Wandering Western Pond Turtles Turn Up in Muir Woods

Turtle 9, trapped just upstream of Bridge 3 in Muir Woods after many reports from volunteers, staff and visitors. After a routine health check he was released back to the log jam where he was found. Photo: NPS/Carolyn Shoulders.

In 2017, scientists released a group of western pond turtles (Actinemys marmorata) — California's only native freshwater turtle — at Muir Beach Lagoon, part of an effort to restore healthy populations in the species' historical range. Biologists have followed the group ever since, but in the summer of 2023 two of them turned up somewhere nobody expected.

Back from the stew pot

The release was part of the Head Start Project, which is returning native turtles to Golden Gate National Recreation Area. The shy reptiles are a species of special concern in California and vulnerable on the IUCN Red List, and before the project none had been seen in southern Marin County since the 1990s.

Commercial trappers once took them in huge numbers for the turtle soups and stews served in San Francisco's hotels and restaurants — by 1895, an estimated 63,000 had been collected in the Bay Area and Central Valley for the city's meat markets. That demand faded soon afterward, but today urban growth, fragmented habitat and invasive species such as bullfrogs and largemouth bass, which eat young turtles and compete for food, keep populations under pressure.

Aquatic Ecologist Darren Fong removes Turtle 1's old tracking device so he can be fitted with a new one. Turtle 1 was taken back to Muir Beach to keep him clear of construction on the Muir Woods salmonid habitat enhancement project. Photo: NPS/Annie Berlinghieri.

The 2017 turtles spent 1–2 years growing up at the San Francisco Zoo, safe through their most vulnerable stage. Until the year before the sightings, scientists followed them by radio telemetry, and many seemed to be doing well around the lagoon. The most far-ranging one had been found a mile away at Green Gulch Farm.

An unexpected journey

It turned out that turtle was not the boldest. In summer 2023, during the Redwood Creek habitat enhancement project, two males from the 2017 group — now 7 or 8 years old, and nicknamed Turtle 1 and Turtle 9 — were spotted by chance more than three miles upstream, in Muir Woods National Monument. They had probably paddled up the winding creek to the stretch shaded by the monument's redwoods, becoming the first western pond turtles ever recorded there. Volunteers and visitors crowded to see them.

The route of about 5 miles along Redwood Creek that Turtles 1 and 9 probably followed from Muir Beach to Muir Woods. Map: NPS/Matt Millado.

Park biologists set out to catch and measure the travelers:

• Turtle 9 was caught in July and released again in Muir Woods; the team is using radio telemetry to find him again.
• Turtle 1 was caught in August and moved back to Muir Beach, away from the construction. Found there again in September, he was fitted with a GPS tag alongside his radio transmitter.

Turtle 1's GPS tag records his position one to three times a day; here scientists download its data. Photo: NPS/Matt Millado.

Why go upstream?

No one knows yet why the turtles traveled miles up the creek. Biologists suspect they may have been looking for more, or different, resources, but are considering other explanations. The sightings have already taught them something new about how far and how widely the species moves, and the GPS data will show where Turtle 1 goes at different times of year and how he uses different habitats — knowledge that could help protect this vulnerable species.

More

• A record year for western pond turtle reintroductions
• Health checks show growth of reintroduced western pond turtles as tracking project ends
• Redwood Creek habitat restoration at Muir Woods
• Volunteer with the Marin Municipal Water District turtle observer program

Sources

Based on Matt Millado and Avani Fachon, "Wandering Western Pond Turtles Turn Up in Muir Woods," Golden Gate National Recreation Area and San Francisco Bay Area Inventory & Monitoring Network, National Park Service, October 2023; rewritten in hubnx's own words. The source dates the turtle trade's peak to the early 20th century but gives its figure for 1895; this page gives only the 1895 figure.