Eradication effort underway on Cache Creek of invasive species

Carlos Guerrero

April 27

There will be a lot less croaking at the Cache Creek Nature Preserve after the first of what could be a years-long effort to remove invasive species.

An eradication effort for bullfrogs and red-eared slider turtles began earlier this month with a second capture effort planned for May, led by Endemic Environmental, a Yuba City-based company that helps nonprofits and others remove invasive species to increase biodiversity.

Endemic Environmental went to work on April 9 and 11, setting and collecting traps for slider turtles and bullfrogs in the wetland habitat of the 130-acre nature preserve, located about 10 miles west of Woodland.

Turtle traps were set during the day, while bullfrogs were hunted at night. Nature Preserve staff were also given training so they can continue the work.

About 18 turtle traps were baited and deployed on April 9 and 10, including the four traps that were built by an Eagle Scout for the Preserve.

In total, almost 50 bullfrogs and about 25 red‐eared sliders were removed from the wetlands, according to Preserve staff. Four western pond turtles were also found in the turtle traps. They were tagged and safely released.

Bullfrogs are much larger than common frogs and eat everything from fish to small birds. Red-eared sliders can be identified by a red splotch on the side of their head as well as brown-yellowish markings on the underside of their shell. They grow more quickly than native turtles and compete for the same foods as western pond turtles. They is considered one of the 100 most invasive species in the world.

A tub of turtles captured by Endemic Environmental staff are removed from the pond of the Cache Creek Nature Preserve. Any western pond turtles that were also trapped were returned as they are native to the region. (Lynne Haralson/Courtesy)

A large red-eared slider turtle is captured for removal from the pond of the Cache Creek Nature Preserve by staff with Endemic Environmental. The turtles and bullfrogs are considered invasive species, which damage the environment by crowding out native turtles and frogs. (Lynne Haralson/Courtesy)

Cache Creek Nature Preserve biologist Felica Wang returns a native western pond turtle to the pond at the Nature Preserve after it was captured along with invasive red-eared slider turtles. (Lynne Haralson/Courtesy)

Neither the sliders or bullfrogs are native to either California or the Cache Creek area. The turtles can be commonly found in pet stores and are usually "small," measuring only a few inches when they are sold. However, as the turtles get larger, they are usually released into the wild where they can grow to more than a foot in length.

In December 2023, California began taking steps to ban the importation and sale of bullfrogs, halting century-old commerce that has introduced deadly disease to the state's native frogs.

The fat, aggressive and often disease-carrying frog, with a basso "jug-o'-rum" call, is native to the eastern U.S. but is raised for commerce in frog farms in China, Taiwan, Brazil and other countries. Every year, an estimated two million live bullfrogs are shipped into California for use as food.

Bullfrogs carry a chytrid fungus called Batrachochytrium dendrobatid, which is contributing to the decline of native frog species. While bullfrogs carry the fungus, they do not die from it. The fungus breeds in the water of their holding tanks and spreads if released into the environment.

The decision by the state to eliminate the frogs ends a battle over animals that are traditional cuisine in Asian communities, will take time to implement.

Millions of bullfrogs live in ditches, canals and ponds across California. They are vexing trespassers. Even as California spends large sums of money to protect populations of threatened native frogs, such as yellow-legged and red-legged species, bullfrogs are devouring and displacing them.

While no one expects to completely eradicate the frogs anytime soon locally, it's hoped that by decreasing their numbers, it will then become easier to find their egg masses and get rid of those as well.

In 2005, the National Park Service began bullfrog removal, targeting various life stages using hand, net, and spear techniques in Yosemite Valley that ultimately removed more than 86% of all bullfrogs and, by the end of 2019, had nearly eliminated them.

The turtle and bullfrog eradication effort is separate from a "small mammal trapping" study also underway at the Preserve.

Held April 7 and 8, in collaboration with UC Davis doctoral candidate Francesca Rubino, seven past and current Nature Preserve wildlife interns and four of Francesca's undergraduate students assisted with file work to trap, tag and release mice and voles.

The traps were deployed in the south section of the grasslands, which was selected because it is the site of a Swainson's Hawk easement. The mice and voles are a common food source for the raptors. There is also a small mammal camera located in the area, which provides information on the types of mammals nearby.

On April 7, 120 traps were deployed. On April 8, the traps were checked early in the morning. Ten traps were triggered, resulting in five house mice, three deer mice, one vole, and one harvest mouse being captured.

The rodents were ear-tagged, sexed and then safely released.

Plans are being coordinated to continue trapping in May.

The Bay Area News Group contributed to this report.