Shifting the Bonytail management mindset toward innovation in the upper Colorado River basin

Authors: Koreen Zelasko, Zane Olsen, Jared Smith, Brian Scheer, Ricardo Romero

Year: 2024

Abstract

Bonytail, Gila elegans, is endemic to the Colorado River Basin and listed as endangered under the Endangered Species Act. In the upper Colorado River basin (upper basin), Bonytail have been consistently reared and stocked since 1996 with little success; they are rarely encountered by any method more than a year after stocking. The Upper Colorado River Endangered Fish Recovery Program (Program) is changing the way it approaches Bonytail managementnot just tweaking existing actions, but deliberately shifting to ensure that every action taken for Bonytail aims to increase survival and expand the vision of what is possible in the upper basin’s hatchery system. The Program’s propagation workgroup embraced the shift by acknowledging that some recommendations in the species’ stocking plan had not yet been addressed, soliciting from hatchery staff the novel ideas they have been harboring, and requesting input and expertise from the lower Colorado River basin (lower basin). Ouray National Fish Hatchery (ONFH)-Randlett flow trained half of approximately 5,000 Bonytail stocked in spring 2024 and achieved statistically-significant higher velocities in treatment tanks using existing hatchery infrastructure. ONFH-Randlett and Wahweap State Fish Hatchery adjusted their established calendars and repeatedly stocked locations across seasons to better meet flow and temperature recommendations and understand those effects. Finally, adult Bonytail have been stocked into managed floodplain wetlands in hopes of increasing survival after release into mainstem rivers several months later. Over-summer survival of stocked fish within the wetlands is presumed low, with a maximum recapture rate of 13% during wetland draining. However, the presence of young-of-year Bonytail during wetland draining (often just a few but a high of 617 in 2023) confirmed the species’ capacity for wild reproduction in those habitats. Most rearing and stocking actions undertaken in the upper basin will be evaluated through future encounter rates from physical sampling and antennas. Other ideas proposed by hatchery managers and lower basin experts still in progress or under consideration by the Program include: provision of cover in hatchery tanks and ponds to reduce Bonytail stress, stocking of more but smaller Bonytail to emulate a possibly important life history strategy, stocking by boat to access more advantageous habitat, converting ONFH-Randlett’s water supply to a natural flow-through system from Green River surface water, and resumption of stocking voluntarily-spawned juvenile Bonytail into Lake Powell or elsewhere in the upper basin. Bringing Bonytail back from the brink of extinction will take more than typical propagation measures. The Program implemented some relatively easy ideas, and more innovation is still to come.