Jonathan Stead
Graduate Group in Ecology, Univ. of California, Davis
Davis, California
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ABSTRACT
STEAD, JONATHAN, HARTWELL WELSH, and KAREN POPE
Graduate Group in Ecology, UC Davis, Davis, CA,
US Forest Service, Pacific Southwest Research Station, Redwood Sciences Laboratory, Arcata, CA.,steadje@yahoo.com
Critically Low Numbers of Cascades Frog in the Lassen Region
We conducted a cooperative inter-agency investigation into the status of native amphibians and nonnative fishes in lentic habitats at Lassen Volcanic National Park. Census surveys at Lassen Volcanic National Park were conducted during summer 2004, and results of surveys that we conducted in the Thousand Lakes and Caribou Wilderness areas during summer 2002 are also presented here. Visual encounter surveys were conducted to identify presence, species, life stage and relative abundance of amphibians, and timed gill net sets or visual surveys were used to identify fish presence, species, and relative abundance. Habitat data were also collected. We use generalized additive models to examine site attributes associated with amphibian occurrences, including the presence or absence of fish. Herpetofauna detected include the Pacific treefrog (Hyla regilla), western toad (Bufo boreas), long-toed salamander (Ambystoma macrodactylum), Cascades frog (Rana cascadae), rough-skinned newt (Taricha granulosa), western terrestrial garter snake (Thamnophis elegans), and the common garter snake (T. sirtalis). Fish species detected include three species of trout (Family: Salmonidae), five minnow species (Family: Cyprinidae), and the Tahoe sucker (Catostomus tahoensis). Our models suggest that populations of long-toed salamanders and Pacific treefrogs are less likely to be found in water bodies supporting fish. The Cascades frog was only detected at three sites, and could not be analyzed statistically. We believe that the Cascades frog is in immediate risk of extirpation from the Lassen region. Although fish clearly adversely affect palatable amphibian species, a number of considerations lead us to believe that fish are not the main driver behind the observed regional decline of Cascades frog. Factors outside the scope of this investigation may play an important role in declines observed in the Lassen region.
1 comment:
Very interesting talk. Thanks for studying the decline of these frogs. There does not seem to be a lack of them in fish filled tributaries of the Humptulips River in Western WA.
They lay their eggs in masses of downed tree branches in sluggish creeks. After last winter there is a lot of debris in the creek and lots of Cascade frogs. (Fish too!)
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