Naturalists search for area's disappearing toads

Posted: Tuesday, October 07, 2003

Bob Armstrong remembers the days when toads were common at the Dredge Lake area, between Back Loop Road and Mendenhall Lake.

"It was so thick you could hardly walk without stepping on them," the longtime outdoorsman and naturalist said. "Almost anyplace you'd go in the Juneau area, you'd run across them."

But over the past 30 to 40 years, the number of toads has dropped to levels so low it's taken a concerted effort to find the ones that remain.

Funded by the Alaska Department of Fish and Game and working with the Juneau-based nature education group Discovery Southeast, Armstrong and other naturalists and volunteers have been studying local amphibians on and off for the past two years, hiking up ridges, wading into beaver ponds and squatting next to gravel-road ruts. After examining 150 ponds, including detailed study of 42 within a half-mile of Juneau's road system, they've found seven with breeding populations of native toads, plus hints of three more.

Whatever is killing off Juneau's toads could be part of a global trend threatening amphibian populations. The cause could be a combination of factors including pollution, global warming, a type of fungus and changes in the ozone layer, said ecologist Mary Willson, who is involved in the study.

"There's a big controversy about what's causing this in different places," Willson said. "There may be a predisposing factor such as pollution and pesticide runoff into the water and that impairs the immune system. Something weakens them and then they get slammed."

The toad hunters found a few areas with frogs and newts that could be introduced species and, as such, could carry diseases or compete for food and habitat.

A tree frog, which normally lives no closer than Washington state, turned up in one Valley neighborhood, methodically and unsuccessfully calling for a mate. Researchers also found what looked like red-legged frogs in a different part of the Valley. They worried the frogs could be invasive, but the species turned out to be native to Taku River and thus not very threatening, said naturalist Richard Carstensen.

Introduction of non-native species by pet owners, including people who import frogs as food for pet snakes, is a problem, the researchers said. Carstensen urged anyone with pet frogs, toads or other amphibians to keep them at home or destroy them rather than let them free.

Equally important is the need to leave native species where they are, one of the reasons the researchers are not divulging the locations of any of the amphibians they found.

"Tadpoles should not be collected for classes or for kids to have in aquariums," said Willson. "These things are in such trouble, they should be left utterly alone."

Carstensen is compiling the data for submission this fall to Fish and Game, and a public presentation will follow. The results will show some hard-science findings that will be of use in future studies.

For example, frogs and toads like marshy areas called fens, which are less acidic than bogs, although the issue may be food, not pH. They move more and are easier to spot when the temperature is warm.

But the big question - why the once-common amphibians have almost disappeared - remains an item of conjecture.

Carstensen said the prevalent theory is fungal infections appear to have affected populations of frogs in Australia and the American tropics.

The type of fungus called chytrids occurs naturally in forests.

"It's a fungus that commonly breaks down plant material," Armstrong said. "It appears that during the warmer winters we're been having, this fungus is becoming more active and the toads' defenses when they're in their hibernation mode could be pretty low. It's possible it's attacking the toads."

While their study is not likely to present clear conclusions about the fungus or another cause of amphibian decline, it will help with future research, Armstrong said.

"Since we don't have any good baseline data to compare it to, it's really difficult to say at this point whether they're going to come back," he said. "My intuition is to say they appear to be extremely fragile."



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