Photograph: Mark Conlin / Alamy
Hundreds of coastal sharks have taken refuge in a Florida channel, apparently to escape the effects of a toxic red tide outbreak killing hundreds of tons of marine animals.
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Residents of Buttonwood Harbor on Longboat Key have recorded unusual footage of caphead, blacktip, nurse and lemon sharks swimming near their homes.
Florida has been fighting red tide epidemics for several years, caused by the algae Karenia brevis. This year’s blooms have been particularly large, according to marine biologists. The Florida Fish and Wildlife Commission (FFWC) reported fish deaths in the past week in nine counties and said five counties generated complaints of respiratory distress in humans linked to the red tide.
The FFWC reported high red tide levels off Longboat Key and around Sarasota. Experts say sharks seek a safe haven with food and oxygen, away from polluted water and rotting carcasses.
“Normally you don’t see sharks crammed together like that in these channels, they go there, but not in the huge numbers that we see reported,” said Mike Heithaus, shark expert and professor of biological sciences at Florida International. . University, and dean of its college of arts, sciences and education.
“We don’t know what the trigger might be for these sharks going to these areas, but the changes in the water chemistry, the oxygen extracted from the water, the toxins, combined with the amount of dead fish around, any of these could cause these large concentrations.
“It’s not the kind of thing you would see if it wasn’t for a great red tide.”
Longboat Key is a few miles from the site of a breach in the abandoned Piney Point fertilizer plant in April that saw tens of millions of gallons of toxic waste pumped into Tampa Bay. It is not known what impact the release could have had on the onset of the red tide.
Heithaus said the sharks in distress underscored the need for action.
“Seeing this stuff happening shows just how out of balance things are in the ecosystem right now,” he said.
“We really have to start working really hard in Florida to tackle some of the root causes of these blooms, too much nutrient going into the water, and it can come from a lot of different sources, so we really have to work on all of that.”
In 2019, Ron DeSantis, Governor of Florida, reactivated an algae bloom task force to look at issues related to the red tide.
The survival of Longboat Key sharks depends on factors such as oxygen levels in the canals, which can deteriorate rapidly as the water warms.
“If the conditions are really bad outside that channel, they could be blocked until the conditions reach the point where there is enough oxygen or there are no toxins coming out. they had to leave the canals, ”Heithaus said.
“But at the same time, if these conditions are heading south into the canal, there’s nowhere else to go. They can’t run if it’s not safe outside so it’s really hard to tell.