Hundreds of sea turtles washing up dead on SWFL beaches; red tide likely killer

Chad Gillis | Naples

Show Caption Hide Caption Dead sea turtles washing up on Southwest Florida beaches including Sanibel and Captiva Scientists are saying this is worst red tide bloom since 2006. Dead sea turtles washing up on Southwest Florida beaches

Hundreds of sea turtles have washed up on Southwest Florida beaches this year in a mass mortality event that researchers say will impact the recovery of protected species.

Seventeen have been recovered in Sanibel and Captiva waters in the past week.

"Our average for the entire year is usually around 30 or 35, but we’ve had 53 in June and July alone," said Kelly Sloan, a sea turtle researcher at the Sanibel-Captiva Conservation Foundation on Sanibel.

Sloan said SCCF has picked up 91 sea turtles on the islands since the red tide bloom started in October.

"Most of them have been mature adults, and only 1 in 1,000 make it to adulthood," Sloan said. "It takes a loggerhead 25 to 30 years to mature, so that really does have a significant impact on their recovery."

More than 100 turtles have been plucked from Sarasota County waters, and another 66 have been found in Collier.

"It’s really disheartening to see this mass mortality," Sloan said. "This is the 10th month of the red tide event, and it’s the longest continued bloom since 2006."

Previous coverage: Dead fish seen on Collier beaches as red tide persists

Previous coverage: Red tide bloom killing fish, sea turtles in Fort Myers area

Researchers don't know for sure if red tide killed or injured the turtles, but Sloan said she is "very confident" that the turtles were claimed by the algae bloom because many exhibited neurological symptoms associated with red tide.

The bloom has varied in intensity and distribution, at times stretching from the Tampa Bay area to the Florida Keys.

Recent numbers in Lee County have run the gamut, from background concentrations to 1 million cells per liter and higher.

Fish kills and breathing problems in humans can start when levels reach 10,000 cells per liter, according to the Florida Fish and Wildlife Conservation Commission.

Although blooms typically start off Sarasota, this bloom has been centered in northern Lee.

An introduction to red tide Red tide is a harmful algal blooms that can sicken or even kill local wildlife. It also causes respiratory issues in humans and other animals.

The organism that causes red tide here (Karenia brevis) occurs naturally, but many water quality scientists say the blooms last longer and are more intense due to human activities like farming and development.

Collier is seeing above-average numbers of sick and dead sea turtles as well.

"The last two days have been really bad with red tide, and we had two strandings today and two yesterday," said Maura Kraus, a sea turtle expert for Collier County. "The red tide is in everything they eat and they’re breathing it. The most vulnerable turtles are the Kemp's ridleys and the loggerheads, and it's concentrated in the food they eat."

Kemps' ridleys are one of the world's most endangered sea turtles. The loggerhead population here is listed as threatened under the Endangered Species Act.

Strong onshore winds have been blowing for several days now, pushing the bloom and sick and dead sea turtles toward the coast.

From February: Red tide taking out larger fish, lingering in Lee

From April: High concentrations of red tide algae continue to kill fish in Lee, Collier

Onshore winds are expected to continue through Friday, according to the National Weather Service.

When waves crash on the beach they release the toxin into the air.

Kraus' voice was raspy Tuesday after spending several days at the beach and being exposed to the outbreak.

Most of the sick or dead sea turtles are trapped at the surface or stranded on a beach. Sick turtles are often unable to dive beneath the surface or evade predators like sharks.

"They float at the surface and the waves bring them in, but we only get a certain percentage of what’s dead out there," Kraus said. "We get what floats to the beach or if someone just happens to see one. Everything else decomposes or sinks after a while, so we get a small percentage and we know the numbers are actually higher."

Heather Barron is the head of the Center for the Rehabilitation of Wildlife, or CROW, veterinarian hospital on Sanibel.

Related: Sanibel scientist leading the local fight against red tide

Related: Red tide bloom killing fish, sea turtles in Fort Myers area

She said the red tide outbreak has collided with the height of sea turtle reproduction, something that doesn't often happen.

"This is way, way high," Barron said of the turtle numbers. "Normally red tide season is over in April. But now sea turtle nesting is at its peak and you have adults in nearshore waters. And because of that they’re being effected."

Red tide blooms are typically broken up by cold weather systems that come from the mainland during the winter months, which means this bloom could be here well into 2019.

Barron said this mortality event may leave a long-lasting imprint on Southwest Florida's sea turtles.

"This is so devastating to the population of sea turtles that was really starting to come back, and I fear this event will have an impact for years to come," she said.

Mote Marine Laboratory & Aquarium in Sarasota has seen about twice as many sea turtles as they get in an average year.

"We’re actually going out right now to pick up number 112 for the year," said spokeswoman Allison Delashmit. "We normally have about 100 turtles that we pick up in bring back for necropsy each year."

Connect with this reporter: Chad Gillis on Twitter.

How you can help

Call (978) 728-3663 to report a dead or injured sea turtle to the Sanibel-Captiva Conservation Foundation.