Strong red tide may leave lasting impression on turtle populations

Chad Gillis
The News-Press

A particularly strong red tide has killed hundreds of sea turtles in Southwest Florida over the past nine months, and researchers say the toll could hurt the area's sea turtle population for decades. 

The red tide started in October but has become much more intense since June. 

"I think that we will be feeling the result of this for decades to come," said Heather Barron, a red tide expert and director of the animal hospital at the Center for the Rehabilitation of Wildlife on Sanibel. "There’s a possibility that we will have fewer nesting sea turtles in our waters in the coming year. ... A lot of the turtles that normally would be nesting here have died." 

Barron is one of the world's top researchers when it comes to red tide effects on animals and humans. She's published numerous scientific papers on the subject and has developed methods for treating red tide victims. 

Jack Brzoza, a sea turtle technician for the Sanibel Captiva Conservation Foundation, measures the carapace of a dead loggerhead sea turtle on Sanibel Island while Rick Bartleson, a water quality scientist for the SCCF, takes notes. A large number of sea turtles are washing up on Sanibel and Captiva beaches. The suspected cause is red tide poisoning.

Red tide typically runs from October until January or February, when cold fronts from the mainland scatter the blooms and suppress their growth. 

That schedule means nesting turtles aren't often affected because nesting season runs from May through October. 

"Normally we don’t see these big guys with red tide poisoning; they’re coming in to nearshore waters to mate and lay their eggs, and they’re getting exposed," Barron said. 

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Loggerheads are the most common nesting turtle along the Southwest Florida coast, and adults stay close to shore in summer months. 

The smaller Kemp's ridleys have also been showing up dead in large numbers. 

Both species feed on crabs, mollusks, shellfish and other filter feeders, which accumulate the toxin in their systems. 

"It’s extremely sad because the Kemp's ridley is the most endangered of the sea turtles," said Eve Haverfield, with Turtle Time. "Seeing them being affected like this is really, really heartbreaking."

Turtle Time monitors several local beaches during nesting season. 

Haverfield said the early part of nesting season has been relatively successful and that some beaches actually saw an increase in the number of nests compared to last year. 

"In the near future I certainly expect there to be a decrease in the nesting numbers, which is really a shame," Haverfield said. 

The hatchlings, she said, aren't affected by the red tide once they get off the beaches, and the tiny turtles swim desperately for a day or more. 

Hatchlings don't eat for their first few days, so they're not ingesting filter feeders full of the toxin. 

"When they emerge from the nest they’re full of the yolk, and that will be absorbed, and that will keep them fed for a number of days," Haverfield said. "Once they enter the Gulf they are really intent on getting offshore. And they swim about 1 mile per hour, and they’re about 24 miles offshore after a day."

The hatchlings may breathe in airborne toxins, but the hope is that they make it to the seaweed line about 30 miles offshore before succumbing to red tide. 

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"They’re kind of protected from this outbreak, and this is a good thing because it will take 30 to 50 years for them to reach maturity," Haverfield said of loggerheads, the primary species in this region. "One to 4 out of 1,000 survive, and many are eaten by fish. Maybe there are fewer fish out there eating the hatchlings, so perhaps more will survive. I’m kind of hoping for that." 

Barron said she believes the hatchlings are surviving. 

The combination of the yolk and the instinct to swim straight offshore may be saving future generations. 

"They kind of come with a ready-made snack that will keep them going for a few days, and during that time they’re going to swim as fast as they can to the sargassum," Barron said. " And that can be 20 to 30 miles offshore and hopefully outside of the red tide zone."

Florida Fish and Wildlife Conservation records show that more than 700 stranded and dead sea turtles have washed up on Southwest Florida beaches and shorelines since November. 

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If there is any silver lining to this situation, it may be that red tide occurs naturally, so the sea turtles would have faced this even if humans weren't affecting local waters, said Allen Foley, an FWC sea turtle expert.

"There will be some impacts because some adults have died," Foley said. "But like hurricanes, red tides occurred before Europeans came to the New World, so it’s a natural mortality factor." 

When asked about nutrients flowing off the landscape that can feed a red tide, Foley said, "the bloom initiated offshore and was not started by us, but there is the thought that it may spread inshore" because of nutrients. 

So what can the state do to help sea turtles? 

"There’s nothing to do other than going out and catching sea turtles, and that’s logistically impossible," Foley said. 

Connect with this reporter: Chad Gillis on Twitter. 

A large number of sea turtles are washing up on Southwest Florida beaches. It is believed they are succumbing to red tide poisoning. Red tide has been lingering of of Southwest Florida beaches for months. Scientists for the Sanibel Captiva Conservation Foundation are documenting and taking samples for testing from sea turtles found on Sanibel and Captiva.

Turtle facts

-Florida waters are home to five species of sea turtle: loggerhead, Kemp's ridley, green, leatherback and hawksbill. 

-The leatherback is the largest species, with the largest found being 10 feet in length and weighing 2,000 pounds. 

-About 15,000 green sea turtles were shipped annually from Florida and the Caribbean to England to be used for soup during the late 1800s.

-Loggeheads are the most common sea turtle in Florida waters and were named for their big, block-like heads. 

Source: Florida Fish and Wildlife Conservation Commission

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