A Wellness Check for Tilden Park’s Turtles

November 4, 2021
By: Kara Manke
Tilden Park’s Jewel Lake is home to a community of Western pond turtles, a species that is struggling to survive the combined threats of climate change, habitat loss and competition from red-eared slider turtles. (UC Berkeley video by Roxanne Makasdjian and Jeremy Snowden)

Former UC Berkeley postdoctoral scholar Max Lambert is part of a team of wildlife experts who spent much of the pandemic checking in on the health of the Bay Area’s Western pond turtles, including a population living right next door in Tilden Regional Park.

Despite being California’s only native freshwater turtle, the Western pond turtle is struggling to survive the combined effects of climate change, habitat destruction and urban development — not to mention competition with the larger, more aggressive red-eared slider turtle, an invasive species. The slider turtle, whose characteristic red stripes are said to have inspired the colorful face masks worn by the Teenage Mutant Ninja Turtles, often is purchased as a pet, only to later be released into the wild.

In June 2020, Lambert and the team began a survey of the turtles living in Tilden’s Jewel Lake, periodically setting netted traps baited with canned sardines to safely catch the amphibians, examine their health, and then release them back to into the pond.

On the plus side, the survey suggests that Western pond turtles outnumber invasive red-eared sliders in the lake, and follow-up visits showed that the native turtles were remarkably resilient to the dwindling water supply at Jewel Lake, which dried up completely in fall 2020.

A photo of a Western pond turtle in some grass
The Western pond turtle, characterized by yellow-spotted heads and limbs, is California’s only native freshwater turtle. (Photo courtesy Max Lambert)

“We were curious how many Western Pond Turtles would survive and were delighted that we caught tons of them that we had marked [in 2020],” Lambert said. “This makes sense, given that the species evolved in California’s Mediterranean climate, which naturally has plenty of years where water dries up. The species just knows what to do and goes on land to find cooler places to hang out until the water comes back.”

However, the community of Western pond turtles at Tilden still faces myriad challenges. The team found that male Western pond turtles outnumbered the females, and it only identified a few juvenile turtles, indicating that the species may be struggling to reproduce.

Alarmingly, Lambert also discovered signs that Western pond turtles throughout the Bay Area, including at Jewel Lake, showed signs of infection from a deadly, shell-rotting fungal disease first discovered in Washington state.

“The fungus literally rots the shell while the turtle is alive. It’s analogous to having a fungal infection on your fingernail that works its way to your rib cage and spine,” Lambert said. “We haven’t done the molecular test yet, but there were some pretty nasty signs of shell disease at Jewel Lake. The edges of some turtles’ shells were just crumbling to pieces, and the belly of one turtle’s shell was as pliable as oversteamed broccoli.”

Lambert, who is now an aquatic research manager with the Washington Department of Fish and Wildlife, said that biologists with the East Bay Regional Park District and the San Francisco Zoo will continue to keep a close eye on Tilden’s turtles. The team recently published a study in the journal BioOne describing its discovery of the turtle shell fungal disease in Bay Area Western pond turtles.

A photo showing a close-up of two red-eared slider turtles.
The red-eared slider turtle, whose red head stripes are said to have inspired the colorful face masks worn by the Teenage Mutant Ninja Turtles, are often purchased as pets and later released into the wild. (Photo courtesy Max Lambert)