Former pets, released in the wild, wreak havoc on native species
Wild turtles are generally shy creatures, prone to plopping into the water and disappearing the moment they catch humans peeping in on their frequent sun-bathing sessions. That wasn’t the case with a massive red-eared slider that naturalist Christine Hood recently encountered while leading a group of kids on a hike along Big Chico Creek.
“It was huge,” Hood said, holding her hands apart to approximate a circle about one-foot in diameter. “And it was bold! Rather than swim away, it just sat there staring at us like it was thinking, ‘Yeah, here I am, so what?’
“It’s taken over that whole area, and I think it knows that. It was unfortunately in a spot [where] we used to have a lot of western pond turtles, but we don’t see many there anymore.”
Hood is an avid hiker, naturalist and educator at the Chico Creek Nature Center who regularly encounters red-eared sliders (commonly abbreviated as RES)—an invasive species native to the southern United States—in Big Chico Creek, Teichert Ponds, the Sacramento River and other local bodies of water.
It’s not usually the turtles’ size she finds overwhelming, but their ever-increasing numbers, a phenomenon she said coincides with an apparent decrease in populations of their smaller, native cousins—western pond turtles.
It’s also a phenomenon that’s become common worldwide. RES are the most common turtles sold at pet stores, and their introduction into the wild has mostly been blamed on people releasing former pets.
“People keep them a little while. Then, for whatever reason, don’t want them or can’t keep them anymore,” said Kevin Thomas, an environmental program manager of fisheries for the state’s Department of Fish and Wildlife, who is based in Rancho Cordova. “They can’t give them back and don’t want to kill them, so in their mind, the best thing to do is to take them to a pond or a creek and let them go.”
Thomas said that’s bad for many reasons, including the fact that releasing animals into the wild is a misdemeanor. Far worse is the damage it can do to local ecosystems.
Part of the reason the turtles are regularly abandoned, according to information from the DFW and other sources, is because they are long-lived (20 years in captivity, 40 in the wild) and can quickly outgrow an owner’s expectations. It is illegal to sell them in the U.S. before they develop a 4-inch carapace (shell) due to an increased risk of transmitting salmonella to people who handle them, but they are commonly sold just above that size and can grow to one-foot in length and diameter.
Native western pond turtles, by comparison, average around an 8-inch carapace when fully grown. The smaller natives can’t compete for food sources and space, Thomas said.
“Sliders are more prolific breeders and reproduce much more,” he explained. A female RES can lay up to six clutches per year, each containing up to 30 eggs, compared to a clutch of 5 to 13 eggs once or twice a year for a western pond female.
“If you put one or two [RES] in a pond filled with western pond turtles, chances are that before too long you’ll have much more red-eared sliders. They’ll eat [the natives] out of their habitat until they either leave or die.
“The situation is pretty ubiquitous across California,” Thomas continued. “Pretty much anywhere you can find turtles, [RES] will be there. If you’re lucky, there might be some western pond turtles left.”
Thomas said a similar problem exists with snapping turtles, though they’re not as common as the sliders. He noted that American bullfrogs—brought to California as a food source, for their legs, in the late 1800s—also wreak havoc on aquatic ecosystems.
Getting rid of the turtles is difficult, Thomas said, as the wildlife department lacks resources and manpower for large-scale eradication efforts; sometimes the DFW will permit outside organizations to conduct such operations.
Turtles can’t be taken for pets from the wild without a permit, but they can be removed for consumption purposes with a sports-fishing license.
“It’s pretty amazing what some people put in the water and we end up finding,” Thomas said as he spoke about an environmental disaster rooted in released pets. He mentioned a 5-foot alligator gar (also native to the South) pulled from the Sacramento River Delta, which hangs stuffed on a wall at the DFW building he works in; super-size goldfish pulled from Lake Tahoe; and the surprisingly common occurrence of South African piranha and their cousins, pacu, in northern California waterways.
“They’re usually dead by the time we find them and the whole man-eating thing is kind of a myth,” Thomas said. “I’ve never heard of them hurting anybody here, but they might be able to bite you, in theory.”