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Environment

'There Was Just Turtle After Turtle After Turtle': Could Sea Turtles Be Surging In Biscayne Bay?

Sea turtle
University of Central Florida Turtle Lab
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Most of what we know about sea turtles comes from nests on beach. But nearly all their life occurs at sea.

On a flat calm day earlier this month, Dirk Jacobs was speeding south just outside Biscayne Bay in his 22-foot bay boat when he spotted something he’d not seen in a half century of fishing: hundreds of sea turtles, their heads bursting from the placid waters like popcorn.

“You know, we see turtles all the time. So boom, there was a turtle,” he said.

But then he saw another. And another. And another.

“We're probably doing 25, 30 miles an hour, so it was literally just one every couple of seconds,” Jacobs said. “We're actually swerving the boat to get away from their swirls.”

Jacobs was trying to keep count of the bobbing heads when his son told him to stop and look below the surface.

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“It was crystal clear and there was just turtle after turtle after turtle after turtle, generally in the edges of the grass beds as they met the sand. And it went on, for however far it is from Sands Cut down to about Pacific [Reef] Light,” he said. “It was just nonstop. You're looking down on the water and it was one turtle after another.”

Jacobs reported what he saw to the University of Miami’s aquaculture director at the Rosenstiel School, who forwarded the email to biologists. In June, dozens of young turtles were also spotted on the flats near Sands Key.

The observation piqued their interest because so little is known about what turtles do at sea, making Jacobs among the lucky few to observe what scientists call the turtles’ lost years.

“If he truly saw hundreds of turtles, that would be something spectacular,” said Chris Sasso, a fisheries biologist with the National Oceanic and Atmospheric Administration on Virginia Key. “It is possible. There’s places we’ve worked where we’ve seen 60-plus turtles in 20 minutes.”

It’s also remarkable that it occurred near Biscayne Bay. With its beaches and seagrass meadows and easy access to reefs, waters around the bay are ideal turtle territory. Yet fewer have been documented than in other places up the coast, from Palm Beach County to Titusville.

Part of that has to do with research and limited resources, biologists say. It’s easier to investigate stationary nests on a beach. And until recently, technology — including micro tags and solar-powered satellite trackers needed to track tiny baby turtles or big turtles over long distances — weren’t available, said University of Central Florida turtle biologist Kate Mansfield.

taggedloggerhead_jimabernathy.jpg
Credit Jim Abernethy / University of Central Florida Turtle Lab
A baby loggerhead sea turtle with a tracker attached to its back.

“It's a bit like bobbing for apples blindfolded in a way, because you may not know exactly where to look,” she said.

But that’s changing, especially in Biscayne Bay, which sits along an important migratory path. In 2018, U.S. Geological Survey biologist Kristen Hart launched a tracking study to look at where the Biscayne turtles go. And Sasso is now heading up a NOAA study monitoring turtle swimming patterns and boat traffic to get a better understanding of their behavior and risks in the bay.

Ultimately, the goal is to help revive the bay’s turtle population and understand how it fits into the global turtle puzzle.

“If 2020 could be good for something,” Hart said, “it’d be nice if it was good for turtles.”

UNDERSTANDING THE LOST YEARS

It’s a lofty goal. Turtles can take 20 to 30 years to mature, so lost years at sea can last decades as the turtles move from nesting beaches to foraging grounds, sometimes across oceans. And if something happens to a generation — disease or a catastrophe like an oil spill — it may take years to recover.

That’s a long time to ensure conservation policies and money is in place to protect turtles, from increasing threats like worsening plastic pollution and over-developed coasts. It’s also why understanding the lost years is so critical.

Scientists had long suspected turtles lucky enough to make it offshore after they hatched — on average, only one in a thousand do — lived in mats of sargassum, floating passively with the algae or carried by currents.

“Everyone just assumed that the turtles would passively drift in a big circle around the Atlantic and that they would just ride the currents,” Mansfield said. 

Specifically, they thought turtles would ride the circular currents that make up the massive North Atlantic Subtropical Gyre. That would take the turtles over to the Azores Islands, where they might get picked up by the Canary Current and carried to the Canary Islands, over to Cape Verde off the West African coast and then back to the U.S. and Bahamas by way of the Equatorial Current, Mansfield said.

That theory was bolstered by DNA testing that showed turtles off the Azores and Cape Verde were genetically related to Florida turtles. 

That’s part of what makes studying them offshore so difficult: the mats can easily break up or shift with currents.

loggerhead_tagged_jim_abernathy.jpg
Credit Jim Abernethy / University of Central Florida Turtle Lab
A juvenile loggerhead is outfitted with a tracker by the University of Central Florida Turtle Lab to trace its movement.

“It's not like if you're studying, say, a bird that lives part of its life in a forest” Masfield said. “You can always go to that forest because the trees are going to be rooted there.”

