Reports of distressed or dying rare sawfish in the Lower Keys have climbed to 39 as scientists race to determine what’s killing one of the planet’s most endangered species amid an outbreak of unusual fish behavior in Florida waters.
As of Tuesday, 15 smalltooth sawfish had been retrieved for testing, according to Florida Fish and Wildlife Conservation Commission officials, who are investigating the deaths.
“Are the two related? We can’t definitely say that, but we’re pursuing this with every means we have,” said Tom Matthews, a biologist who manages the Florida Wildlife Research Institute’s Marathon lab.
READ MORE: Mystery in the Keys: Sawfish deaths rise to 17. Scientists search for clues
Sick fish were first spotted in early November. Many exhibited a whirling behavior and were mostly observed at night, according to the Bonefish Tarpon Trust, which began collecting reports from the Lower Keys Guides Association and helped organize a team to investigate. Soon that spinning behavior turned up during the day and included more than two dozen species of fish, including rays, tarpon, snook, mutton and yellowfin snapper, mullet, pinfish and ballyhoo.
The first dead sawfish was found more than two months later, on Jan. 30. More reports of distressed or dead sawfish followed, escalating concern among scientists that whatever was causing other fish to fall sick was now killing a species so rare it can now only be reliably found at the southern tip of Florida.
“There are five species of sawfish in the world. That's it. And they're all listed as endangered or critically endangered,” said Dean Grubbs, a Florida State University fish ecologist and a member of the National Oceanic and Atmospheric Administration’s sawfish recovery team. “So an occurrence like this, where all of a sudden quite a few large animals are dying inexplicably, is of great concern.”
In 2003, smalltooth sawfish became the first native fish added to the endangered species list after being nearly wiped out. Their large, toothy rostrum - that can be nearly a third of their body length - easily snares in nets. That bycatch accounted for most of their deaths. Estuaries where female sawfish gave birth to pups also got hammered by pollution and over-development. Because they grow slowly and don’t start reproducing until they reach 8 to 10 years old, numbers plunged.
By the 1950s, sawfish that once inhabited waters from the Carolinas to Texas could only be found reproducing in two areas near Charlotte Harbor and the Everglades Ten Thousands Islands.
Netting bans and protecting nurseries with the creation of Everglades National Park and other marine preserves have helped their numbers rebound, Grubbs said.
But little remains known about adult sawfish, leaving scientists puzzled over why they might be more vulnerable to whatever is making fish in the Lower Keys sick.
“Even though they lay on the bottom, they're highly mobile. They can move fast,” Grubbs said. “So why they wouldn't move out of an area that potentially has something toxic in it, I don't know.”
Since the majority of dead sawfish and other species falling sick have been found between Bahia Honda and Key West. Grubbs believes whatever is occuring for now is contained to that area. Last week when his research team was working in the Keys, they captured and tagged eleven healthy sawfish about 14 miles further east near Marathon.
“The largest one was 14 feet long and they all seemed perfectly healthy,” he said. “So, of course, the hope is that whatever's causing this doesn't spread further up the Keys.”
For now, the leading culprit driving the deaths is a single-celled algae, or dinoflagellate, commonly found in ciguatera. The naturally occurring toxin was detected at elevated levels in water samples in the Lower keys. The toxin can accumulate in large fish and frequently gets blamed when people fall sick after eating reef fish. But it typically does not harm fish.
That suggests something different is happening now, said Mike Parsons, a Florida Gulf Coast University algae expert who is part of the team investigating the cause. The toxin could be affecting only some fish. Or rather than ingesting it, so that the stomach and liver process the toxin, they’re absorbing it through their gills, he said.
“A toxin isn't toxic to everything. So is this a fish specific toxin?” he said. “We realize there's other potential answers out there and we just need to see if there’s enough information to continue down this path, or are we barking up the wrong tree and we're going to have to switch over. But right now we're looking at this tree.”
The dinoflagellate can appear after a disturbance, like a hurricane. The summer ocean heat wave, which caused coral to bleach across the Keys and pushed near shore water temperatures into the 100s, could be a trigger, Matthews said. Measuring toxin levels in water where the heat wave was higest and comparing that to area where water was cooler could help find that answer.
In the meantime, the spread of diseased fish has fishing guides worried and frustrated the state officials took too long to begin investigating,
“All the guides down there are super concerned because it’s affecting baitfish and crustaceans. That’s a major concern for their fishery,” which includes a trio of sportfish that inhabit flats and draw high-paying anglers to the upcoming tarpon season, said Capt. Benny Blanco. “Already they’re concerned that permit are not in town.”
Starting an investigation in January, two months after guides began spotting the unusual spinning, wasted time, he said.
“When the guides are screaming like that, FWC should roll out the band wagon,” he said. “And they just took too long”
This story was produced in partnership with the Florida Climate Reporting Network, a multi-newsroom initiative founded by the Miami Herald, the South Florida Sun Sentinel, The Palm Beach Post, the Orlando Sentinel, WLRN Public Media and the Tampa Bay Times.
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