Research Topics Ecosystem Processes
About this Research:
Sierra Nevada Ecosystems
Aseasonal pulsed flow effects on the foothill yellow-legged
frog (Rana boylii): Integration of empirical, experimental and hydrodynamic
Research Project Summary
study is a collaborative effort between the USDA Forest Service,
Pacific Southwest Research Station, Sierra Nevada Research Center,
the University of California, Davis, and an independent scientist.
The primary goal of the study is to better understand the effects
of pulsed flow releases resulting from hydroelectric power generation
on the foothill yellow-legged frog (Rana boylii).
The foothill yellow-legged frog is one of a few California amphibians
whose complete life cycle is associated with stream environments.
The life stages of the foothill yellow-legged frog occur along a
mobility continuum from immobile (eggs) to highly mobile (adults)
such that adaptations which improve survival rate vary in relation
to ontogeny. To avoid disturbance, the timing of this complex life
history and set of habitat preferences is synchronized with the
seasonality of runoff during the predictable cycle of wet winters
and dry summers occurring across the range of the foothill yellow-legged
frog. Over the last half century, the foothill yellow-legged frog
has declined dramatically, especially in southern California and
the southern Sierra Nevada mountains. Dams and reservoirs have been
cited as likely factors in this decline because they drastically
alter the disturbance regime and sediment budget of rivers in which
native species have evolved, resulting in permanent alteration to
instream habitats. The ensuing impact on foothill yellow-legged
frog survival has been a focus of study over the last decade, but
many knowledge gaps remain. Of primary concern to us in this proposal
are the short-term direct and indirect effects of extreme aseasonal
fluctuation in water discharge during the foothill yellow-legged
frog's larval rearing season.
to its declining status, foothill yellow-legged frogs have increasingly
become a focal species in water management planning, especially
in FERC re-licensing programs for hydroelectric dams. However, due
to the dispersed nature and different agency involvement in the
licensing efforts, a comprehensive assessment of pulsed flow effects
on foothill yellow-legged frogs has yet to be conducted. With such
an assessment, our understanding of the influence of pulsed flows
relative to foothill yellow-legged frogs survival will be improved
and obvious knowledge gaps could be identified. Once these gaps
are clearly identified, it will be possible to develop hydrodynamic
modeling tools to determine how changes in habitat availability
and habitat heterogeneity resulting from differing flow regimes
affect the reproductive success and survival of foothill yellow-legged
frogs. Finally, to link this habitat-based modeling approach to
actual rates of survival and reproductive success, controlled experiments
on foothill yellow-legged frog physical tolerances are needed. In
particular, data are lacking on the tolerances and responses of
the larval life stage of the foothill yellow-legged frog to pulsed
To better understand the effects of pulsed flows on foothill yellow-legged
frogs, we are addressing the following objectives in a two phased
Document relationships between characteristics of pulsed flows (e.g.
timing, ramping rates, ratio to base flow) and survival, reproductive
success, and habitat suitability for all life stages of the foothill
yellow-legged frog through a review and analysis of existing data
Identify specific knowledge gaps regarding aspects of fluctuating
or pulsed flows (e.g. timing, duration, ramping rates, volume) and
their impacts on foothill yellow-legged frog survival rates, reproductive
success, and habitat suitability.
Address specific knowledge gaps identified in Phase I with a series
of laboratory and field experiments designed to quantify larval
swimming abilities and behavioral responses to changes in shear
stress created by manipulations of depth, velocity, and substrate.
Develop a model-based methodology to evaluate changes in habitat-scale
hydrodynamics from a series of low and high pulse flow scenarios
and subsequent changes in habitat availability and heterogeneity.
Use results from lab and field manipulations to assess how modeled
changes in habitat availability and heterogeneity may influence
foothill yellow-legged frog survival and reproductive success. By
integrating these two components we will be able to translate model
predictions regarding habitat parameters into actual effects on
various life stages of the foothill yellow-legged frog.
Methods and Design
We are conducting a two-phased project conducted over two years
to address the above described research and water management needs.
Phase I involves a review of published and unpublished literature,
collation and analysis of data from recent studies, and identification
of knowledge gaps. Phase II then directly applies the information
gathered in Phase I to refine the focus of experiments regarding
relative vulnerabilities of various life stages and to develop hydrodynamic
models of foothill yellow-legged frog habitat. In Phase I, data
are being analyzed with respect to quality and in terms of direct
and indirect effects on foothill yellow-legged frogs. Variables
representing foothill yellow-legged frog status, life stage, abundance,
reproductive success and habitat components (depth, velocity, substrate)
are being summarized and analyzed relative to pulsed flow events
and characteristics (timing, duration, ramping rates, flow magnitude
II consists of complementary experimental and hydrologic modeling
components. The experimental component of Phase II includes both
field transplant and laboratory flume experiments. In field experiments,
foothill yellow-legged frog larvae are moved from shallow margins
into deeper, higher velocity areas and their response observed.
Laboratory flume experiments provide opportunities to vary water
velocities and availability of cover and record the response of
different aged larvae. Phase II modeling is being done using River
2D, a two-dimensional depth averaged finite element model, that
is used by California Fish and Game and others in fish habitat evaluation
studies. The output from the modeling scenarios are being analyzed
in a variety of ways to determine how velocities (magnitude and
direction), depths and habitat types change as flow fluctuates.
Changes in velocity magnitude and direction at each modeled discharge
will provide information on whether mobility thresholds of vulnerable
life stages are exceeded. Changes in habitat availability and heterogeneity
will provide information on base flow discharges that provide the
highest proportion of suitable habitat for all life stages.
Application of Research Results
The integrated results of this work should provide a better understanding
of the current impacts of pulsed flows on foothill yellow-legged
frogs along with a model-based methodology that could be used to
mitigate impacts on various aquatic species in future pulsed flow
Study sites for field experiments and hydrodynamic modeling have
not yet been selected,but will be in low-mid elevation streams on
the west slope of the Sierra Nevada, with a known R foothill yellow-legged
frog populations, and downstream of a hydroelectric facility. Laboratory
experiments will be conducted in an artificial stream/laboratory
flume at the USFS PSW Redwood Sciences Laboratory in Arcata, California.
1.)Lind, A. 2) Yarnell, S. 2) Mount, J. 3) Kupferberg, S.
1)USDA Forest Service
Pacific Southwest Research Station
Sierra Nevada Research Center
2) University of Calfiornia, Davis
3) Questa Engineering
The study was funded by the Public Interest Energy Research Program
of the California Energy Commission and the Division of Water Rights
of the State Water Resources Control Board via the Pulsed Flow Program,
Center for Aquatic Biology and Aquaculture, University of California,
Publications and Products
* Previous research related to this project includes Lind et al. 1996.
Pulsed Flow Effects on the Foothill Yellow-Legged Frog (Rana boylii): Ingetration of Emplirical, Experimental and Hydrodynamic Modeling Approaches. Pier Final Project Report