Monitoring the status of the endangered Borax Lake chub, Gila boraxobius, in a geothermal lake in southeastern Oregon

Authors: Paul Scheerer, Steve Jacobs

Year: 2008 (xl)

Abstract

Borax Lake chub, Gila boraxobius, is a small minnow that is endemic to a natural 4.1 hectare geothermally-heated alkaline lake perched ten meters above the desert floor in Oregon’s Alvord basin. The Borax Lake chub was listed as endangered under the federal Endangered Species Act in 1982 due to threats of habitat alteration caused by geothermal energy development and alteration of the lake shore crust to provide irrigation to surrounding pasture lands. From 2005-2008, the Oregon Department of Fish and Wildlife developed survey protocols to monitor population abundance using mark-recapture protocols and snorkel index surveys. We found that snorkel surveys lacked sensitivity to detect all but major changes in population abundance. We found that we could obtain mark-recapture estimates of the Borax Lake chub with a relative precision of +14-20% while marking approximately eight percent of the population and handling approximately 20 percent of the population. With a precision of +14-20%, we have the ability to detect a 26-34% decline in abundance. We will compare these results to previous monitoring efforts that occurred in 1986-1997 when a significantly larger effort and proportion of the population was sampled. I will also discuss the substantial progress has been made in reducing threats to the habitat which have improved the conservation status of this species, the primary remaining threats, (increased recreation use, potential geothermal development, and nonnative species), and provide recommendations for future investigations and monitoring.