After removing 117 invasive red-eared slider turtles from the UC Davis Arboretum, researchers found that the turtle species competed with the endangered native western pond turtles for several resources, including food. 

The study, published Aug. 15 in PeerJ, noted that the western pond turtles gained an average of 40 grams within one year of the red-eared slider turtles being removed  — a 5 to 10 percent increase in body weight, according to a senior author of the study, Gregory Pauly, in a Berkeley News article. This increase in body weight is especially critical for female turtles, whose egg clutch size is related to their overall size, Pauly said in the article. 

Max Lambert, one of the study’s authors and a current postdoctoral fellow at UC Berkeley, said that the western pond turtles — who are in a rapid decline due to agriculture and urbanization — became more relaxed and comfortable after the removal of red-eared slider turtles.  

“This (study) definitely showed that there was some really strong effects,” Lambert said. “Not necessarily that (red-eared sliders) were kind of being mean turtles and pushing the western pond turtles around, but that there were so many sliders that it was just cramped conditions.”

To observe the effects of removing the invasive red-eared slider turtles, Lambert and his fellow researchers — who were undergraduates at UC Davis at the time — spent thousands of hours with the turtles, sometimes jumping into the pond to scoop up stragglers by hand. 

He added that as students, they had unique access to red-eared sliders — one of the most globally invasive species in the world — and a “substantial population” of western pond turtles.  

Moving forward, Lambert said he wants to conduct similar research in the Bay Area. He started the process to gain a permit with the East Bay Regional Park District and said he plans to start survey work on turtles in several small ponds and lakes in the spring of 2020.

Lambert also hopes to tweak some urban pond habitats to give some advantages to the endangered western pond turtles. According to Lambert, something as simple as adding some logs to these habitats can have a significant effect, as basking helps western pond turtles eliminate parasites and digest their food.

Finally, Lambert spoke against having red-eared sliders as pets, adding that they are often released by their owners when they become too large and difficult to handle.

“Red-eared sliders are great little animals, but not really great in the pet trade both for the welfare of those turtles and for conservation,” Lambert said. “I think it’s time for us to really start thinking about banning the sale of this species, and if we’re going to benefit native species, then also actually removing sliders from where they have been introduced.”