Between June and early July 2017, one fish kill in Monroe County was reported to state wildlife officials.
During the same time frame this year, more than 40 have been reported.
“Yes, that is a high number of reports for any specific area in a short amount of time,” Michelle Kerr, spokeswoman for the Florida Fish and Wildlife Research Institute, which tracks fish kills, said in an email Wednesday.
The good news: Florida wildlife officials don’t think it’s part of a red tide or other type of algae bloom plaguing other parts of South Florida. The bad news: Even longtime Keys people can’t remember a worse string of kills than this one.
Officer Bobby Dube of the Florida Fish and Wildlife Conservation Commission has been stationed in the Keys since 1989. Asked if there were ever this many fish kills in Monroe County in such a short period, he replied, “Not that I can remember.”
The species of dead fish being reported to the Florida Fish and Wildlife Research Institute’s database include mullet, pinfish, minnows and other baitfish, sharks, tarpon, parrotfish and yellowtail snapper, and also lobster and eel.
No part of the Keys has been spared, but areas including Islamorada and Key Largo in the Upper Keys, and Summerland Key in the Lower Keys have been affected most, according to FWC records.
Kerr said FWC scientists conducted water tests on June 27 off Plantation Key in Islamorada and Big Pine Key in the Lower Keys, which came back negative for algae blooms and red tide, although elevated levels of Karenia brevis, the algae that makes red tide, were reported in Florida Bay in February and thought by Keys anglers to be behind fish kills reported in late winter.
Red tide algae occurs naturally in the ocean, but can form blooms dangerous to sea life, especially when fueled by on-shore pollutants and farm runoff.
What state scientists did find this time were low dissolving oxygen levels close to 0 milligrams per liter, “which can lead to fish kills,” Kerr said.
The problem is particularly severe in canals and basins where water doesn’t flow regularly. Kerr said decaying vegetation in Keys canals is likely making matters worse. She added that debris from September’s Hurricane Irma still in canals has not been linked to the problem.
Backcountry fishing angler and guide Mike Makowski, 42, thinks the root of the problem is a larger amount of sargassum weed in the water this summer, combined with warm water temperatures and low winds.
“As it decomposes, it sucks the oxygen out of the water,” said Makowski, who has been guiding clients on Keys flats with his Blackfoot Charters for 17 years.
Makowski said most of the fish kills he’s seen have been on the ocean side of the Keys, in small basins where water gets trapped. Small birds have been targeting these areas for easy meals.
“Anything swimming in that area is going to die,” he said.
Correction: The original story reported water test samples in the Keys determined low dissolving oxygen levels close to 0 milliliters per liter. Oxygen is measured in milligrams, not milliliters.