Abnormal fish event in the Keys leaves scientists scratching heads

Several species of fish in the Florida Keys are exhibiting strange spinning behavior in the same area where a small-scale fish die-off is occurring.

Since the fall of 2023, the Florida Fish and Wildlife Commission has received more than 500 reports of abnormal fish behavior in the Florida Keys, the islands that push south from the tip of the Floridian Peninsula. More than 52 species of fish are reported to exhibit a strange “spinning” behavior, including the critically-endangered Smalltooth Sawfish.

Descriptions of the behavior include that the fish “swim in circles at the water’s surface” and have lost their ability to “stay upright when exposed to bright light at night,” according to the National Oceanic and Atmospheric Administration (NOAA). Several fishes exhibited the spinning behavior before dying.

Sawfish look like sharks and are part of a family of species that include rays and sharks, and they have a long flat snout with teeth along the edges.

Even more puzzling than the event itself: Scientists studying the behavior cannot figure out the cause, having ruled out more common culprits such as red tide.

Some scientists have located high levels of neurotoxins within the gills and livers of affected fish. Others, such as Ross Boucek, the Florida Keys Initiative Director, are now looking into factors such as water quality and algae as an influence.

“I think the ultimate cause is, you know, how we manage our waters here in the Keys,” Boucek told the News Watch by phone. “Whether or not we have enough evidence to say this is a direct result of bad water is too early to say, but the toxins were definitely in the water. That's for sure.”

Boucek noted an unusually high amount of a kind of sea-dwelling algae known as Gambierdiscus. Boucek described this algae as a “semi-microscopic little plant and animal combined that for whatever reason decides to spit out toxins into the water.” Gambierdiscis often comes from reef systems though they can also be highly prevalent in seagrass systems.

“Usually when this species becomes a problem, or balloons up in an area or becomes elevated, it’s a result of some kind of human or environmental impact,” Boucek said.

Boucek believes an extreme heat event that occurred two months before the spinning fish began being reported could be correlated to the flare-up of Gambierdiscus in the water. 

“When we had this heat wave where this event started, there was this weird secondary effect of this brown water algae bloom that caught everybody off guard,” he said.

There have been seen similar Gambierdiscus reactions to external stimuli in places such as the Pacific Islands during World War II. After multiple reefs were destroyed by bombs during the conflict, many civilians became sick with ciguatera poisoning.

“It seems like when you disturb the environment, this is one of the things that comes in there and takes over for a bit,” Boucek said. “So it only makes sense, you know, based on where it started, where we saw the brown water, and what that probably did to the small fish communities that would eat this stuff normally.”

One of the leading inspirations to find the culprit of this strange phenomenon is the impact it has on the critically endangered Smalltooth Sawfish. There have been a total of 54 sawfish mortalities due to this event, according to the Florida Fish and Wildlife Conservation Commission.

Though the exact number of remaining Smalltooth Sawfish is unknown, the International Union for the Conservation of Nature estimates there could be as few as 200 adult sawfish in the world.

“I mean, the sawfish has been around since the dinosaurs and we have so few, so to be potentially down 30% to 50% is, I mean, that is huge. It's really sad,” Boucek said.