TRACKING THE TURTLES

But work done by Mansfield and other labs is changing that by attaching tiny trackers to the baby turtles. This year, one of her students received a NASA grant to also model the sargassum movement.

Instead of floating along the currents, the trackers showed a large number of both green turtles and loggerheads swam into the gyre and into the Sargasso Sea. (The team also released drifters to confirm the turtles and the currents were parting ways.)

“So it's really cool that the Sargasso Sea is emerging as a very important nursery habitat for a lot of sea turtles that emerge off of our beaches up and down the Florida coast,” she said.

What turtles do when they mature, between 25 and 35 years old, remains another piece of the puzzle. Females reliably return to beaches where they hatched to lay eggs, but males never return to land.

“Think about it, because humans go through puberty at age eleven, twelve, thirteen, fourteen. These turtles have twice as long,” she said. “So if something happens to their population, if they are heavily fished out, say, 30 years ago, it may take at least a generation to three generations before their population can rebuild.”

That’s where Hart and Sasso come in. If they can understand how turtles inhabit coastal waters, and what threats they face in the water — not just on beaches — they can improve management practices.

Hart, an expert in tracking who also tags pythons, has tagged 50 turtles in Biscayne Bay since 2018, in addition to turtles in the the Dry Tortugas and Everglades National Park. Her team tracked a Biscayne turtle swimming to Jupiter where it nested before returning to the bay. Another turtle was found in the bay that had been tagged nesting in Sanibel.

tagged_loggerheads_mansfield.jpg
Credit Kate Mansfield / University of Central Florida Turtle Lab
Baby sea turtles outfitted with trackers and ready to be released.

“We're piecing this together year by year,” she said. “Some days we get six turtles. Some days we get three. I just feel like every turtle counts and we're starting to understand what the composition is.”

It’s not just their movements she’s watching, but when they move.

“Like January movements. Like what are they doing? Why are they leaving in January? You know?” she said. “If you're a male or if you were subadult, if you're becoming a mature individual, when are you making what I call risky movements or where are you going to mate?”

DNA testing has shown that turtles swimming and feeding around Florida aren’t just coming from adjacent beaches, but all over. One turtle swam from the Dry Tortugas to the northern coast of Nicaragua. Turtles sharing foraging grounds have also been found to have hatched from many different beaches.

She also found turtles that appear to be local, who may travel short distances to nest, but don’t venture beyond Florida waters.

“It's starting to be kind of a trend,” she said. “Biscayne is uniquely situated along the migratory corridor for a lot of animals. So that's one of my questions generally, like, am I going to have a lot of resident animals or are they just gonna be booking through going north or south?”

If they do stay put, she says it’s also important to understand how the locals might interact with migrating populations, possibly like the ones Jacobs observed.

“We think some of the adult males might actually be living right on the reef tract, which is a pretty ideal spot for a male that wants to breed with females coming through,” she said.

Whether they stay in the bay or migrate along the busy waters, understanding the threats they face is important to protecting and managing the population.

For that, Sasso is working with the University of Miami Rosenstiel School to track turtle movements and compare it to boat traffic.

“One of the larger concerns for sea turtles, much like manatees, are boat strikes because they do spend time loafing at the surface,” he said. “You could actually pick out particular weekends, like [if] the Fourth of July was in the middle of the week. You could see that vessel traffic and you could determine the difference between weekend vessel traffic vs. weekday. So there were some interesting patterns with that.”

What he finds could help better manage the bay, which has suffered not just from increasing boat traffic but pollution from its urban neighbor. More than 25 square miles of seagrass —where green turtles would graze or forage for sponges and loggerheads might hunt for shrimp and crabs — have been killed. Last year, NOAA reported that the gin clear waters of the bay were undergoing a regime shift to a murkier bay filled with macro algae.

RETURN TO FORMER GLORY?

As the number of turtles increase — and at least for green turtles, the population has been booming — understanding movements and life cycle habits could help continued success, Mansfield said.

The 30-mile stretch of beach her lab monitors between Patrick Air Force Base and the Sebastien Inlet represents more than a third of all green turtle nesting in Florida. In the last decade, she said nesting numbers have increased exponentially, just four decades after harvesting turtle meat became illegal.

“We're slowly starting to see these turtles come back to maybe a hint of what their former glory might be,” she said.

Dirk Jacobs with a tuna
Credit Courtesy Dirk Jacobs
Angler Dirk Jacobs, pictured here with a tuna, said he spotted hundreds of turtles last month as he motored along the outer reef south of Sands Key.

Weeks after he spotted the thundering herd off the reef, Jacobs still marveled at the sight.

“Seeing those turtles was super exciting, even for my son and he doesn't get excited about anything. He was thrilled by it,” he said. “I've spoken to ten people since about it. No one's ever seen that many turtles.”

There is one thing he says he’ll do differently: have his camera ready.

“Now my GoPro, since that day, is a permanent fixture on the boat,” he said. “I want to make sure I get videotape of all these things.”