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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).
 High
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.
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Pacific
South West Research Station 