Miami researchers identify significant decline in Lake Tahoe minnow population

Native minnow populations in Lake Tahoe have dropped significantly over the last 20 years, most likely due in part to the lake’s long-term loss of clarity and increased competition from non-native fish, according to research by a team of scientists at Miami University, the University of Nevada, Reno, and University of California at Davis, Tahoe Environmental Research Center.

Fish densities, mostly native minnows, surveyed in shallow depths near the lake’s shore, declined 58 percent between 1988 and 2009, researchers found. The population of one minnow type, redside shiners, dropped between 24 percent and 100 percent in 42 percent of surveyed locations from 1988 to 2009.

The scientists found a strong link between water clarity through ultraviolet (UV) light penetration and biodiversity in Lake Tahoe, suggesting that water transparency to ultraviolet radiation may be an additional factor that regulates the current and future distribution of non-native fishes.

A goal of the Miami researchers is to develop a water clarity threshold, based on measured UV tolerance levels of non-native versus native fish, which could be used by lake managers as a target water clarity measure to prevent the further spread of non-native fish and to limit their negative impact in the lake.

Main Miami researchers on the project included Craig Williamson, Ohio Eminent Scholar in Ecosystem Ecology, Jim Oris, professor of zoology and associate dean for research and scholarship, Andrew Tucker, zoology doctoral student, and Amanda Gevertz, former zoology master’s student. Williamson and Oris, both long-term researchers of Lake Tahoe, were co-principal investigators of the study funded by the U.S.D.A. Forest Service grant, "NICHES: Nearshore Indicators for Clarity, Habitat and Ecological Sustainability.”

A study recently published in the journal Ecology by Tucker, Williamson, Oris, Kevin Rose, zoology doctoral student, and others, demonstrated that maintaining high ultraviolet transparency in Lake Tahoe may be the key to reducing invasion of warm-water fish, such as bluegill, that threaten the native fish species in the lake.

Other Miami researchers in Oris and Williamson’s labs include Sandra Connelly (Ph.D. 2009), and Kevin Rose (Ph.D. May 2011), who played significant roles in the initial portion of the project, Annie Bowling (M.S. 2010), Molly Mehling and Jeremy Mack, current doctoral students, postdoctoral fellow Carrie Kissman, Ian Lizzadro-McPherson, current masters student, and Erin Overholt (Miami M.S. 2001), lab manager. Undergraduates include junior Graham Hughes and Michael Cohen, who graduated in May 2010.

Among other studies, Oris has been studying the impacts of UV and motorized watercraft in Tahoe since 1998, and led a three-year analysis of environmental quality in lakes of the Tahoe region beginning in 2000. Williamson has been monitoring UV transparency in Lake Tahoe in since 2006.