USDA Forest Service

Pacific Southwest Research Station
Pacific Southwest
Research Station

800 Buchanan Street
Albany, CA 94710-0011
(510) 883-8830
United States Department of Agriculture Forest Service. USDA logo which links to the department's national site. Forest Service logo which links to the agency's national site.

Research Topics Ecosystem Processes

Sierra Nevada Ecosystems

Impacts of invasive species (non-native trout) on native biota of Wilderness lakes and future restoration strategies for balancing fish stocking and native species.

The Research

Since 1995, the US Forest Service Pacific Southwest Research Station Aquatic Ecology Group has been involved in studying the effects of the widespread introduction of non-native trout on the native high elevation lake fauna in the Sierra Nevada. Kathleen Matthews and Roland Knapp (UCSB, Sierra Nevada Aquatic Research Laboratory) conducted the High Mountain Lake Project where the impacts of fish stocking were assessed by surveying over 2000 lakes in the John Muir Wilderness (where fish stocking continues) and the adjacent Kings Canyon National Park (where fish stocking was terminated).

The results of the studies indicated a strong negative effect of introduced trout on the distribution and abundance of the mountain yellow-legged frog, Rana muscosa, and the Pacific treefrog, Hyla regilla, and these results are published in Conservation Biology, and International Journal of Wilderness, and Copeia. The research also found a deleterious effect of non-native trout on macroinvertebrates, zooplankton, and the mountain garter snake Thamnophis elegans elegans, a native predator that is apparently dependent upon amphibians. The researchers observed a strong association between amphibian presence and garter snake presence and the probability of finding snakes in lakes with amphibians was 30 times greater than in lakes without amphibians. Moreover, lakes with snakes had higher numbers of amphibians than did lakes without snakes. The introduction of trout into an ecosystem can have serious effects, not just on their prey, but also on other predators in the ecosystem.

More recent analyses of the lake survey data looked at the resistance and resilience (the degree to and the rate at which a system returns to its previous configuration once the perturbation is removed) of the alpine communities once fish were removed and the results are reported in Ecological Monographs. Faunal assemblages in the study lakes had low resistance to fish introductions, but in general showed high resilience once fish were removed. The results of the high mountain lake study are instrumental for conservation of native species in the Sierra Nevada.

Last Modified: Aug 29, 2016 10:56:05 AM