"Our knowledge of Lake Tahoe's nearshore fishery is very limited. There have only been a few sporadic assessments and documentaries of the nearshore fishery in the past 60 years, and no studies were conducted in the last 20 years after the establishment of invasive, warmwater fishes," Ka Lai Ngai, a researcher in the University's Department of Natural Resources and Environment said.
This knowledge gap stimulated the process of conducting a contemporary assessment and developing ecologically relevant metrics to assess the nearshore fishery. Chandra proposes one of those metrics be ultraviolet radiation exposure, and a new TRPA threshold be developed for it, the Ultraviolet Attainment Threshold. The UVAT is a target value for water clarity based on surface UV exposure during peak spawning season, and experimentally derived UV exposure levels lethal to larval warmwater fish.
"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.
Tahoe watchers are accustomed to hearing about clarity of the water, and it's decline, and UV radiation penetration is affected by clarity. In Lake Tahoe the average annual Secchi transparency dropped from 102 feet in 1968 to 69 feet by 1998. The summer 2010 Secchi reading was 68 feet. During this same time a number of nonnative warmwater fish species became established in portions of the lake suggesting that decrease in water transparency may create a refuge for nonnative species that are less sensitive to the optical properties of water such as ultraviolet radiation.
To get a more objective, quantifiable measure, and ra
|Contact: Mike Wolterbeek|
University of Nevada, Reno