Increasing reports of deformed frogs and toads in the mid 90s, prompted Congress to mandate studies to look into the problem.
Amphibians are sort of the canary in the coal mine for gauging the environmental health of land and surface water. The study was released in November, and looks at amphibian abnormalities on 152 wildlife refuges across the country, including five in Alaska.
The decade long study by the U.S. Fish and Wildlife Service examined more than 68,000 frogs and toads. Generally, only about 2 percent of the amphibians were found to have abnormal limbs. But there were a few areas, called ‘hot spots’ where the rates were much higher.
Two of those areas were in Southcentral and Eastern Alaska. Mari Reeves is an ecologist with the fish and wildlife service. She says they wanted to see if the hot spots had something to do with people.
“And we found a strong and significant association between abnormalities and road proximity, so if you lived closer to a road you were more likely to be abnormal,” Reeves said. “And it was a probabilistic thing, meaning that if you lived next to a road you were not always abnormal, like we definitely had collection events right next to roads that we didn’t find any abnormal frogs but what we found is that the average frequency went up.”
The abnormal frogs were found in greatest numbers in the Kenai and Tetlan refuge areas.
ANWR, Innoko,Yukon Delta, and the other refuges that were sampled had much lower rates.
Reeves says the connection to abnormal frogs and toads could in part, be linked to copper in brake linings. When you hit the brakes, a bit of the copper grinds off the brake lining and settles on a roadway. Reeves say incredibly low amounts of copper can impact a tadpole’s ability to avoid predators and dragonfly larvae like to eat tadpole limbs.
If they bite them off during the tadpole’s early growth, they can grow back, but they might not look the same.
“And depending on the complexity of how that wound happens, you can get some really interesting malformations like split limbs or limbs that, they’re called bony triangles, in the limb and if it’s just a clean break, you might just get one limb that looks like a normal limb except that it’s smaller than the other ones,” Reeves said. “Those are the really common abnormality types.”
Reeves says another fairly common abnormality specific to Alaska frogs is one called “Black eye” or “Hollow eye,” where the normal gold color around the iris is gone. Researchers don’t know if the frogs can still see through that eye. Reeves says ‘legacy toxins’ were another problem for frogs. Pesticides such as Lyndane, used to kill spruce bark beetles or contaminants that drift to northern climates from other places and drop in snowfall cause toxin accumulation through global distillation. Reeves says multiple stressors likely caused the hot spots for abnormalities.
“We think that we understand at least a bit of how that mechanism works, is that very low levels of contaminants can make the tadpoles sick, can make the tadpoles not as well able to get away from their predator, who bites the legs off and so you get these limb abnormalities,” Reeves said.
She says the study is the largest data set in the world on this amphibian issue, although the testing was only conducted on wildlife refuges.
- Trends in Amphibian Occupancy in the United States (PDF)
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Road Proximity Increases Risk of Skeletal Abnormalities in Wood Frogs from National Wildlife Refuges in Alaska (PDF)
Lori Townsend is the news director and senior host for Alaska Public Media. You can send her news tips and program ideas for Talk of Alaska and Alaska Insight at ltownsend@alaskapublic.org or call 907-550-8452.
