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Amphibian Decline

Tuesday, April 22, 2003 at 3:29 PM

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For more than a decade, scientists the world over have been concerned about what appears to be a global decline in the number of frogs, toads and other amphibious species. It's not clear what's behind the loss of population and finding those answers may be complex. Scientists suspect there may be a number of different factors at work in each instance where declines have been documented. In order to discover what those factors are, researchers need to study how a given population behaves over a period of time. But there are surprisingly few such studies underway in the U.S. ideastream's Karen Schaefer takes us to one such project in Summit County, where a biologist and his students from the University of Akron are studying spotted salamanders.

About two dozen Bath Township residents - adults and children - have gathered on a cool spring evening in the Steiner Woods Nature Preserve, about 25 miles southeast of Cleveland. They’re accompanied by Dr. Peter Niewiarowski, a biologist from the University of Akron. For the last five seasons, Niewiarowski and his students have been coming to this 23-acre woodland to study a large population of yellow-spotted salamanders. Each spring, a biological urge drives thousands of these creatures to lay their eggs in farm ponds and vernal pools. Niewiarowski has taken advantage of this behavior to get a closer look at these normally hard-to-find amphibians.

Peter Niewiarowski: This pond is home to lots of amphibian species, including spotted salamanders. They get pretty big - 5, 6, maybe 7-inches. They’re black and they’ve got bright yellow spots on their backs.

Around the pond Niewiarowski and his students have erected what he calls a drift fence, a solid metal edging about two feet high that completely encircles the water. So when they get to the pond to breed, the salamanders can’t get in.

Peter Niewiarowski: What happens is they hit the fence and they get a little bruise on their nose - that’s supposed to be a joke. (laughter) And then they walk left or right and every 30 feet or so, there is a bucket - see one right there - there’s a 5-gallon bucket that’s sunk in the ground. So when they get to one of these buckets, they basically just fall in.

Niewiarowski says last year on a night much like this one, but pouring with rain, more than 1,600 salamanders fell into the buckets on a single evening.

Peter Niewiarowski: So what we do then is we collect all these animals, we take data on where they came in, we bring them back to the lab. And then we collect a bunch of information on them, like, how many, how big, how many males, how many females, how many we’ve seen before. And we can tell those kinds of things, because we mark every individual salamander with an identifying mark. Gathering all that information allows us to estimate the health and status of the population. And therein lies an issue that a lot of scientists are talking about. Has anyone heard of amphibian decline?

Niewiarowski estimates that more than 7,000 salamanders live around this small pond. In fact, since he and his students began their long-term demographic study of the common spotted salamander, the population here appears to have actually increased.

But for the last decade, scientists around the world have been documenting alarming declines in the size and number of amphibious species.

Peter Niewiarowski: And it turns out that you really can’t say it’s happening or not - or why it’s happening - unless you have data like the kind I just talked about.

Niewiarowski’s work is funded in part by a grant from the National Science Foundation. Surprisingly few such long-term studies are being undertaken. In 2000, Congress voted funding for a national project to study amphibian decline. Walt Sadinsky is a biologist with the U.S. Geological Survey in Wisconsin.

Walt Sadinsky: The trick is that we have to approach a particular population in terms of the local context of what it is in fact exposed to, to understand how those factors may or may not be impacting that population.

In other words, each incidence of decline may be the result of a different set of factors. Sadinsky says conditions favoring decline could range from global warming to reduced water quality to loss of habitat. In Ohio, he says the loss of isolated wetlands to agriculture and urban sprawl is one potential problem. At Steiner Woods, University of Akron graduate student Jennifer Purrenhage is trying to find out whether animals are moving between isolated breeding ponds and pools.

Jennifer Purrenhage: Each year, they’ve noticed that more than half of the salamanders are unmarked, which means we’ve never seen them before. One explanation is that they’re coming from somewhere else.

Purrenhage is sampling salamander DNA from animals in about 30 ponds over a 40-square-kilometer area around Steiner Woods to see if populations share any characteristic markers. Shared markers will tell Purrenhage if salamanders are adapting to habitat loss by moving longer distances to breed.

Walt Sadinsky: This sort of information will be enormously useful to the folks there who have some control over what happens with that habitat in which they live.

Walt Sadinsky of the U.S. Geological Survey believes the Ohio study and similar projects in Missouri and Minnesota will help in the effort to understand the causes of Midwestern amphibian decline. But he says to counter-act those effects, localized data will be crucial. So Peter Niewiarowski and his students plan to continue their long-term study of salamanders. And they’ll refine their data with research projects on other Northeast Ohio amphibians. In Bath Township, Summit County, Karen Schaefer, 90.3.

Additional Information

* U.S. Geological Survey, Upper Midwest Center for Environmental Science
* Worldwatch Institute - Deciphering Amphibian Decline: New Approach to Science Needed

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