If you wander around California’s streams or ponds, you’re likely to spot a turtle trundling along the water’s surface. If you’re lucky, this animal is a western pond turtle, because not only are western pond turtles an exquisitely marbled reptile, but they are also one of California’s most imperiled species. Pond turtles have a relatively large natural range, extending throughout Western North America from British Columbia down to Baja California. But everything from climate change to a dramatic loss of habitat has dealt pond turtles a serious blow. During the California Gold Rush, people even used to eat pond turtles in large numbers and less than a century ago, you could buy a dozen wild pond turtles in San Francisco markets.
Western pond turtles are in such rough shape that they are under review for listing as “endangered” under the United States Endangered Species Act. Chances are, however, if you’re in a city or suburb, the animal you will see is a red eared slider turtle. Distinguished by a red stripe next to their eyes, sliders are very distinctive. Red-eared sliders are also common across California, but they are native to the central and Eastern United States. Additionally, because they are so common in the pet trade, sliders have been distributed in abundance throughout the rest of the United States and across the world. The problem is that red-eared sliders get big and mean in a short amount of time, which causes people to release their red-eared pets into the wild rather than finding them another home.
Pet sliders have been released in mass droves not only throughout California, but on every continent except Antarctica. Conservation biologists have been concerned for several decades as to whether or not feral slider turtles compete with native turtles for food and space in their habitats. Until recently, we had no evidence from wild populations that invasive sliders might impact native turtles anywhere. My colleagues and I recently published a study where we removed the majority of a red-eared slider population from a shared habitat — an incredible 177 sliders totaling over 200 pounds of turtle mass. Removing this slider population allowed native pond turtles to access more food and habitat space. Interestingly, we also found that so many pet sliders had been released into this habitat that the sliders were also impacting each other. This result showed that not only do released sliders pose a threat to native turtle conservation, but they also pose a threat to themselves.
Cities and suburbs can be rough places for California’s western pond turtles. Urban areas are feral slider hot spots. Because most invasive red-eared slider turtles are released pets, the slider invasion is concentrated in lakes, ponds and streams where people live. Red-eared sliders are not, however, the only problem facing urban pond turtles. Roads fracture the landscape and make it harder for pond turtles to move between habitats, and plenty of turtles get smashed by vehicles. This issue is often worse for females, which have to travel farther on land to find places to nest. Urban areas are also home to fierce predators, such as coyotes and raccoons, which dig up turtle nests and eat adult turtles. Beyond invasive competitors and lethal encounters, western pond turtles are timid animals and get stressed out when they see walkers, joggers or bikers. This causes them to abandon their habitat unlike sliders. Nevertheless, urban areas don’t have to be lost causes for imperiled pond turtles. In fact, cities and suburbs can be home to strong western pond turtle populations and may be exciting places to focus on pond turtle conservation.
Our study provides pretty clear evidence that removing red-eared sliders can be an important part of pond turtle conservation, particularly in sensitive urban habitats. Removing sliders from habitats is, however, only a temporary solution. We must ban the sale of pet sliders to prevent them from being released into the wild. As our study shows, releasing sliders into the wild hurts both native turtles and pet sliders. Therefore, banning the sale of red-eared sliders will benefit pond turtles and sliders. Urban bodies of water can offer some relief from hot weather and droughts that will only get worse with climate change. We can also tweak urban habitats to favor pond turtles by adding more floating spaces, providing cover from people and minimizing the distance turtles must travel to nest. Urban habitats will always pose challenges for pond turtles, but they can also be part of a holistic effort to protect this Californian species. Conserving western pond turtles is going to take some serious work, but it’s worth it. Unlike the rest of the country, California doesn’t have an abundance of native freshwater turtle species. Therefore, protecting the western pond turtle means protecting an iconic piece of California’s natural history.
Max Lambert is a postdoctoral research scientist in the department of environmental science, policy and management at UC Berkeley.