Science

Hundreds of sharks take refuge in western Florida canal after fleeing toxic red tide

Hundreds of sharks in West Florida have headed inland to escape the deadly red tide that’s killed more than 600 tons of marine life in the region.

Different shark species, including bonnethead, blacktip, nurse and lemon sharks have been spotted darting through Longboat Key and into the canals of Buttonwood Harbor, far from their usual habitat.

‘You saw fins at first, just popping up,’ resident John Wagman told WFLA 8. ‘Just something I’d never seen in the canal before.’

Reports of marine predators in the bay started surfacing last week.

‘You could literally walk across the canal on the backs of the sharks in the water,’ resident Janelle Branowner told FOX 13 Tampa Bay. ‘We don’t have healthy water in the bay right now.’

The sharks are invading the area because their usual habitats in Tampa Bay, Sarasota Bay and along the coast from Pasco to Sarasota Counties, have been infested with red tide, which is caused by unusually high blooms of the algae Karenia brevis.

The algae kills marine life by producing a potent toxin that affects their central nervous system.

It ​​can also cause respiratory problems for humans, and has polluted the water, lowered oxygen levels and filled waterways with fish carcasses.

An usually rampant ‘red tide’ in west Florida caused by an algae bloom is forcing sharks to look for safe haven in a inland canal near Longboat Key

A red tide appears on Florida’s Gulf Coast about once a year, but these natural events are becoming more rampant, experts say, with climate change warming waters and allowing the microscopic algae population to flourish.

The red tide has been ‘patchy and persistent since December 2020,’ according to Mote Marine Labs, but the bloom has recently increased in severity.  

Last week, the Florida Fish and Wildlife Commission (FFWC) reported massive fish kills in nine West Florida counties.

Five counties reported complaints by humans of respiratory distress related to red tide.

In the first half of 2021, officials have cleaned up more than 600 tons of dead fish caused by the red tide

In the first half of 2021, officials have cleaned up more than 600 tons of dead fish caused by the red tide

Water samples from Pinellas County, which includes St. Petersburg and Clearwater, show concentrations of red tide up to 17 times greater than the level considered high.

While scientists have yet to find a ‘smoking gun’ for the unusual blooms, Longboat Key is only a few miles from the abandoned Piney Point fertilizer plant, where a breach in April saw millions of gallons of toxic discharge dumped into Tampa Bay, according to The Guardian.

Bonnethead (pictured), blacktip, nurse and lemon sharks have all been spotted in Longboat Key, far from their usual habitats in Tampa Bay, Sarasota Bay and along the coast from Pasco to Sarasota Counties

Bonnethead (pictured), blacktip, nurse and lemon sharks have all been spotted in Longboat Key, far from their usual habitats in Tampa Bay, Sarasota Bay and along the coast from Pasco to Sarasota Counties

Water samples from Pinellas county show concentrations of red tide up to 17 times greater than the level considered 'high'

Water samples from Pinellas county show concentrations of red tide up to 17 times greater than the level considered ‘high’

Hiding out in the canals is a stopgap measure, experts warn.

‘If it goes on long enough, they’re gonna run out of food and they’re gonna run out of energy,’ Jack Morris, senior biologist at Mote Marine Labs and Aquarium, told WFLA. ‘And unfortunately some of them, if not all of them, will die.’

The name ‘red tide’ comes from the fact that overgrowth of algae can cause the color of the water to turn red, as well as green or brown.

City officials say this summer is the worst red tide they have seen since 2018, when a bloom spread nearly 145 miles and killed larger animals like manatees and dolphins.

Since the 1990s, there have only been four summertime blooms in the area: one in 1995, another in 2005 and, most recently, in 2018.

Hundreds of manatees have already died this year due to algae blooms destroying the seagrass beds they eat to survive.  

A red tide is a large 'bloom' of toxic algae that appears on Florida's Gulf Coast about once a year. These natural events are becoming more rampant with climate change warming surrounding waters and allowing the microscopic alga population to flourish. Pictured: The region of West Florida affected by red tide blooms in summer 2021

A red tide is a large ‘bloom’ of toxic algae that appears on Florida’s Gulf Coast about once a year. These natural events are becoming more rampant with climate change warming surrounding waters and allowing the microscopic alga population to flourish. Pictured: The region of West Florida affected by red tide blooms in summer 2021

The Florida Fish & Wildlife Conservation Commission reported that 841 manatee deaths were recorded between January 1 and July 2, breaking the previous record of 830 in 2013 after an outbreak of toxic red tide.

Earlier in July, marine biologists with Mote attempted a novel approach to tackling red tide: Partnering with Woods Hole Oceanographic Institute (WHOI) and the University of Central Florida, they sprayed wet clay to kill algae cells and toxins, a strategy used around the world to combat toxic similar blooms.

According to a statement from Mote, dry clay is mixed with seawater to create a ‘slurry’ that is hosed over the infected water.

As the dense clay particles sink, they combine with red tide cells—hopefully killing them as they bury them in the sediment on the seafloor.

‘This is just the first of what we hope will be several upcoming trials of clay flocculation on active blooms in the wild,’ WHOI scientist Don Anderson said in a statement.

‘What we learn here will help us better understand how conditions in Florida affect its success and how clay flocculation might be tailored to blooms of Karenia brevis, as well as other species of algae, here and elsewhere in the world.’


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