Swimming against disease Mystery: Scientists are trying to discover what's causing a lung infection that has killed scores of manatees off Florida since March.

April 24, 1996|By Dail Willis | Dail Willis,SUN STAFF

Manatees have been on Earth about 45 million years, far longer than the humans who study them. But much about the prehistoric endangered sea cow remains shrouded from human view.

Now, scientists are probing a new mystery: What is killing so many of the manatees in southwest Florida? Since March 5, 149 manatees have died of an inexplicable lung infection.

"It's going to be a bad year for manatees," Beth Wright says gloomily. She coordinates the radio tracking of southwest Florida manatees for the Florida Department of Environmental Protection, and her husband, Scott, is the FDEP veterinary pathologist who is performing necropsies on the dead manatees in an effort to discover the cause of the die-off.

"To have such a high mortality -- it's scary," she says.

An annual aerial count found 2,639 manatees living along Florida's coast earlier this year. But the lung infection, as well as unrelated accidents and disease, have killed 248 this year, more than the 201 that died in all of 1995.

The fight to protect and preserve these endearing sea cows has spread far beyond their native Florida. Not since the California condor captured the American environmental conscience two decades ago has an endangered animal aroused such widespread affection and concern.

The manatee die-off is being studied by a variety of state, federal and international agencies, including the U.S. Department of Agriculture, a Dutch university, an ad hoc federal program, military researchers and several universities in Florida. Scientists are performing a necropsy on each dead manatee, studying tissue samples and testing the water, air and sea grasses in the animals' environment in an effort to isolate the cause.

So far, the deadly lung disease has appeared in only one of the two herds of Florida manatees, a herd that winters along the west coast of Florida from Charlotte and Lee counties north to Hillsborough County.

A second herd -- which includes Chessie, the manatee who caught the public's imagination when he migrated to the Chesapeake Bay two years ago and to Rhode Island last year -- spends the winter along the east coast.

But if the mystery disease is a threat to manatees, a bigger threat to their continued existence is human activity.

Coastal development kills the sea grasses and other plants eaten by manatees, who must consume between 4 percent and 11 percent of their body weight each day -- that's five to eight hours of eating. The slow-moving, curious manatees also get wounded by boat propellers and entangled in crab pot lines and plastic trash in the ocean.

So pervasive are these injuries that the resulting scars are the basis for identification systems used by both Florida and the National Sirenia Project -- the scar tissue on the manatees is white and stands out so starkly against the gray skin that identification can be made visually from a distance or by photograph.

The National Sirenia Project is federal program based in Gainesville, Fla., that studies and tracks manatees.

Some manatees have been crushed or drowned by locks and gates along coastal waterways, and modifications to the design of such structures are being developed.

Complicating matters is the manatees' own biology. They reproduce slowly, taking two years or more to produce a single calf. The mortality rate in calves is high -- another manatee mystery.

Manatees in Florida -- they are properly known as West Indian manatees and their Latin name is Trichechus manatus latirostris -- migrate north each year in varying distances. Most of them stay south of Virginia, although one -- Sweet Pea -- was found near the outfall of a Texas power plant last year. Because they require water temperatures of 68 degrees or higher, manatees often are found near power plant discharge sites -- so much so that several electric companies have set up manatee observation stations for the public around Florida.

And scientists now are waiting to see what Chessie will do this year. His trip last summer to Point Judith, R.I., is the longest recorded migration by a manatee but some experts say that there may be others that we don't know about.

"I think it probably happens more than people realize," Ms. Wright says.

"As long as they can find a suitable habitat, there's no reason for them not to travel."

"All the verifiable accounts [before Chessie] don't extend past Virginia," said federal researcher James P. Reid of the National Sirenia Project.

Manatee carcasses have washed ashore in Virginia, he said, and the diaries of Capt. John Smith three centuries ago describe what appear to be manatees in the Chesapeake, as do references by earlier explorers.

But history, radio telemetry, satellite tracking and sonic beacons can't fill in all the blanks posed by manatee migration. Why do they travel? Why do some stay in north Georgia and others go farther afield?

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