Pesticides Used In California’s Central Valley Killing Frog Populations in Nearby Sierras
Scientists have determined the chemicals that make the Central Valley a rich agricultural region are responsible for frog deaths and tadpole abnormalities in the Sierra Nevada Mountains.
Just when it seems things can’t get much worse for our cold-blooded friends, researchers have added pesticides to the growing list of causes (such as habitat loss and chytrid fungus) for the massive worldwide decline in amphibian populations.
An article in today’s Central Valley Business Times says that zoologist Don Sparling and his team are continuing to build up a body of evidence that shows neurotoxin pesticides are making their way out of the valley’s farms and into the snow and streams where the frogs live and breed - with catastrophic consequences.
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The study, focusing on foothill yellow-legged frogs (Rana boylii) and tiny Pacific tree frogs (Hyla regilla), found that both native species were declining in the Sierras at an alarming rate. The Central Valley - a 400-mile long agricultural area - grows a multitude of crops, such as almonds, peaches, grapes, tomatoes, oranges, pistachios and is bordered by the Sierra Nevada mountain range.
Unfortunately, the chemicals used to produce this agricultural bounty are also killing the frogs.
Sparling, an associate professor of zoology at Southern Illinois University Carbondale, has been studying this issue for years - and the evidence continues to grow. His earlier study, Pesticides and Amphibian Population Declines in California, appeared in the SETAC Journal Environmental Toxicology and Chemistry in July 2001. Next year, the second edition of his textbook Ecotoxicology of Amphibians and Reptiles is expected to be out.
Several species of anuran amphibians have undergone drastic population declines in the western United States over the last 10 to 15 years. In California, the most severe declines are in the Sierra Mountains east of the Central Valley and downwind of the intensely agricultural San Joaquin Valley. In contrast, coastal and more northern populations across from the less agrarian Sacramento Valley are stable or declining less precipitously.
But how are the chemicals getting from the valley up into the Sierras?
Sparling’s team used sampling techniques and found that there are two major methods for the pesticides to contaminate the frogs’ habitat.
- Wind. Pesticides are sprayed from airplanes. Not only does the wind blow the chemicals as they are sprayed, but after application, the chemicals “turn into a gaseous state” which is picked up by the wind and spread to the mountains.
- Timing. In the late winter and early spring, chemicals are applied to the region, and these make their way into the snows of the mountains. Tragically, the snow melt coincides with the start of the frogs’ breeding season.
In addition to the adult frogs, vulnerable tadpoles are exposed to the chemicals, causing developmental problems, such as drastic changes in growth rates. Sparling also noted an abnormality that causes the tadpoles’ tails to develop off-center. This renders the animal incapable of swimming normally - they can only swim in a “corkscrew” pattern - resulting in heavy predation of the tadpoles.
Chemicals such as endosulfans kill by overloading the nervous system so that the animal cannot use its breathing muscles. Foothill yellow-legged frogs are particularly vulnerable to these chemicals. Professor Sparling said its use as a pesticide is banned in Europe and Australia - yet the U.S. Environmental Protection Agency is still “studying” the issue.
Can large-scale farming and environmental protection co-exist? Sparling thinks they can.
To produce crops to provide for the world we have to use pesticides, and I’m not anti-pesticide. But it’s important for us as scientists, agriculturalists and environmental protectors to make sure we continue developing pesticides that are as protective as possible of non-target animals as can be, both in the chemicals we use and application methods.
Like other scientists, Sparling believes that studying the health of frog populations is critical for learning how to protect the environment.
Frogs are like the canary in the coal mine. They serve as early alarms for the environment. They also provide a large and important link between the aquatic and terrestrial environments. If amphibians go, a huge link will be gone.
As a lifelong California resident, I can’t imagine cold spring nights without the call of the little Hyla regilla. Let’s hope these studies lead to a frog-friendly solution for growing healthy crops.
Image source: http://www.flickr.com/photos/miguelvieira/ / CC BY 2.0
Well, not being a “scientist” I don’t see it as “we must ensure that insecticides do as little harm as possible to non-target species”, but rather “If the colateral is unsustainably bad then the stuff with not have to be PRODUCED !!”
No insecticide means get natural predators in. But who in their comfy, air-conditioned, office wants to get their hands dirty like that - get real !
No herbicide, means people/machines with hoes to do-in the weeds.
So where are the “Green job creationists” at this time ? They are out in force when it comes to “building and maintaining windfarms” - which, during their entire lifespan, provide only a small fraction of the energy required to build a replacement.
Also, maybe the training required, to get the average delinquent doing “community service”, to be able to tell the difference between a this and a that is just too expensive. But “maintaining” a hulk of window-dressing, yes, they’re “technically competant” at that. Give me hope, Johanna !!
From the author:
Thank you for your comment. I agree, I also found the scientist’s view of pesticides and non-target species to be troubling. Intriguing idea for community service, btw.