In 2022, Hurricane Ian severely affected most fully aquatic turtle populations on the island through saltwater intrusion from storm-surge overwash.

After the hurricane, visual encounters with native species, including live peninsula cooters (P. peninsularis), Florida red-bellied turtles (P. nelsoni), Florida softshell turtles (A. ferox), and Florida snapping turtles (C. serpentina), plummeted.

Storm surges from Hurricanes Helene and Milton in 2024 compounded the high-salinity problem. Salinity is measured in practical salinity units (PSU), with freshwater at <.5 PSU and seawater at about 30 PSU. Most permanent, inland waterbodies still average around 12 PSU.

Despite the increased salinity, over the past four years, one invasive species has been basking, crossing roads, and is commonly seen across most of the island, even near waterbodies with salinities above 15 PSU.

Background on Sliders

The pond slider (Trachemys scripta), native to much of the eastern United States, including northern Florida, is best known by two subspecies: the yellow-bellied slider (T. s. scripta) and the red-eared slider (T. s. elegans), which is pictured above.

“Scientists have documented higher salinity tolerance in other parts of the world, but we have not seen this here until now,” said SCCF Wildlife & Habitat Management Director Chris Lechowicz. “They are survivors. For the last four years, people have been sending us photos of aquatic turtles basking, crossing roads, and laying eggs — most of them are sliders.”

Subspecies are just geographical variations of the same species. Historically, Florida populations were limited to yellow-bellied sliders as far south as the Gainesville area. The red-eared slider range extends relatively close to the western panhandle, so sliders in that area show the influence of both subspecies.

The red-eared slider, native primarily to the Midwest, was the most farmed and sold pet turtle throughout the U.S. from the 1950s-1970s, and remains widely sold worldwide today.

“They were sold as hatchlings throughout the country when they were bright green, with a red bar on the sides of their faces. Unfortunately, people considered them cheap, disposable pets at the time,” said Lechowicz.

However, they eventually grow to 5 to 11 inches long after several years and lose a lot of their attractive coloring. Many people could not house a turtle of this size long-term and ended up releasing them into the natural environment, not just in North America, but around the world, where they are still a problem for native species.

In 1975, the USDA passed a law making it illegal to sell turtles under 4 inches long in the U.S. to thwart salmonella outbreaks from turtles due to poor care. Since then, turtle farms still export millions of hatchlings overseas but must raise them to 4 inches in the U.S. for sale.

“Sliders are highly adaptable and can withstand many temperature gradients and habitats, which is why they are known as the most invasive turtle species known,” said Lechowicz. “Many states have banned their possession due to their invasive capability, including Florida, which has banned red-eared sliders.”

Slider Introduction to Sanibel

On Sanibel, as many as sixteen yellow-bellied sliders were introduced in 1963 by a couple of graduate students on a reptile collecting trip. Even though they are native to Florida, they are not native to central or south Florida.

The red-eared slider was first documented in 1975 from released pet turtles, but they likely arrived earlier.

These turtles spread throughout the island, producing offspring that resemble each subspecies or a mixture of both. After examining more than 100 of these on the island, Lechowicz says most examples show a stronger influence of yellow-bellied sliders.

“Although the other fully aquatic turtle species are still here in small numbers, it will take time without storm surges for deeper wetlands to decrease salinity so the native species can expand their ranges,” he said.

Please report sightings of aquatic turtles to clechowicz@sccf.org.