Mysterious fish killer – Bonita Springs Florida Weekly

Researchers say 46 sawfish have died but they fear the illness killed many more.

It’s a mystery. Fish in the Florida Keys are dying horrible deaths, spinning and thrashing at the surfaces. The biggest concern is the endangered sawfish. Scientists are working around the clock to find what is decimating their numbers. They’re worried about how many have died, how quickly it’s happening, and how the fish perish. So far, they have no definitive answers.

The smalltooth sawfish are usually bottom dwellers. But the sick ones are seen at the water’s surface spinning, swimming in circles and upside down, thrashing and even beaching themselves in shallow waters, as many ill marine mammals will do. The dramatic throes of death may continue intermittently for hours or days before the end.

It’s not a quiet death.

The sawfish, once plentiful in the U.S., plied the coastal waters from Texas to North Carolina, but are now reduced to a small concentration in the Florida Keys, and a small population off the Bahamas. The spinning phenomenon has been seen in the Lower Keys, starting in late January.

Sawfish are endangered. Experts say only a few hundred breeding-aged adults remain in the wild.

The Carnage

So far, 46 carcasses have been documented. But there may be many more, according to Adam Brame, sawfish recovery coordinator for NOAA Fisheries. Sawfish sink to the bottom when they die, he explains, so it’s hard to know how many remain uncounted. Asked if he could provide an estimated number, Brame replied,

“A lot.”

NOAA, the National Oceanic and Atmospheric Administration, heads an emergency response effort to try to rescue and rehabilitate the sawfish. The team includes federal and state agencies as well as private aquariums and nonprofit groups.

Brame has been the recovery coordinator since 2015, charged with working on updating the NOAA Fisheries plan for the sawfish, to eventually recover from its endangered species status. Then the mysterious sawfish deaths started happening.

The strange, almost prehistoric-looking fish has been around for more than 50 million years. It can grow to 20 feet long and is characterized by a long-extended snout that looks like a saw blade lined with sharp teeth. Brame describes it, as “part shark at the tail, part ray in the middle and a hedge trimmer in front.”

Crews rescued a sick sawfish in the Florida Keys. MOTE MARINE / COURTESY PHOTO

The hedge trimmers are referred to scientifically as rostrums. “Although they swim like sharks, they are more closely related to stingrays because they have gill slits under their bodies rather than on the sides of their bodies.”

The sawfish easily entangle in fishing gear. Sawfish rostrums have also been popular trophy items, the FWC says.

Smalltooth sawfish were categorized as endangered nationally just over 21 years ago. Florida had already categorized them as endangered in 1992. The reason for dwindling numbers is overfishing and loss of habitat, largely due to coastal development.

Experts estimate the total number of breeding females to be 650, but Brame says he takes that number with a grain of salt. Brame says there are probably “a few hundred” breeding adults left.

Adam Brame sawfish recovery coordinator for NOAA Fisheries. ADAM BRAME / COURTESY PHOTO

The sawfish affected by this most recent illness are large juveniles and adults, 7–14 feet long. The lone sawfish rescued April 5 off Cudjoe Key underwent intensive rehabilitation at Mote Marine Laboratory in Sarasota. But the male, measuring 11 feet, 2 inches long died on Friday.

Is the current situation dire enough to lead to extinction?

“I think it is too soon to tell,” Brame says.

“I think that our response is indicative of our concern level. I think that sawfish have a small population to begin with. And when you’re talking about the removal of a lot of mature animals, or close to being mature animals, you really hinder the species’ ability to reproduce and keep the population viable. The longer it continues, the higher that concern level is. And I think that’s to some degree why we’ve put forward this effort in trying to rescue, to protect the viability of the species.”

PARSONS

In a statement on the NOAA website, Brame says,“Given the limited population size of smalltooth sawfish, the mortality of at least two dozen sawfish could have an impact on the recovery of this species.”

Now the death toll is approaching twice that amount.

The phenomenon

Sawfish are not the only species affected by this strange marine malady.

The whole spinning fish phenomenon started in late October 2023 with reports of the abnormal behavior seen in what has now added up to 52 species of fish, says the FWC. They include lemon, blacktip and nurse sharks, stingrays, snook, snapper, mullet, jacks, pinfish, stone crabs, goliath grouper, tarpon, and more.

The usual suspects have been ruled out. It’s not red tide, not bacteria, not problems with oxygen levels or salinity, not parasites, not pesticides or herbicides.

For the most likely suspect, you must get in the weeds, or in this case, seagrasses.

The research is leaning toward toxins produced by a tiny microalga called Gam- bierdiscus. At least in terms of what’s affecting “bony” fish, says Michael Parsons, a marine science professor and director of the Vester Field Station at the Water School of Florida Gulf Coast University. He’s talking about snapper, jack, snook, essentially any fish that has a skeleton made of bone. Parsons says this could also be what is affecting sawfish, but it’s too soon to say.

Michael Parsons of the FGCU Water School and a team are sampling water from the Keys. MICHAEL PARSONS / COURTESY PHOTO

Gambierdiscus, a single-celled organism no larger than a grain of sand. It usually lives on the bottom of seagrass blades and seaweeds. Parsons explains, “but it was present in the water column, and it was present at levels about ten times higher to 100 times higher than we typically see it. And so that led us to suspect that maybe Gambierdiscus was involved.” The usual number is 30 cells of Gambierdiscus per liter of water. However, researchers recorded up to 5,000 cells per liter in some cases.

