Lingering red tide leads to more fish kills, manatee injuries

Rick Bartleson, a research scientist for the Sanibel Captiva Conservation Foundation pulls a water sample from the Caloosahatchee River that will be tested for red tide.
Rick Bartleson, a research scientist for the Sanibel Captiva Conservation Foundation documents shoal grasses in the Caloosahatchee River on Thursday 12/8/2016. He and members of his crew also pulled water samples to test for red-tide.  Red tide has been found in patches throughout Lee County.
Rick Bartleson, a research scientist for the Sanibel Captiva Conservation Foundation documents shoal grasses near the mouth of the Caloosahatchee River on Thursday. Bartleson and his crew are responsible for red tide testing in parts of Southwest Florida. Higher counts of Karenia brevis has been documented in parts of Lee County resulting in fish kills.

Rick Bartleson drops anchor in the Caloosahatchee River, grabs his snorkel and slithers into his full-body wetsuit, one still wet from the previous day's swim.

"We're having fish wash up on the beaches and some black drum," he says, with a northeast wind whistling in the background. "They're in spawning season, and a patch of red tide went across them. Sometimes that happens to mullet. They get in huge schools near passes, and that can get them killed."

This year's red tide started at the beginning of November and has been found from Tampa Bay to the Fort Myers area since. Some areas show low to background traces of Karenia brevis, the organism that causes red tide here.

Red tide bloom intensifies off SWFL

Bartleson, however, collected a sample Monday that showed 1 million Karenia brevis cells per liter of water, a concentration high enough to be detected by satellites.

Fish kills can happen when concentrations reach 10,000 cells per liter. Higher levels have killed off hundreds of manatees in Lee County in a matter of months.

A manatee showing symptoms of red tide poisoning was pulled from local waters by wildlife officers last week and taken to the Miami Seaquarium.

Karenia brevis occurs naturally but nutrient-laden waters washing off the local landscape can increase the duration and intensity of red tide blooms, scientists say.

Fishermen are reporting dead black drum as well.

"On the way in we noticed hundreds of floating objects and originally thought they were buoys," said local offshore commercial fisherman Abdiel Marin. "We passed by a close one that appeared to be a little bigger than a buoy so we turned (toward) it and to our horror found it was the rotting corpse of a dead adult black drum. We then realized what we saw the whole way in was dead fish, most of which were spawning-sized adults."

Marin said he's having to go farther and farther into the Gulf of Mexico to find clear water and decent fishing. Last year, he said, he traveled about 15 miles offshore but isn't seeing clear, fishable waters until he's 25 miles or so offshore. The extra distance means extra fuel costs and more work hours, and Marin said he fears he may soon have to quit fishing if water conditions don't improve.

Red tide counts high along SWFL coast

Fish kills have been documented in the Matlacha and Pine Island Sound areas in recent weeks, and spurts of dead fish continue to wash up on local beaches.

The Florida Fish and Wildlife Conservation Commission collects red tide data for the state and posts regular updates. Maps released Thursday show counts of up to 1 million cells per liter near the south end of Sanibel Island and the north side of Fort Myers Beach, which are to the north and south of the mouth of the Caloosahatchee River.

Counts in Pine Island Sound were lower (1,000 to 10,000 cells per liter) while measurements taken in Bonita Springs and the Naples area show only background levels.

Connect with this reporter: Chad Gillis on Twitter. 

Red tide

Karenia brevis, cells per liter

1,000 to 10,000: Shellfish harvest closures, possible respiratory irritation in humans and other mammals

10,000 to 100,000: Respiratory irritation, fill kills possible and bloom may be dense enough to be detected by satellites

100,000 to 1,000,000: Fish and marine mammal kills more likely

Over 1,000,000: Same as above plus possible rusty brown discoloration of water 

Source: Florida Fish and Wildlife Conservation Commission