Imported Bullfrogs Responsible For Transfer Of Fungus That Kills Its Western Cousins, Study Suggests

Scientists think they’ve found the reason why amphibian populations across the Western United States are in decline. The culprit: imported American bullfrogs used for food and as pets.

When bullfrogs escape, or are let go, they often carry a fungus called chytrid, says staff scientist Tiffany Yap with the Center for Biological Diversity. When species — such as the endangered mountain yellow-legged frog and the California tiger salamander — encounter infected water, the fungus affects the skin and reproduces itself in it. This disrupts life functions and “leads to an electrolyte imbalance and that eventually leads to heart attack,” Yap said.

Yap led a recent study on determining why the amphibians were dying, published in the journal Plos One, and found that amphibians are at risk across the state.

The bullfrogs in question are native to the Eastern United States. About 2 million live bullfrogs are imported to California every year, “which means we’re constantly putting these local populations of amphibians at risk,” Yap adds.

The researchers found the link by looking at historical records from as far back as the 1800s and compared the timing of bullfrog introduction into the Western U.S. and the emergence of the disease in local amphibian populations. She says this research is important because amphibian health often directly indicates how healthy the environment is.

She says the California Department of Fish and Game Commission needs to act on banning imports of bullfrogs into California. The commission heard a staff presentation on regulatory options in 2017 on how to address impacts on wildlife. Oregon and Montana have already banned bullfrog imports.

“This study really reemphasizes the dangerous threat that bullfrogs pose on our native amphibians,” Yap said. “California just really needs to take a hard look at this issue and address it.”