Gambierdiscus produces neurotoxins. These toxins, when accumulated up the food chain, can cause ciguatera poisoning. Parsons says “my role in all this is I’ve been studying ciguatera for 15 years down in the Keys. And so I’m very familiar with Gambierdiscus and other benthic dinoflagellates (scientific name for bottom-dwelling microalgae).”

Researchers at Mote Marine Laboratory tend to a sick sawfish which later died. MOTE MARINE / COURTESY PHOTO

He says something eats the Gambierdiscus cells, usually a fish feeding on the seagrass and the seaweed.

“That toxin becomes internalized. Then a predator eats them, a bigger predator eats them, and the toxin accumulates as you move up through the food web.” Then people eat the fish and can get seafood poisoning, it’s neurotoxic. “So besides gastrointestinal distress, people may notice their fingertips going numb, their lips going numb.”

While ciguatera is usually transferred through diet, “the fact that we have over 50 species of these bony fishes exhibiting this erratic behavior suggests it’s not diet related, because they all don’t eat the same things and they’re not all the top predators.” Parsons says. “So that had us suspecting that it’s a waterborne exposure, so it must be toxins released into the water.”

Scientists examining a sawfish carcass to figure out what’s behind the mystery. FWC / COURTESY PHOTO

“Another interesting thing is, you can take a spinning fish and put it in ‘clean’ water, and many of them will recover,” Parsons says. “They’ll stop spinning and they’ll return to normal behavior.”

Research shows there may be other microalgae, along with Gambierdiscus, producing toxins that are causing the erratic behavior in fish.

However, Parsons says, “We haven’t looked at enough sawfish samples to know if it’s the same cause for them or the same suspected cause.” Since sawfish are endangered, it’s harder to get tissue samples “and then you have the lag when you finally get your hands on the tissue samples to do all the toxin analyses on them. Plus, there were hundreds of other fishes already in queue to do the toxin analyses.”

They are working with Alison Robertson, a marine scientist at the University of South Alabama and at Dauphin Island Sea Lab, for toxin analysis.

The Rescue

One sick sawfish was rescued in the Keys more than a month ago. It received treatments at Mote Marine Laboratory including tube feeding, oral vitamins and blood draws for analysis. Despite early reports that the sawfish was responding it died Friday, May 3.

Due to weather conditions, staff and logistics, no additional rescues have been attempted.

“I know the public wants us to be rescuing more,” Brame says. “And, you know, we’d certainly like to rescue more as well. But there’s so many factors that come into play in trying to manage a large animal that’s 11 to 14 feet in length and is sick. And they have this weapon on the front of their body, and then you’re trying to make sure that they can breathe, and they don’t dry out.”

For the April 5 rescue, the logistics happened to be right. They received the report, and a boat was in the vicinity. When the boat reached shore, the sick sawfish was hand-lifted in a sling and put directly into a large tank. The fish was out of water for about 10 minutes, says Brame.

“We have a couple of different tanks available at different locations in the Keys to help with this rescue effort.” “Again, it goes back to, if it’s too far of a distance to get the sawfish from the water to the tank, then it’s not really a good opportunity, right? We don’t want the sawfish to die in that short-range transport. So that’s why each one is case-specific.”

The sawfish was stabilized over several days and when it seemed ready to make the seven-hour trip, a truck the size of a semi-truck from Ripley’s Aquariums, carrying a giant tank, with all the associated life support systems, filters and generator took the sawfish to Mote Marine Laboratory. “It’s essentially a mobile aquarium,” Brame says. “It took a great team.” Other than Mote and Ripley, Havenworth Coastal Conservation and Dynasty Marine Associates helped in the rescue.

Other Factors

The reports of spinning sawfish have generally been isolated to the lower Florida Keys, but there have been reports of a sawfish acting erratically in Boynton Inlet in Palm Beach County, as well as in Everglades National Park near Flamingo.

“Whether they’re completely related to this event or not is unknown.”

What about climate change as a factor? The water around the Keys became super-heated last summer. Meteorologists reported a buoy in Manatee Bay, northwest of Key Largo, measured temperatures of 100 and 101 on two consecutive days in July.

“It may have just changed some of the conditions that maybe allowed Gambierdiscus and these other benthic dinoflagellates to thrive more,” Parsons says.

“Maybe they had predators that were controlling their numbers. Those predators may have been really hindered or their populations really dropped during that heat wave, allowing Gambierdiscus to grow.”

“We’re trying to go back through the summer data and see if we can kind of reconstruct how we got here from there,” Parsons says. “It’s not an easy story to kind of put back together. So, it’s like looking for the evidence at a crime scene or something like that.”

“At some point, I would think, I would hope that nature is going to, you know, kick in and figure itself out,” Brame says. “That the fish stop being exposed to this, that whatever it is moves to a different environment, or they develop some immunity to it, or whatever the case may be,” he says. “But that nature would kind of resolve itself. And maybe we’re getting to that point, I don’t know.” ¦