The smalltooth sawfish, one of Florida’s most iconic yet endangered species, is facing an alarming and mysterious threat.
Once widespread, the range of this rare fish has dramatically shrunk over the years.
However, the brackish mangrove waters of Lee and Collier counties remain one of the last strongholds for these creatures, serving as crucial breeding grounds.
Yet, disturbing videos from late 2023 tell a troubling story. Footage from Cudjoe Key shows a massive sawfish in visible distress, part of a broader pattern of fish spinning erratically and dying. Scientists and conservationists are still searching for definitive answers to what’s causing these events, which seem to be resurfacing once again.
After a six-month lull, the issue has re-emerged. In just the past four months, at least six dead sawfish have been confirmed in the Florida Keys, accompanied by dozens of reports of spinning fish. This resurgence has prompted scientists to revisit the phenomenon and investigate the underlying causes.
Florida Gulf Coast University’s Dr. Mike Parsons was among the first researchers called to investigate when local fishing guides noticed the erratic behavior in October 2023.
“The event started last October, that’s when local fishing guides started getting concerned about erratic fish behavior, spinning fish,” Parsons said. “They asked the state and Bonefish Tarpon Trust to get involved.”
While fish kills are not uncommon in Florida — often attributed to red tide or low oxygen levels — Parsons and his team have ruled out these typical culprits.
“Neither of those appear to be related at all to these spinning fish,” he said.
After months of sampling and analysis, researchers suspect a specific type of plankton may be responsible.
“The evidence still points to the benthic dinoflagellates producing neurotoxins that are causing the behavioral effects we are observing,” Parsons said. “We saw the first evidence of this about mid-October last year.”
Benthic dinoflagellates, a type of bottom-dwelling plankton, can release neurotoxins into the water. Dr. Ross Boucek from the Bonefish Tarpon Trust suggests that unseasonably warm temperatures may be triggering an overgrowth of these toxic plankton.
“The event intensified about mid-March last year, and then as waters warmed, the phenomenon went away during the summertime,” Boucek said. “The temperatures it was really peaking at are the preferences of benthic dinoflagellates, particularly the Gambierdiscus species.”
Though the findings are not yet conclusive, the recent uptick in spinning fish and sawfish deaths has researchers deeply concerned. The possibility that this could become a seasonal trend poses a severe threat to an already endangered species.
“I went home to visit my parents in Naples, Florida,” Boucek said. “In one afternoon, I got seven different calls of spinning or dead sawfish. Even if it’s just four or five a year, what does that mean for this species? How do we account for that mortality? How do we save more sawfish lives to keep the population sustainable?”
Despite ongoing research, scientists still don’t fully understand what’s causing this strange behavior and the increasing number of sawfish deaths.
In the coming weeks, Boucek will continue investigating, taking water samples in the Keys to determine if neurotoxins are indeed the culprit.