New research by Associate Professor of biology Jennifer Dever and graduate student Ryan
Peekew on yellow-legged frogs raises concerns about California waterways.
The dramatic population decline of the foothill
yellow-legged frog in a number of California rivers is a canary in a coal mine,
pointing to poor waterway management and potentially widespread ecological
breakdown, according to the latest findings by two University of San Francisco researchers.
by USF Associate Professor of biology Jennifer Dever and graduate student Ryan
Peek found that the population of the yellow-legged frogs (native to California
and Oregon) – whose life revolves around and depends on running rivers and
streams – has dropped by 50 percent from historic levels.
In a first-of-its-kind analysis, Dever and Peek used DNA
samples to show that yellow-legged frogs (A Species of Special Concern as
designated by the California Department of Fish and Game, indicating that they
could be listed as “threatened” or “endangered” if the population decline
continues) living along the American and Feather rivers are less genetically
diverse than they were in the past, potentially handicapping their ability to
adapt to environmental changes.
“Our data from unregulated (free flowing) rivers and
regulated (dammed or levied) rivers indicate that dams are causing a decrease
in the foothill yellow-legged frogs’ genetic diversity,” Dever said.
In turn, decreased genetic diversity has likely contributed
to the frog’s population plummet.
“People need to realize that these frogs are indicators of
the overall health of the ecosystem,” Dever said.
Such degradation may have ramifications beyond amphibians,
including impacting species that depend on the benefits that ecosystems provide
such as clean water, food, purification of human and industrial wastes, and
habitat for plant and animal life, Peek said.
While the likelihood of Californians choosing to demolish a
substantial number of the 800 dams in Northern California to allow rivers and
streams to revert to their natural water flow patterns is improbable, there are
effective strategies that could be used to better manage the dams and levies
affecting the frogs.
“Generating renewable energy is a great goal but there are
ways that dams can be operated that lessen the impact of altered water flows on
native wildlife and research has shown that flows that mimic the natural flow,
with peak flows in the late winter/early spring that taper down throughout the
summer, are much better for frog breeding and survival than having flows that
peak at unnatural times,” Dever said.
With additional research on the horizon, Dever and
Peek plan to publish their latest findings, which follow Dever’s earlier
research, this fall. Recommendations on how to better manage the
relevant rivers are likely to follow.