Environment

Waters off Florida Keys hit with rare red tide. It’s prime suspect in fish kills.

University of Miami spokeswoman Diana Udel collected dead fish earlier this month after spotting them west of Marathon.
University of Miami spokeswoman Diana Udel collected dead fish earlier this month after spotting them west of Marathon. Courtesy Diana Udel

A rare red tide has spread across waters off the Florida Keys, likely triggering numerous fish kills reported by anglers.

Florida Fish and Wildlife Conservation Commission scientists began tracking Karenia brevis, the algae that makes up red tide, in southwest Florida north of Monroe County several months ago. On Feb. 19, they reported elevated levels near Sandy Key on the western edge of Florida Bay.

Red tide can kill fish, cause respiratory problems and make shellfish dangerous to eat.

red tide map
Earlier this month state wildlife officials reported a rare appearence of red tide in western Florida Bay near Sandy Key. Florida Fish and Wildlife Conservation Commission

Wind and current likely carried the tide from the north, said FWC spokeswoman Michelle Kerr.

Over the last month, anglers reported seeing large fish kills, although it’s still not clear the algae killed the fish, that included grunts, small eels, trout and cowfish, along with bigger barracuda and ladyfish. The dead fish were spotted west of Marathon and from Sandy Key to Islamorada. Commercial fishermen and guides, already struggling after Hurricane Irma slammed the Lower Keys, were not taking the news well.

“These guys are coming off the hurricane where some of them had their houses damaged,” said angler Dave Preston, who fished an Islamorada fly tournament for redfish and snook last weekend. “Half the hotels are still closed and now they have this to deal with.”

Red tides typically appear further north, between Tampa and Naples, fed by polluted water flowing off land or flushed from the Caloosahatchee River, said University of Miami Rosenstiel School of Marine and Atmospheric Science marine biologist Larry Brand.

50 year red tide map
Biologist Larry Brand has documented 50 years worth of red tide records and found that most have occurred between Tampa and Naples. Larry Brand University of Miami Rosenstiel School of Marine and Atmospheric Science

The algae, which turn the water red, occur naturally in ocean water but can bloom into dangerous concentrations under the right conditions. Over the last 50 years, Brand said the tides have become 15 times denser, fed by Florida’s swelling population.

“You just keep dumping all these nutrients on your continental shelf and a lot of that ends up in the sediments,” he said.

At their worst, red tides can kill wildlife that consume the algae and cause muscle spasms or paralysis. In 2017, state wildlife officials blamed red tide for a spike in manatee deaths.

It’s possible Hurricane Irma, which drenched the state and generated heavy flooding, helped spur the tide. In 2004, after four hurricanes hit the state, the west coast was coated with a red tide, he said.

State wildlife officials are continuing to monitor the bloom and will provide an update Friday, Kerr said.

Follow Jenny Staletovich on Twitter @jenstaletovich

  Comments