Pacific Southwest Research Station Graphic
Dusy Basin Baja trout Dusy Basin Mountain yellow-legged frog
Garter snake and frog Dusy Basin lake
graphic title - Sierra Nevada Aquatic Ecology Group


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Research Overview: The aquatic group focuses on the ecology and conservation of the native aquatic organisms in Sierra Nevada wilderness ecosystems (specific areas designated by the 1964 Wilderness Act) and understanding how various threats (e.g., cattle grazing, fish stocking) affect them. The high elevation lakes study was funded by the National Forest System and we surveyed over 2000 lakes to determine the effect of introduced trout on the native biota. This project has produced many peer-reviewed publications and it has also received media coverage in the New York Times, Seattle Times (see press coverage).


map of research areas - Knigs Canyon & John Muir WildernessHigh Mountain Lake Fish Stocking Studies
: 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).

Map of research areas Kings Canyon National Park & John Muir Wilderness, Sierra Nevada, California


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.


Mountain Yellow-legged Frog and Mountain Garter Snake Behavioral Ecology and Life History Studies: Kathleen Matthews and Karen Pope are conducting studies on the behavioral ecology and life history of R. muscosa in Kings Canyon National Park. A habitat and movement study using radio-transmitters found that R. muscosa use different aquatic habitats over the course of their activity period and that they readily moved between these habitats using both aquatic and overland pathways. The movements appear to be associated with seasonal migrations between breeding, foraging and over-wintering sites. Before this study, it was assumed that R. muscosa rarely occur more than a few hops from water, and that they overwinter in the deepest parts of lakes. Matthews and Pope found movements over 66 m across dry land, and also found that some frogs overwinter in nearshore ledges. A frog translocation study using radio-transmitters was also conducted in 1999, and the results are currently being analyzed.

In 1997, Pope and Matthews initiated a passive-integrated transponder (PIT) study and have tagged over 600 mountain yellow-legged frogs in Dusy Basin, Kings Canyon National Park. Every summer they conduct mark-recapture surveys on the population to gain information on growth rates, seasonal movement patterns, site fidelity, reproduction, population structure, and environmental effects on survival. They have found that the frogs move among the lakes and ponds in the basin and that adult frogs display site fidelity returning to the same water bodies from year-to-year. Summer and fall droughts seem to have an adverse effect on survival especially when trout occur in the larger, deep lakes and frogs are forced to breed in more shallow ponds that may dry up or become too shallow for winter survival. Because introduced trout currently occur in the main lake of the basin, this information will serve as a baseline to compare to the population structure, survival and behavioral ecology of the frogs if fish are removed from the basin.

Because little is known about the longevity or ages of R. muscosa or what factors affect their growth rates, the Aquatic Ecology Group is also initiating age and growth studies of mountain yellow-legged frogs over different elevations and latitudes throughout the Sierra using skeletochronology. They will conduct this initial aging study on mountain yellow-legged frogs and collect frog toes throughout the Sierra Nevada over a range of elevations from about 5,000 feet to 12,000 feet.

The dramatic amphibian declines reported worldwide also have important effects on their predators. In the Sierra Nevada, where amphibian declines are now well documented and some are closely tied to the introduction of non-native trout, the mountain garter snake, Thamnophis elegans elegans, preys predominately on amphibians, and recent evidence suggest they too are in decline. The introduction of nonnative trout has led not only to the decline of amphibians, but also to the decline of garter snakes. In the summer of 2001, Matthews and Pope will initiate demographic, feeding, and habitat studies of the high elevation garter snake to further understand its basic ecology and response to amphibian declines.

Livestock Grazing, Golden Trout, and Streams in the Golden Trout Wilderness, California: The Aquatic Ecology Group has also studied the impacts of livestock grazing on golden trout Oncorhynchus mykiss aguabonita and their habitat inside and outside of livestock exclosures in the Golden Trout Wilderness, California. Studies have been conducted on the movement ecology, habitat preferences, and population dynamics of golden trout by comparing recovering areas inside cattle exclosures to those areas outside cattle exclosures that are still grazed. The results of our studies have prompted more protective management of grazing riparian areas on the Kern Plateau. This study documented that California golden trout used and selected habitat features typically damaged by cattle grazing (undercut banks aquatic vegetation, and sedge) within pools and runs and avoided habitat features (bare and collapsed banks) typically caused by cattle grazing. Grazing management that seeks to protect habitat features preferred by California golden trout must employ strategies that protect undercut banks, sedge, and aquatic vegetation, and reduce bare and collapsed banks.

For further information about our research please visit our publications link - some available in pdf format.

forest service logoPacific South West Research Station
P.O. Box 245, Berkeley, CA 94701-0245
Telephone: (510) 559-6300
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