A first-of-its-kind study demonstrated the spread of the bullfrog takeover in Montana.
The researchers found the invasive species is now thriving and spreading in the Yellowstone River, the U.S. Geological Survey reported.
The bullfrogs are believed to be the responsible for the decline of a number of amphibian and insect populations. The creatures reproduce rapidly and have hug appetites, they have also been known to carry a number of amphibian diseases.
"The impacts of bullfrogs on native amphibians in the Yellowstone River are not yet known, but native Northern leopard frogs are likely to be most vulnerable to bullfrog invasion and spread because their habitats overlap," said Adam Sepulveda, USGS scientist and lead author of the study.
To make their findings the researchers conducted field surveys in 2010, 2012, and 2013. They gathered visual data on adults, egg masses and larvae as well as audio surveys of mating calls.
Bullfrogs are native to North America but were not documented in the Yellowstone region until 1999. These new surveys show bullfrogs are firmly established in the Yellowstone River floodplain and are quickly spreading to new habitats.
In 2010 the bullfrogs' habitat extended from about 37 miles along to Yellowstone River to 66 miles in 2013. The number of breeding sites in the region jumped from 12 sites in 2010 to 45 sites in 2013.
"Bullfrogs were likely introduced to the Yellowstone River region for food, recreational hunting, bait and pest control, and as released pets," said Adam Sepulveda, USGS scientist and lead author of the study.
The study's findings can help land managers focus on prevention, early detection, direct removal, and restoration of the invaded habitats.
The article titled "Invasion of American bullfrogs along the Yellowstone River" was published in a recent edition of the journal Aquatic Invasions.
