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Dolphin deaths prompt close watch of red tide

Published Monday, November 29, 1999, in the Miami Herald

PHIL LONG
plong@herald.com

With cold weather just around the corner and hundreds of manatees moving south into the warm waters of Florida, marine scientists are carefully watching the movement of red tide along the Gulf Coast.

In a three-month period this fall, 70 dolphins were found dead in Florida along the northeastern Gulf of Mexico. The deaths occurred during outbreaks of red tide, an algae bloom in which plants give off a deadly toxin.

"It is disturbing," said Gregory Bossart, a marine mammal veterinarian and associate professor of pathology at the University of Miami.

Three years ago, an unusual late-winter red tide bloom in the Gulf and near-shore waters between Naples and Fort Myers killed nearly 150 manatees.

"It was the largest die-off of an endangered species ever," he said. The manatee population in Florida is estimated at about 2,500 to 3,000. There are tens of thousands of Atlantic bottlenose dolphins. Besides living in the ocean and the Gulf, they are plentiful in Biscayne Bay and other Florida estuaries where they feed on the bountiful crop of fish.

Dolphins often frolic in the shallow water and occasionally play in the wake of yachts and fishing boats. They have been thought to be immune from the effects of red tide because they generally swim away from infected areas.

DEATH TOLL RISES

So people are worried about what's happening with the dolphins this year. From August through mid-September, 34 dead dolphins washed up near Port St. Joe Bay. From mid-September through late October, another 36 were found along the coast from Panama City-Appalachee Bay through Fort Walton Beach and Destin. It is possible many more died and their bodies just sank.

Researchers also found dead fish, sea turtles and birds in the areas nearest the red tide.

"We have never had this many dolphins die like this," said Blair Mase, a Miami-based marine biologist and southeast stranding coordinator for the National Marine Fisheries Service, a federal agency.

"When you go from three to five a year up to 70 in three months, that's a lot," Mase said.

RELEASE OF TOXINS

Red tide is a naturally occurring algae bloom caused by tiny organisms that release brevatoxins, a poison that affects animals that ingest or inhale it, or eat creatures poisoned by it. It sometimes kills the animals.

There was a significant red tide in the Gulf near the Panhandle, with moderate to high levels of brevatoxins, Mase said.

"We have not been able to figure out how the deaths are related," Mase said. The dolphins might be eating fish poisoned by red tide; the poison might be getting into their respiratory systems -- the way it got to the manatees.

So far, the dead animals have been so decomposed that Bossart has been unable to get a good enough tissue sample to test for the poison, he said. Bossart's research was credited with cracking the manatee mystery deaths and linking them directly to red tide.