Epidemic Hits Rare Manatees : More than 120 have been found dead on Florida coast in what one scientist calls the ‘worst nightmare’ for the endangered species.

In the worst die-off of a U.S. endangered species ever reported, more than 120 manatees have dropped dead along Florida’s Gulf Coast in the past five weeks, triggering an intense international investigation to identify the mysterious killer.

Wildlife scientists have not ruled out any possible causes, but they suspect that the giant “sea cows” are dying either of an extremely virulent disease or from ingesting a toxin in red tide.

The grisly epidemic worries wildlife experts since the tropical walrus-like creatures are already in danger of extinction because of boat collisions and destruction of sea grasses in the shallow coastal inlets they inhabit.

“This is a very serious situation,” said Gregory Bossart, a pathologist at University of Miami School of Medicine who is participating in the investigation. “We managed to kill most of this species off, and now we have a natural mortality, coupled with man’s inhumanity to this species, that could be the final death blow. This is your worst nightmare for the manatee.”

As of Wednesday, the body count since the plague began March 5 had reached 128 in southwest Florida. Statewide, 221 manatees have died this year--about 10% of the rare creatures remaining in the nation, said Jim Kraus, assistant manatee coordinator with the U.S. Fish and Wildlife Service in Jacksonville.

More manatees have already perished in the past three months than have died in any single year, and the epidemic seems to be surging, not ebbing. Five were found dead in the 24 hours ending Wednesday evening.

“Hour by hour, additional animals are being discovered,” Kraus said.

The bodies were found along the 80 miles between Englewood, just south of Sarasota, and Marco Island, an upscale stretch of Florida’s Gulf Coast popular with tourists for its white sand beaches.

The dead animals are being examined by forensic experts and toxicologists at about a dozen laboratories, including experts in the Netherlands skilled in diagnosing a newly discovered distemper virus that has stricken some of the world’s dolphins and seals.

But even if the experts succeed in finding the cause, that doesn’t mean there will be a cure in time to save the manatees.

Like coroners conducting an autopsy, biologists are searching for virtually everything, from pesticides in brain tissues to natural toxins in stomachs and signs of infectious disease in blood cells.

The dead animals all have pneumonia-like purple lesions in their lungs, similar to those found in seals and dolphins that have succumbed to a contagious morbillivirus similar to canine distemper.

In the United States, no other species protected as endangered has suffered such a large and sudden die-off.

“We’ve had whales wash ashore, but nothing has ever approached this. This is truly a puzzle,” said Ken Burton of the Fish and Wildlife Service in Washington, D.C.

With two front flippers and bristly muzzle hairs, manatees are often called the ugly and underappreciated cousin of dolphins and whales. They can weigh half a ton, grow to 15 feet long and consume 100 pounds of seaweed a day.

Listed as an endangered species in 1967, even before the modern Endangered Species Act was adopted, West Indian manatees were one of the first animals in the nation to be protected because their numbers had been so severely depleted. They inhabit parts of the Gulf and Atlantic Coast south of North Carolina.

Florida Gov. Lawton Chiles called the deaths “a horrible tragedy.”

“I can tell you we have marshaled every available resource to help address the situation,” said Chiles, who attended a necropsy of one of the animals Monday.

Six federal agencies have teamed with the state, including the Centers for Disease Control and Prevention, as well as two universities, the Miami Seaquarium and Seaworld.

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The die-off is the first major test of a new team of government and academic experts, called the Unusual Marine Mammal Mortality Events Working Group, that was formed after the response to other die-offs was haphazard and poorly coordinated. In 1987, hundreds of bottlenose dolphins washed ashore on the East Coast, and years passed before experts learned the distemper virus was at fault.

In the wild, epidemics generally run like wildfire for weeks, decimating a population and then dropping off. But in this case, experts do not know whether it has peaked or just begun. Wildlife officials had thought the die-off ended March 18 because there was a brief lull, but it started again on March 27.

It may be weeks before a cause is isolated, despite the intense effort.

“We don’t have any definitive answers, but we’ve been investigating at least two areas more diligently than others. I would put a virus or a [red tide] toxin right at the top of the list,” said Bossart, who is also a veterinarian at the Miami Seaquarium.

Scientists wonder if a recent cold snap may have stressed the warmth-loving animals, leaving them susceptible to disease or red tide toxins.

In a red tide, algal organisms called dinoflagellates collect in sea water and can poison animals. Numerous fish and bird kills on the East Coast have been tied to toxic algae, which is believed to be a growing phenomenon worldwide because of the buildup of fertilizers and human wastes in coastal waters.

A severe red tide has hovered off southwest Florida this year, and has poisoned cormorants and fish. But the classic signs of such illness are absent in the manatees and preliminary tests of their digestive tracts have been negative for the usual toxins. They appeared to be well-fed, healthy adults before they were stricken.

If only a few manatees remain alive in the wild, the limited gene pool could mean eventual extinction. Florida wants to avoid the crisis of the California condor, which vanished from the wild and was reintroduced only after years of a rigorous captive breeding program.

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Power boats that slash the slow-moving manatees with their propellers have been the creature’s biggest killer. Florida has invoked some speed limits in harbor areas and a 15-square-mile manatee sanctuary was created near the Kennedy Space Center in 1990.

The gentle giants belong to the group of mammals called sirenia, named after the seductive sirens of lore. But while many Floridians enjoy petting them at marinas and drive cars sporting “Save the Manatee” license plates, more charismatic animals get far more attention.

“I think the manatee suffers a form of species discrimination,” Bossart said. “People identify with animals with certain sex appeal. If you had only 2,900 dolphins left and they were being run over by boats, I would guarantee you there wouldn’t be boats out there anymore. But manatees are on the low end of the list.”