roundtail chub are commonly stocked they are highly vulnerable to predation. We assessed survival of hatchery-reared roundtail chub with two electrofishing efforts, sixteen and eighty days post-stocking. Size differences of fish between initial and post-stocking efforts were apparent. We conclude that size of hatchery-reared fish may need to be considered prior to stocking and that a total length of at least 150 mm is needed to alleviate post-stocking predation pressure on roundtail chub in the upper Verde River.