Scientists may have discovered what has caused hundreds of fish off the coast of the Florida Keys to spin in circles to their deaths.
Reports of this strange behavior first emerged in October 2023, leading to nearly 500 reports of dead fish washing ashore as of May 8.
Researchers at Florida Gulf Coast University recently analyzed more than 300 fish tissue samples and tested more than 250 chemicals in the area to determine what could be causing this deadly fish turn.
The team has now identified toxic seafloor algae in samples, suggesting that a bacteria emerged on the seafloor that is linked to neurological deficits including hyperactivity and spasms.
Researchers believe toxic algae growing on the sea floor could be causing hundreds of fish to have neurological problems.
The Florida Fish and Wildlife Conservation Commission (FWC) and researchers found six dead smalltooth sawfish stranded on the shores of the Florida Keys last month, which are on the brink of extinction.
What we saw, a month with hundreds of complaints, led to an investigation being opened.
The team sent the tissue samples to the University of South Alabama for toxin analysis, but reports showed there was no evidence of low oxygen levels, low salinity, pH, unusual water temperature or red tide – a type of harmful algal bloom.
Although more studies need to be done to officially determine the root cause, tests revealed naturally occurring toxins in both seawater and fish tissues, and elevated levels of HAB, the algae Gambierdiscus.
Gambierdiscus toxicus, loosely attached to coral reef algae and then ingested by marine creatures.
“The hypothesis I’m working on right now is really that the combination of these various benthic algal toxins are coming together to create the phenomenon we’re seeing,” said Alison Robertson, a marine scientist at the Dauphin Island Sea Lab. NBC News.
Benthic algae live on the seafloor off the coast, between 65 and 131 feet below the surface, and can release toxins during algal blooms, when the population of algae in the water increases rapidly.
Scientists still don’t know what caused the population growth, but they are now in a race against time to protect the smalltooth sawfish and other species from further exposure.
There have been over 500 reports of fish spinning off the coast of Key West. The smalltooth sawfish is at the greatest risk because it is critically endangered and the phenomenon has already claimed 47 lives.
Tissue samples were sent to the University of South Alabama for toxin analysis, but reports showed there was no evidence of low oxygen levels, low salinity, pH, unusual water temperature or red tide.
There have also been reports of smalltooth sawfish stranding, adding to the increasingly concerning behavior of other fish that have been seen spinning off the coast of the Florida Keys.
The cause has continued to puzzle scientists who said that when they took the spinner fish out of seawater and placed them in a freshwater tank, some recovered within just 25 minutes.
Michael Parsons, a marine science professor at Florida Gulf Coast University and an algae expert, found that levels of Gambierdiscus were four times higher than he had ever seen or recorded before.
Last month, the FWC reported that Florida had seen an overgrowth of toxic algae that can enter the bloodstream of mammals through the food they eat, causing erratic swimming and death.
The algae has affected several species of fish, but marine biologists are most concerned about the smalltooth sawfish, which has been classified as critically endangered since 2003.
The FWC reported that 47 sawfish have died, but the number is believed to be much higher.
Researchers rescued a struggling smalltooth sawfish swimming in circles in Cudjoe Bay on April 5 and brought it to a temporary storage tank at the Mote Marine Laboratory in Sarasota, Florida.
The FWC and Mote hoped that by rehabilitating the small tooth they would better understand what caused the event, but when the animal continued to deteriorate, they decided to humanely euthanize the fish on May 2.
The smalltooth sawfish is a critically endangered species, believed to be due to habitat loss. The species once lived as far as the coast of west-central Africa to North Carolina.
The FWC took blood and tissue samples from the rescued sawfish to determine if it had toxins in its system.
“We have always been cautiously hopeful that we could use the best science available for the rehabilitation and release of sawfish,” said Dr. Michael P. Crosby, president and CEO of Mote Marine Laboratory & Aquarium.
“While heartbreaking, this result was not surprising,” he said, adding, “We work tirelessly around the clock to provide the most advanced treatment available.”
“Sadly, even with our best efforts, the animal was ultimately too compromised to recover.”
The FWC is performing a necropsy (animal autopsy) on the small tooth and is sending samples to several laboratories for further analysis.
“Honestly, I don’t think anything can reasonably be ruled out at this point,” Crosby told NBC.
As of May 6, more than 60 species were reported to have symptoms, including mullet, snook, bonefish, southern stingray, Atlantic sharpnose shark and swordfish, among others, according to Bonefish and Tarpon Confidencea marine conservation agency.
The organizations are asking the public for help identifying other deaths or abnormal behavior by calling the sawfish hotline: 844-4-SAWFISH.
