Hundreds of coastal sharks have flocked to a Florida canal in what experts said is an effort to take refuge from a catastrophic algal bloom that has wreaked havoc on ocean life in the region.
In recent weeks, canals in Buttonwood Harbor, near Sarasota, have been teeming with sharks, including bonnethead, black tip, nurse and lemon sharks, leaving area residents stunned.
“You literally could have walked across the canal on the backs of sharks — that’s how many there were,” Longboat Key resident Janelle Branower told WFLA-TV.
Red tide outbreaks, which are caused by the Karenia brevis algae, have been an issue on Florida’s west coast for several years. The organism occurs naturally in ocean water, but runoff from human activities can provide excess nutrients for the algae. That pollution, coupled with warming waters tied to climate change, can lead to uncontrollable algal blooms that kill marine organisms.
According to conservation groups, this year’s outbreak has been particularly devastating. Dolphins, manatees, turtles and hundreds of tons of dead fish have piled up on shorelines.
The sharks are likely seeking sanctuary in the canals away from the polluted ocean water, experts said.
“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,” Mike Heithaus, a shark expert and biological sciences professor at Florida International University, told The Guardian.
Scientists are concerned that the heavily-packed waterways will be depleted of resources for the sharks before the red tide subsides.
“If there’s not enough oxygen, they will overexert themselves trying to get fresh water over their gills so they can exchange their CO2 for oxygen. But with all those animals packed in that space, oxygen is limiting,” Mote Marine Laboratory senior biologist Jack Morris told FOX13 Tampa Bay.
If the red tide lasts for long enough, Morris said, the sharks could “run out of food and energy and unfortunately some of them, if not all of them, will die.”
The area is several miles from the defunct Piney Point fertilizer plant, which experienced a significant spill in April that saw hundreds of millions of gallons of wastewater pumped into Tampa Bay. It’s not yet clear whether the breach exacerbated the algae outbreak.
In 2019, Florida Gov. Ron DeSantis (R) started the Red Tide Task Force as part of his administration’s efforts to mitigate the blooms in the state. Local communities and conservation groups have called on DeSantis to do more to combat the ecological crisis, including declaring a state of emergency.