Sharks take refuge from red tide in Sarasota Bay, Longboat canals

On Longboat Key, residents can see a few species of sharks looking for easier breathing far from the bay.

By Nat Kaemmerer
| 2:31 p.m. July 21, 2021

Sharks are congregating in waters with more oxygen for them to breathe.

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Sharks from Sarasota Bay are crowding the waters of some Longboat Key neighborhoods in an attempt to get a breather from red tide.

There are hundreds of sharks in the canal, said Jack Morris, Mote Marine Laboratory and Aquarium’s senior biologist in the Sharks and Rays Research Program. After getting a few calls from residents on the east side of Longboat Key, he went to investigate along Buttonwood Drive. He’s seen four species: blacktip, bonnethead, lemon and nurse. Normally, these sharks don’t venture into canals, because there’s not a lot there for them to eat.

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“The presence of red tide is basically forcing these animals to actually seek refuge in areas that don’t have red tide,” Morris said. “Right now, that happens to be Buttonwood Harbor, Crane's Bayou and in that canal adjacent to it. They’re just kind of balled up into that area … It's not the optimal conditions for those sharks, but in the presence of red tide, that's probably the only safe place for them right now.”

Red tide can cause a decrease in oxygen in the water, so the sharks have left the bay to try to find some easier water to breathe. Morris said there are so many sharks in Buttonwood Harbor that they’re running into each other.

“The local community actually put air stones that are bubbling air into the waterway,” Morris said. “That's basically helping boost the oxygen content in the water, which could be another reason why the animals are actually seeking refuge into that area because they're actually getting higher concentrations of oxygen.”

Once red tide decreases, the sharks should find their way back into their usual habitats on the seagrass flats on the west side of Sarasota Bay and in deeper waters, where lemon and nurse sharks like to hang out. If you see sharks while they’re taking refuge, you’ll probably see bonnetheads and blacktips up near the surface.

Meet the new neighbors

Blacktip sharks: Often grows to 5 feet and is known by the black markings on the ends of its fins. Commonly found in warm waters of the world, including brackish coastal regions. Blacktips have been known to make spectacular leaps from the water when attacking schools of small fish. Often wary of humans, but have bitten people especially in the presence of other food.

Bonnethead shark: A relative of the hammerhead, the bonnethead is common in warm, coastal waters. Typically about 2-3 feet, but can be larger. Perhaps the only shark known to eat seagrasses in addition to crustaceans and other underwater animals. Not known to be aggressive or a danger to humans.

Lemon shark: Can grow to 11 feet and is named for its yellowish coloring. Found from New Jersey to Brazil. It feeds often on smaller undersea creatures and is not considered a threat to people.

Nurse shark: Considered slow and sedentary, nurse sharks have bitten humans possibly because of inexperienced divers' inattention to their pokey outward appearance. Can grow to 10 feet. Mostly feeds on crustaceans, small fish and rays

“I'm assuming that we probably have equal numbers at the surface as we do below that line, so it's probably pretty packed with animals right now,” Morris said. “And sharks aren't the only things that are there … I'm sure rays and things of that nature have got to be in there as well.”

Morris advised against swimming in canals. Some of the lemon sharks are up to five or six feet, a size that can do some serious damage with a bite. If they get bumped, the lemon sharks will take a chomp. There are so many that even a quick dip invites a bite.

“These animals are so thick like that, if you fall in, I swear to God, you're going to hit probably five sharks,” Morris said. “It's most prevalent in the morning there at the surface, at least the bonnetheads are. I feel like I could run across the canal on the backs of the sharks.”