Sigh, you can tell this article has me tearing my
too grey hair out. I've been posting about Pacific
tree/chorus frogs not breeding in fish filled lakes
for a couple years now.....
OKAY, this time I'll post the article ;-)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

BERKELEY
Cal biologist solves mystery of disappearing Sierra frogs

David Perlman, Chronicle Science Writer Thursday, May 13, 2004

The mystery of the disappearing frogs is an old one in the High Sierra, and now
a UC Berkeley biologist argues he has cracked the case and found a solution to
the critters' impending demise.
Stocking high-elevation lakes in the Sierra Nevada with hatchery-raised fish
began as far back as the 1880s, when miners hauled fingerling trout to the
lakes in milk cans on mule-back. By the 1950s, the introductions became
large-scale, using planes flying over the lakes to release fish by the hundreds
of thousands.
But since then, a species of amphibian, the mountain yellow-legged frog, has
declined almost to extinction in most of those lakes, according to Vance T.
Vredenburg, a UC Berkeley biologist who has hiked through the early June snows
of the High Sierra for the past eight years to learn what's killing them.
The frogs were once so abundant on the shores of the Sierra lakes that a
Berkeley wildlife survey team reported in 1915 that the surveyors couldn't help
stepping on hundreds of them.
A new study by Vredenburg offers the best evidence yet that rainbow trout are
primarily responsible for the frog's disappearance from hundreds of high
mountain lakes from Susanville in the north, to the Lake Tahoe region, and well
to the south of Kings Canyon National Park.
In eight years of carefully controlled experiments, Vredenburg used a cluster
of lakes as his laboratory in the Sixty Lakes Basin of Kings Canyon National
Park east of Fresno. The lakes lie in chains at elevation between 10, 000 and
11,500 feet.
From early June, after much of the snow melted and made access possible, until
October when the snows returned, he and his undergraduate assistants camped at
the lakes, making careful counts of trout and frog populations, and watching
how their numbers changed.
Vredenburg says that when he used gill nets to remove all the trout from any
lake where the frogs had almost disappeared, the few remaining amphibians
underwent a three-year population explosion.
In lakes that were never stocked, Vredenburg reports, the large populations of
frogs remained, but when he and his team moved a few trout into small
fenced-off areas where the frogs had laid their gelatinous egg masses, the
predatory fish swiftly consumed every one of the newly hatched tadpoles.
The results are published this week in the online edition of the Proceedings of
the National Academy of Sciences.
Experts have theorized about other causes: pesticides and herbicides drifting
into the mountains from Central Valley farmlands are a known cause of declining
frog populations. Global climate change that may be raising the temperature of
the icy mountain lakes could be another cause.
And a fungus called chytrid that attacks the mouth parts of tadpoles and kills
adult frogs has recently been detected in several species of Sierra amphibians,
including yellow-legged frogs. Vredenburg's newest research project is to track
the fungal disease and learn what role it may now be playing in their decline.
"There are at least 10,000 lakes in the High Sierra," Vredenburg said. "Ninety
percent to 95 percent of them hold introduced species of trout but no more
frogs at all. And there may be 200 lakes that have plenty of frogs, but few or
no fish.
"So the answer is pretty straightforward, and it doesn't get much simpler: with
no trout you get an immediate and dramatic response -- the threatened frogs
return, and some of the High Sierra's natural biodiversity returns, too."
According to David Graber, science adviser to the Sequoia and Kings Canyon
National Parks, Vredenburg's study is of major importance. He says park
officials have begun a 10-year experiment to see whether removing fish from 11
high-elevation lakes will restore the frog populations there. Six lakes are
expected to be free of trout this summer, he said.
But politics always intervenes in environmental questions. Brett Matzke, the
western Sierra manager of the statewide angler's organization, CalTrout, agrees
that "it appears necessary to remove trout from at least a few lakes in order
to create habitat for viable (frog) populations."
As a result, he said, it would be appropriate in the next 10 years to eradicate
planted trout from up to 10 percent of lakes containing those trout, but
imprudent to go beyond that goal.
A CalTrout policy statement declares: "A substantial body of research seems to
show that trout and frogs cannot co-exist in the high country lakes where frogs
are native and trout are not. The dilemma is what to do: keep the recreational
fishery or reduce it or eliminate it altogether to save the frogs?"



kathy :-)
A HREF="http://www.onceuponapond.com/"Once upon a pond/A

Ka30P wrote:
Sigh, you can tell this article has me tearing my
too grey hair out. I've been posting about Pacific
tree/chorus frogs not breeding in fish filled lakes
for a couple years now.....
OKAY, this time I'll post the article ;-)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

BERKELEY
Cal biologist solves mystery of disappearing Sierra frogs

David Perlman, Chronicle Science Writer Thursday, May 13, 2004


Sometimes common sense takes alittle longer to become
established in
a well educated mind.

--
Bonnie
NJ