Laughlin Lagoon Avian Predation Monitoring

Authors: Layne Huber

Year: 2018

Abstract

Reclamation and other stakeholders perform a variety of conservation related activities in the region. The conservation of Bonytail Chub, Gila elegans, and other native fish species is currently managed under the Multi-Species Conservation Program (MSCP) Fisheries Program. There are three components to the Fisheries Program; continued monitoring of existing Bonytail populations, population augmentation through repatriation, and hatchery research and efficiency. Existing population monitoring indicates that fish are not self-replacing in the wild (Minckley et al. 2003). This lack of success on the part of native fish has largely been attributed to predation of larvae and juveniles by non-native fish (Minckley 1983, Minckley 1991). The augmentation effort has attempted to circumvent this predation risk by releasing hatchery stock at the sub-adult stage (>300mm) which should be large enough to avoid predation by non-native fish (Mueller 1995). However, MSCP staff are now concerned with avian predation of repatriated sub-adult fish. The Lower Colorado River is used by several resident and migratory piscivorous (fish-eating) bird species including cormorants, Phalacrocorax spp., Great Blue Herons, Ardea herodias, and Osprey, Pandion haliaetus. Other species of interest include American White Pelican, Pelecanus erythrorhynchos, Great Egrets, Ardea alba, Common Mergansers, Mergus merganser, and grebes, Aechmophorus spp. Currently, the effects of avian predation are unknown. However, if the threat level could be determined, MSCP could attempt to mitigate for it by altering release strategies or altering stocking numbers. This report details on-the-ground and remotely sensed avian predation monitoring conducted in 2015, 2016, and 2017 as part of the MSCP at Laughlin Lagoon, NV. The goals of this study are to 1) determine the minimum number of fish from each Bonytail Chub stocking effort that are eaten by birds, and 2) determine the relative abundance of piscivorous bird species at the Laughlin Lagoon release site.