Florida Keys fish kill has scientists, fisherman concerned, probing for causes

Smalltooth sawfish, the shark-looking ray with a serrated rostrum, once ranged from Texas to North Carolina. But, these days, the only place you’ll likely find one is Florida, and even here, count yourself lucky if see one in the wild.

Now, a mystery has unfolded that is setting off alarm bells among fishermen and biologists alike about the future of the vulnerable animals, placed on the Endangered Species List in 2003 due to being killed in commercial fishing nets: 15 smalltooth sawfish have died in the Lower Florida Keys since Jan. 30.

“Currently, the cause is unknown,” said Kelly Richmond, a spokeswoman with the Florida Fish and Wildlife Conservation Commission’s Fish and Wildlife Research Institute. ”FWC continues to coordinate with partners to collect and analyze samples.”

The sawfish deaths are coinciding with a larger fish kill first noticed in November in the waters off Big Pine Key through Key West that’s so far impacted more than 20 species, from silver mullet to tarpon, snook, mangrove snappers and even lemon sharks.

Scientists collect samples from a mullet in the Florida Keys, where a fish kill has been happening since November 2023.
Scientists collect samples from a mullet in the Florida Keys, where a fish kill has been happening since November 2023.

The two phenomena may be connected, but so far, scientists are at a loss to explain what is going on.

“The stressor is invisible, the water is clear and pretty, habitat looks great, everything environmentally passes the eye test,” said Ross Boucek, a biologist with the Bonefish and Tarpon Trust, a South Florida fisheries conservation nonprofit.

On Nov. 7, an angler caught a snapper off the Lower Keys. When he released it, it spun to the bottom, an indicator a fish is sick, Boucek said.

Reports of sick, dying fish

Since then, the Bonefish and Tarpon Trust, as well as the Lower Keys Guides Association — a nonprofit for flats fishermen — has received more than 65 more reports of sick and dying fish in the region — many exhibiting the same spinning-type behavior. The FWC’s fish kill hotline has received more reports as well.

“I personally have seen symptomatic fish on more than a dozen different days and nights, and their behavior is definitely not normal,” Boucek said.

While scientists haven’t figured out what’s going on, they have ruled things out.

“These include red tide, or any other harmful algae that floats around in the water. It doesn’t seem to be a fish health problem, like virus or a parasite,” Boucek said. “Preliminary human contaminant (i.e. synthetic chemicals including pharmaceuticals) testing has come back negative, though additional testing will continue.”

Could it be connected to the unusually hot water in the shallow near-shore waters in the Keys last summer?

“Too early to tell,” Boucek said.”

Working with universities, state environmental agency

Since December, the Bonefish and Tarpon Trust has partnered with biologists from Florida International University, the University of South Alabama, the Florida Department of Environmental Protection and Florida Gulf Coast University to broaden its investigation.

“We’re keeping open minds and following the path the data are leading us, but no definitive answers yet,” Michael Parsons, a professor of marine science and director of the Vester Field Station at Florida Gulf Coast University in Fort Myers, told the Herald.

A lead that scientists are following is the presence of elevated levels of a harmful algae known as gambierdiscus found in parts of the ocean and Gulf of Mexico, where fish have been discovered dead or exhibiting the same type of spinning behavior first reported by the angler in November.

“Correlation is certainly not causation, but this is a lead,” Boucek said.

Biologists at Florida Gulf Coast University and the University of South Alabama are testing samples of gambierdiscus collected in the Keys, Parsons said.

The finding is gaining attention in the scientific and fishing communities because gambierdiscus is contained in a toxin that causes a type of food-borne illness called ciguatera.

Vials of water and fish tissue samples are placed in a container. The samples were taken from fish and the waters off the Lower Florida Keys, where scientists have been investigating a fish kill since November 2023.
Vials of water and fish tissue samples are placed in a container. The samples were taken from fish and the waters off the Lower Florida Keys, where scientists have been investigating a fish kill since November 2023.

Ciguatera is found in algae that grows on coral reefs in tropical and subtropical waters like those surrounding the Keys. Fish that feed off the reef ingest the toxin in their flesh, and it moves up the food chain as those fish are eaten by bigger fish.

That’s why it’s a generally a bad idea to eat barracuda, although restaurant favorites like mahi mahi, hogfish and grouper can also carry ciguatera, scientists say.

People poisoned from eating fish containing the toxin experience unpleasant gastrointestinal, neurological and even cardiac symptoms that typically resolve within a few days, but could last weeks, according to Johns Hopkins School of Medicine.

It’s odorless and colorless and can’t be eliminated by cooking the fish.

Painstaking investigation

Alison Robertson, from the University of South Alabama is leading researchers examining the samples. The task is daunting, Parsons said, because they must look for one molecule of ciguatoxin among millions of other compounds.

While fish can accumulate enough ciguatoxins to ultimately die, many fish in areas where ciguatera is present will have low levels in them — not enough to kill them, but enough to make people eating them sick, Parsons said.

Thus, investigating whether gambierdiscus is linked to ciguatera will take more research before it can be conclusively proven or disproven.

“We haven’t seen that in Monroe or Miamai/Dade counties, so we could be dealing with something different than ciguatera/ciguatoxins,” Parsons said.

To report any unhealthy, injured or dead sawfish, contact the FWC Sawfish Hotline at 844-472-9374 or via email at Sawfish@myfwc.com with the date, time and location of the encounter, estimated length, water depth and any other relevant details. See also NOAA’s smalltooth sawfish safe handling and release procedures.

If you see abnormal fish behavior, fish disease, fish kills to FWC’s Fish Kill Hotline either through the web form MyFWC.com/ReportFishKill or by phone 800-636-0511.

This story has been updated to report the number of dead smalltooth sawfish confirmed by the Florida Fish and Wildlife Conservation Commission since Jan. 30 is 15. The agency had previously said 17 have died.