Sharks take refuge in Florida canal as red tide outbreaks continue to strike Florida

Chasing Sharks – Courtesy: Shutterstock – Image by Matt Reston

Hundreds of coastal sharks have migrated to a Florida canal, taking refuge to escape the catastrophic effects of a toxic red tide outbreak that has already killed hundreds of tons of marine animals. 

Buttonwood Harbor residents on Longboat Key have recorded strange footage of blacktip, bonnethead, lemon, and nurse sharks swimming near their homes.

Outbreaks of red tide are caused by the algae Karenia brevis and have impacted Florida for several years. Marine biologists say that this year’s blooms have been particularly significant. According to the Florida Fish and Wildlife Commission (FFWC), fish kills occurred in nine different counties while five counties reported respiratory irritation suspected to be related to red tide.

High concentration levels of red tide have been reported around Sarasota and off Longboat Key. Experts say the sharks are attempting to get away from polluted water and rotting carcasses, seeking a safe haven with food and oxygen.

“You just don’t normally see sharks piling up like that in these canals, they do go in there but not in the huge numbers that we’re seeing reported,” said Mike Heithaus, a biological sciences professor and shark expert at Florida International University.

“We don’t know what the trigger might be for those sharks going to those areas, but the changes in the chemistry of the water, the oxygen being pulled out of the water, the toxins, combined with the amount of dead fish around, any of those could cause these big concentrations,” he continued.

“It’s not the kind of thing that you would see if it wasn’t a big red tide event.”

Scientists fearfully anticipated a large bloom after the Piney Point phosphogypsum stack dumped wastewater rich in nutrients directly into Tampa’s waters back in April. Longboat Key is a few miles away from that site, however, it is still unknown what impact the discharge may have had on the red tide outbreak. 

Heithaus emphasized the importance of taking action after the sightings of the distressed sharks.

“Seeing these kinds of things happen just shows how out of balance things are in the ecosystem right now,” he said.

“We really need to start working very hard in Florida on addressing some of the causes of these blooms, too much nutrients getting into the water, and that can come from lots of different sources, so we really need to be working on all of it.”

In 2019, Florida Governor Ron Desantis reactivated an algal bloom task force to study the issues related to red tide outbreaks.

The Longboat Key shark’s survival depends entirely on factors such as oxygen levels within the canals, which can diminish quickly as the water warms up.

“If the conditions are really bad outside that canal, they might be stuck until the conditions get to the point where there’s enough oxygen or there aren’t toxins if they were to leave the canals,” Heithaus said.

“But at the same time, if those conditions go south in the canal there’s nowhere left to run. They can’t run if it’s not safe outside so it’s really hard to say.”

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