Scientists may have discovered what causes hundreds of fish off the coast of the Florida Keys to spin in circles until they die.
Reports of the bizarre behavior first surfaced in October 2023, leading to nearly 500 reports of dead fish washing up on May 8.
Researchers from Florida Gulf Coast University recently analyzed more than 300 samples of fish tissue and tested more than 250 chemicals in the area to determine what could be causing this deadly fish to spin.
The team has now identified toxic algae on the seabed in samples, suggesting the emergence of a bacterium linked to neurological deficits including hyperactivity and muscle twitching on the seafloor.
Researchers believe toxic algae growing on the seabed could cause hundreds of fish to develop neurological problems
The Florida Fish and Wildlife Conservation Commission (FWC) and researchers last month found six dead smalltooth sawfish washed up on the shores of the Florida Keys, which are on the brink of extinction.
The sight, a month of hundreds of reports, led to them launching an investigation.
The team sent the tissue samples to the University of South Alabama for toxin analyses, but reports indicated there was no evidence of low oxygen levels, low salinity, pH, strange water temperature or red tide – a type of harmful algae bloom.
Although more studies need to be conducted to officially determine the cause, the tests revealed natural toxins in both the seawater and fish tissues, and elevated levels of the HAB, Gambierdiscus algae.
Gambierdiscus toxicus, loosely attached to algae on coral reefs and then ingested by marine animals.
“The hypothesis that I’m working on right now is basically that the combination of these different benthic algal toxins come together to create the phenomenon that we’re seeing,” Alison Robertson, a senior marine scientist at the Dauphin Island Sea Lab, told me. NBC News.
Benthic algae live on the seabed off the coast, about 20 to 40 meters below the surface, and can release toxins during algae blooms – when the algae population in the water increases rapidly.
Scientists still don’t know what caused the population to grow, but are now in a race against time to protect the smalltooth sawfish and other species from further exposure.
There have been more than 500 reports of spinning fish off the coast of Key West. The smalltooth sawfish is most at risk as it is critically endangered, and the phenomenon has already claimed 47 lives
Tissue samples were sent to the University of South Alabama for toxin analyses, but reports indicated there was no evidence of low oxygen levels, low salinity, pH, strange water temperature or red tide.
There are also reports of smalltooth sawfish beaching themselves, adding to the increasingly worrying behavior of other fish that have been spotted spinning off the coast of the Florida Keys.
The cause continues to baffle scientists, who said that when they removed the spinning fish from seawater and placed them in a freshwater tank, some recovered in a span of just 25 minutes.
Michael Parsons, a professor of marine science at Florida Gulf Coast University and an algae expert, found that Gambierdiscus levels 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 mammal’s bloodstream through the food they eat, causing irregular swimming and death.
The algae has affected several fish species, 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 this number is believed to be much higher.
Researchers rescued a distressed smalltooth sawfish swimming in circles in Cudjoe Bay on April 5 and transported it to a temporary holding tank at the Mote Marine Laboratory in Sarasota, Florida.
The FWC and Mote hoped that by rehabilitating the small tooth they could better understand what caused the event, but as the animal continued to deteriorate, they decided to humanely euthanize the fish on May 2.
The smalltooth sawfish is a critically endangered species, probably due to habitat loss. The species once lived as far away as the coast of central West Africa to North Carolina
The FWC took blood and tissue samples from the rescued sawfish to determine if there were toxins in the system
“It has always been our cautious hope to use the best available science for sawfish rehabilitation and release,” says Dr. Michael P. Crosby, president and CEO of Mote Marine Laboratory & Aquarium.
“Although heartbreaking, this outcome was not surprising,” he said, adding: “We have worked restlessly around the clock to provide the most advanced treatment available.
“Unfortunately, even with our best efforts, the animal was ultimately too compromised to recover.”
The FWC performs a necropsy – animal autopsy – on the small tooth and sends samples to various laboratories for further analysis.
“I honestly don’t think anything can reasonably be ruled out at this point,” Crosby told NBC.
On May 6, more than 60 species were reported showing symptoms, including silver barbel, snook, bonefish, southern stingray, Atlantic sharpnose shark and swordfish, among others. Bonefish & Tarpon Trusta 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.