"One reason American bullfrogs are among the top worst globally introduced pests is because they eat everything—anything that fits into their mouth," said senior author Brian Todd, a UC Davis professor in the Department of Wildlife, Fish and Conservation Biology. "They've been causing declines to native species everywhere they're introduced, which is around the world."

To research a potential link, the authors conducted a seven-year study to examine the impact of removing bullfrogs on native turtle populations. Between 2016 and 2022, they monitored four sites at Yosemite where native turtles persisted—two with bullfrogs and two without.

Where bullfrogs were present, only older, large turtles—too big to fit in bullfrogs' mouths—remained. Researchers even found juvenile turtles—along with newts, snakes, small birds and rodents—in the stomachs of captured bullfrogs. Turtles were up to 36% larger and up to 97% heavier at sites where bullfrogs were present, suggesting younger turtles are not surviving at sites shared with bullfrogs.

We removed 12,317 bullfrogs, larvae, and whole egg masses from one site and 4067 from the other, reaching near complete eradication by 2019. We captured just large adult turtles where bullfrogs were present compared with all sizes where bullfrogs were absent.