The death toll for endangered sawfish in a mysterious fish kill hitting the Lower Keys now stands at 17 as scientists struggle to determine what’s harming a wide variety of fish in a way they’ve never before encountered.
As of this week, state officials have received nearly 100 reports. They confirmed Friday that the new death toll for rare smalltooth sawfish, which are found almost exclusively in South Florida.
“It's kind of a Sherlock Holmes mystery here,” said Mike Parsons, who studies toxic algae blooms at Florida Gulf Coast University and is part of a team assisting the state investigation. “By process of elimination we're trying to get down to the root cause or causes. The fact that so many different fishes are being affected is concerning.”
READ MORE: Endangered sawfish have been found dead in Lower Keys. Other fish also dying
Sick or dying fish were first spotted in the Lower Keys in early November.
Most sightings occurred between Bow Channel near Cudjoe Key and south to Big Pine, according to Ross Boucek, a scientist with Bonefish Tarpon Trust.
Sick fish initially appeared at night spinning or flopping upside down in a whirling pattern usually linked to freshwater fish infected with parasites. As daytime sightings popped up, guides started collecting fish and working with BTT to sample water.
By January, testing ruled out the usual culprits in fish kills: red tide that typically appears in the Gulf of Mexico and can spread south, extreme hot or cold temperatures and low oxygen.
Scientists also looked “for parasites, looking at any obvious disease vectors or anything like that,” Parson said. “Again, nothing obvious.” Parsons also looked for reports of chemical or sewage spills, but found none. Those spills would have also left a trail of damaged seagrass and other marine plants.
So Parsons said the team started focusing on elevated levels of a tiny, single cell algae found in ciguatera. Ciguatera is normally found in reef fish because the algae grows naturally on reefs. It can also be found in seagrass and seaweed. Fish can safely metabolize it, but people who eat the fish can become sick. The state has been monitoring cigua toxins in the Keys for about a decade and that monitoring data showed an increase this winter.
What’s not clear is why a toxin that exists naturally in the Keys might suddenly become toxic to fish.
“A toxin isn't toxic to everything, so is this a fish specific toxin?” Parsons said.
Identifying the tiny toxin can also be tricky since it can affect fish differently and change once fish begin digesting it, Parsons said.
“That means not only do we have to know what signal we're looking for, but it's a moving target,” he said. “It's also very potent and potent at really, really small concentrations. So that means the signal we're trying to look for is a really small signal. And so that makes it even harder.”
It’s possible the toxin is entering the fish through their gills, he said, which would bypass any protective process in the fish’s gut.
“The fact that you have mojarras and pinfishes versus a sawfish, they're eating different things, but they're all living in the same environment,” he said.
For now, Parsons said they’re focusing on the ciguatera toxin but continuing to look for other causes as they collect more samples. But, he said, it’s also possible that something completely different is causing fish to get sick and die.
“There's other chemicals and pollutants in the water that we aren't really monitoring or paying attention to. There's not enough time and resources,” he said. “Unfortunately, we tend to wait until something looks like it's a problem and then we throw resources at that, and then we try to understand it and then see what we can do about it.”
The fish kill comes on the heels of a devastating ocean heat wave over the summer that spread across Keys reefs and left many coral bleached. This month, the National Oceanic and Atmospheric Administration said nearly 80 percentof lab-bred staghorn coral planted on the reef to help revive it had bleached. Only two of the five reefs surveyed had any living staghorn coral remaining.
Having a fish kill so soon after the heat wave has some residents worried about more bad news and images of dead sawfish driving away tourists and customers. Fishing guides and tour operators especially worry about sick fish.
“If it’s something like ciguatera, that’s an issue if it’s widespread and in fish we’re eating,” said Joyce Millelli, who discovered a sick sawfish near Geiger Key while leading a paddle board tour in January that later died. “It can affect humans so we need to know.”
