Researchers at the University of California, Davis monitored the turtle populations from 2016 to 2022 at two sites in the park that also have bullfrogs present and two sites where the bullfrogs are not present.
The American bullfrog (Rana catesbeiana) is an invasive species in Yosemite National Park, and they have eating the juvenile native Northwestern pond turtles (Actinemys marmorata) in the park, according to a study on the effects invasive bullfrogs have on the turtle populations in the park.
Researchers at the University of California, Davis monitored the turtle populations from 2016 to 2022 at two sites in the park that also have bullfrogs present and two sites where the bullfrogs are not present. The researchers removed 12,317 bullfrogs, larvae, and whole egg masses from one site and 4,067 bullfrogs from the other site and completely removed all of the amphibians by 2019. At the sites, they captured large adult turtles where the bullfrogs were present and all life stage sizes of the turtles at the sites where the bullfrogs were not present.
American bullfrog. Photo by M. L. Haen/Shutterstock
Before the complete eradication of the bullfrogs at these sites, the researchers found juvenile turtles inside the stomachs of the bullfrogs. Cohabitating with the bullfrogs caused the turtles to grow 26 to 36 percent larger and 76 to 97 percent heavier than at the sites where the bullfrogs were absent.
Western Pond Turtles in Washington Rebound From Brink of Extinction
The study showed that there was a lack of juvenile recruitment where the invasive bullfrogs were present and instituting a control on the amphibians could assist in recovering turtle populations by easing the predation of pond turtle hatchlings and juveniles. The eradication of the bullfrogs may be necessary to ensure that these native turtles persist.
The complete study, “Effects of invasive American bullfrogs and their removal on Northwestern pond turtles,” can be read on the Biological Conservation website.
Western Pond Turtle Information
The western pond turtle (Actinemys marmorata) is native to California and much of the West Coast of the United States. Listed as vulnerable by the IUCN, the western pond turtle is an omnivore, subsisting on insects, crayfish and other aquatic invertebrates as well as plant matter. They are also known to eat fish, tadpoles and dead animal matter.
American Bullfrog Information
American bullfrogs (Rana catesbeiana) are the largest native frogs in North America. Growing to about 8 inches in length, the American bullfrog is large, strong, and overall just a beast of a frog. These frogs are great swimmers with big webbed feet, and are voracious eaters, capable of eating almost anything that they can fit into their mouths. The frog is found throughout much of the United States, naturally in 36 states, and is found in many places where it is an invasive species.
