Native fish populations at Lake Tahoe have seen a sharp decline in the past 60 years, according to the latest lakewide study from researchers at the University of Nevada, Reno.
During a yearlong study, Sudeep Chandra, an assistant professor in the university's Department of Natural Resources and Environment, and a research team found 58 percent of the 26 historically sampled locations around the lake showed a decline of species or no native species at all.
"The numbers are alarming, and likely caused by multiple stressors in the near shore zone," Chandra said in a statement. "The good news is that the composition is there. The bad news is the decline in number, the decline in native species and the proliferation of nonnative fish species."
For the study, the team focused on the nonnative warm water fish species bluegill and largemouth bass. Both species were illegally introduced into the lake and are now common in the Tahoe Keys.
Since the introductions, native Lahontan redside shiner and speckled dace populations declined or were virtually eliminated from the Keys.
Several species of nonnative cold water sport fish, such as Mackinaw, rainbow, brown and brook trout, have also been introduced to Lake Tahoe to provide recreational sport fishing. Mackinaw trout, brought here from Michigan in 1894, contributed to the extinction of Tahoe's native Lahontan cutthroat trout in 1939, Chandra said.
The lake's clarity may have contributed to the spread of the invasive fish.
Clarity dropped from 102 feet in 1968 to 69 feet by 1998. The summer measurement for 2010 was 68 feet.
The decrease in transparency may create a refuge for nonnative species that are less sensitive to the optical properties of water such as ultraviolet radiation, Chandra said.
"We've found that decreased ultraviolet radiation is one of the major factors in the changes that make it easier for invasive species to proliferate, including fish, plants and mollusks," Chandra said.
Eleven of 28 near shore sites were identified as having a high potential for improvement in the amount of ultraviolet light during the study.
Chandra and his team have suggested the Tahoe Regional Planning Agency and other land use agencies concentrate on efforts to protect the lake's near shore area.
The researchers propose the TRPA develop a metric to measure ultraviolet radiation exposure in the near shore as one of its environmental goals, known as thresholds.
The study also recommends establishing a management plan to protect near shore habitats critical to native fish.