Mote Marine and FWC staff respond to distressed smalltooth sawfish on April 5, 2024. This fish was given vitamins and antibiotics, tagged and released. At least 28 others have died in what one expert calls a “particularly complex puzzle.”
September 16, 2024
By Mike Conner
This abnormal behavior, spinning, has especially impacted the smalltooth sawfish (Pristis pectinata), an endangered species with a long, flat nose and sharp, chainsaw-like teeth. The affected sawfish swim in circles, spinning (or whirling) and thus far at least 40 species other than sawfish have been observed exhibiting the same behavior, primarily on inshore waters of the Lower Florida Keys. A number of the symptomatic fish have died, according to the National Oceanic and Atmospheric Administration (NOAA).
At press time, scientists hadn’t yet fully explained what’s affecting these fish. As of late spring 2024, some 50 dead smalltooth sawfish had been documented, though the toll may be higher, because the bodies of these fish typically sink when they die.
A total of 109 smalltooth sawfish have been observed spinning, including the 28 that ultimately died.
Early Observations Documented Bonefish & Tarpon Trust (BTT) and the Lower Keys Guides Association (LKGA) first received reports of fish in the Lower Florida Keys exhibiting abnormal behavior in November, 2023. The fish apparently lose equilibrium, causing them to swim upside down in circles repeatedly. BTT and LKGA have since received a total of 57 reports of symptomatic fish.
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Numerous species, including silver mullet, tarpon, permit, snook, pinfish, ballyhoo, jack crevalle, southern stingray, goliath grouper, redfish, lemon shark, Atlantic sharpnose, smalltooth sawfish and others have been affected.
Symptomatic fish have been observed more frequently at night. The episodes seem fairly localized with approximately 77 percent of reports coming in from between Bogie Channel and Bow Channel in the Lower Keys, though some are from west of Key West. And, a few fish have exhibited spinning near Miami, north of Biscayne National Park in Biscayne Bay.
Harmful Algal Blooms team at Florida Fish and Wildlife Research Institute works to identify sources of the event. High levels of Gambierdiscus have been found. Collaborative Study Led by BTT and LKGA, an inter-institutional collaborative research study to identify the cause of these symptoms began on January 11, 2024. Florida International University’s Fish Ecology Lab, University of South Alabama, Florida Gulf Coast University, Woods Hole, Florida Department of Environmental Protection, and Florida Fish and Wildlife Conservation Commission (FWC) are involved.
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In this collaborative study, scientists are looking at various contaminants and synthetic compounds, harmful algal blooms in the water column, benthic (sediment) harmful algal blooms and overall fish health.
BTT and LKGA have coordinated and executed sampling events to collect symptomatic fish and paired water samples. BTT and LKGA have collected 40 symptomatic fish, and 15 surface water samples. FGCU has collected 132 benthic samples. No sampled fish showed virus or parasites or any organ abnormalities. No red tide was detected and FL DEP did not detect common contaminants.
But one finding in the benthic harmful algal blooms samples identified elevated concentrations of the dinoflagellate in the genus of Gambierdiscus co-occurring in areas where symptomatic fish are.
Gambierdiscus produces ciguatoxin, which can bioaccumulate in predatory fishes and result in ciguatera poisoning in humans who consume fish over reefs that are environmentally stressed. The stress is often reflected in algae overgrowing coral and reduction in coral cover.
At this point, scientists cannot call the concentrations of Gambierdiscus the culprit behind these symptomatic fish, or whether this particular dinoflagellate is producing toxin that moves up the food web only affects fish through gill absorption. Testing is ongoing. According to Dr. Aaron Adams, BTT Director of Science and Conservation, the most affected fish are bottom dwellers.
“The Gambierdiscus typically attaches to bottom algae, whether on the flats or nearby shallows, so fish there are especially vulnerable, if in fact this dinoflagellate and its toxins are causing the behavior,” said Adams. “And just because we confirm that a toxin or toxins are being produced, we can’t assume that is what’s behind this. It’s a particularly complex puzzle right now.”
Impacts to Humans The Florida Fish & Wildlife Conservation Commision is collaborating in the investigation, and says all fisheries in the Florida Keys that are open, remain open. Swimming where the affected fish are is not recommended.
A Heat Wave Connection? The 2023 summer heat wave was the most intense on record for South Florida. The Conch Key region saw fish kills in mid-July and BTT received 59 reports of either dead fish, poor water quality, or dead living bottom habitat, directly attributed to hot water.
In early October 2023 guides and commercial fishers began observing fish lose equilibrium and “spinning” when exposed to a stimulus such as a beam of light at night. Crawfish bully netters were among those making early reports to FWC. By late January sawfish began showing these behaviors, stranding themselves on shorelines and perishing.
“As far as the heat wave and its possible effect, one has to consider that the entire Keys and South Florida marine ecosystem is not in great shape, given seagrass loss, land-based pollutants, fish full of human pharmaceuticals and more,” said Adams. “If it were pristine, you can bet it would be more resilient to stressors and adverse impacts, such as abnormally high water temps. Could it be that this loss of resilience allows for such ‘outbreaks’?”
The Smoking Gun? Benthic (bottom sediment) assessments identified extremely high concentrations (6-10 times higher than 14-year average abundances) of the toxic benthic dinoflagellate Gambierdiscus in areas where fish spinning reports are most frequent.
Assessments of toxins present in symptomatic fish and toxins produced by this specific “bloom” identified Maitotoxin, a novel variant of ciguatoxin, and Gambierones in both subjects. Maitotoxin is highly toxic and water soluble, allowing for exposure through gills and the potential to cause the acute behavioral responses seen in the Keys. The most recent testing has shown that multiple harmful algal species may have thrived following the heat wave.
Can Fish Recover? BTT is conducting surveys to evaluate whether sick fish can recover. To date, 66 fish have been used in recovery trials captured during five field days. This work shows that the duration of recovery varies by day and by tide. This temporal effect suggests that the stressor is acute and transient.
There is also significant variation in whether species show symptoms, and their duration of recovery. For instance, at the same location over multiple trials, grunts have not shown any symptoms. Sixty six percent of grey snappers showed symptoms, with recovery times averaging 13.5 minutes. One of 27 snappers did not recover.
Last, a new study is ongoing to provide causative evidence that the suite of harmful algae species in the Keys are eliciting these symptoms in fish. Algae pellets collected in the Keys waters were shipped to University of South Alabama, their toxins were extracted and laboratory raised zebrafish were exposed to them. After 20 minutes of exposure, the zebra fish developed symptoms similar to that of the Keys fish in the wild. Those symptomatic fish were then placed in control water and recovered within 30 minutes.
Public Input Bonefish Tarpon Trust has launched a weekly text message board platform enabling guides to answer questions reporting fishing quality, locations fished, where spinning fish were observed, and how intense were those observations. The response rate is over 90 percent with approximately 60 captains from flats, bay boat and offshore fleets participating.
As of May 22, there had been 50 sawfish deaths, the FWC has received 489 hotline reports of spinning fish, the Lower Keys Guides Association has seen over 180 symptomatic fish reports, and over 60 fish species have been reported as affected.
To report spinning fish or a fish kill, contact the FWC Fish Kill hotline at 800-636-0511.
This article was featured in the July 2024 issue of Florida Sportsman magazine. Click to subscribe .
