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Investigating How Red Tide Impacts Sea Turtles

March 6, 2023

As Southwest Florida’s red tide bloom intensifies, the SCCF sea turtle team has seen an uptick in sea turtle strandings, including 6 over the past week.

“Some sea turtle strandings wash up with obvious evidence of vessel strikes, entanglement, or even predation. But during red tide events, when turtles strand with no obvious external injuries, it can be hard to tease out the exact cause of these strandings without further testing,” said Coastal Wildlife Director and Sea Turtle Program Coordinator Kelly Sloan. “However, based on historical stranding reports, we know there tends to be an increase in sick and dead sea turtles washing ashore during intense blooms.”

To report a suspected stranding, please call the SCCF Sea Turtle Hotline at 978-728-3663.

During the extreme red tide bloom of 2018, SCCF documented over 250 sick and dead sea turtles on Sanibel and Captiva. More than 1,200 cases were documented across the region.

“Although the immediate impacts of these blooms on sea turtles are apparent, the long-term impacts of exposure are not as well understood,” Sloan said.

Over the past four years, SCCF researchers have collected nearly 400 blood and hundreds of tissue samples from nesting loggerhead sea turtles and their offspring to examine sublethal health impacts of red tide, including maternal health, reproductive success, embryonic tissues to hatchling pathology, and the transfer of red tide toxins between mother and offspring.

Pepper, the loggerhead pictured here, has had blood collected twice as part of this project in 2020. Both samples revealed extremely low concentrations of red tide toxins.

“The primary route of exposure to red tide toxins for sea turtles is the ingestion of toxic prey,” Sloan explained. “Although Pepper nested during the severe red tide event in 2018, her foraging grounds are not in the Gulf of Mexico, and her prey is likely not contaminated.”

Pepper was last seen on Bonita Beach in July 2022, after which she returned to her foraging grounds in the Caribbean, where she remains now.

The SCCF sea turtle team is analyzing the rest of the data from the study and hopes to have results published later this spring. Collaborators include the Loggerhead Marinelife Center, Florida Wildlife Research Institute, University of Florida, Fishhead Labs, and the University of Miami.


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