Tampa, Fla. — The gentle sea cow, which lives in the coastal waters and canals of Florida, is facing a new threat.
Easy to catch and hard to miss, these amiable manatees have survived hunters looking for meat and hides, and power boats, which injure the manatees with their propeller blades.
But in the last five weeks, 24 dead manatees have been found, and they were neither shot, speared, nor run over.
With only about 1,000 manatees left in Florida, the rising toll worries scientists, especially when the cause of death is unknown. Some are concerned that if whatever is causing the death of the manatees spreads to other areas where they congregate, the sea cow could face extinction.
Manatees are slow-moving, vegetarian mammals, ranging in size from 8 to 15 feet long and weighing up to a ton. They live throughout Florida and Caribbean waters. Every winter the Florida populations congregate in warmer inland waters, often near power plants that discharge hot water.
''It's very unusual to have 24 manatees die in a few weeks, especially when the cold is not a factor,'' says Pat Rose, who has been studying the manatees for the past five years as a researcher for the Florida Audubon Society.
''My first hope is that the dying stops,'' he says. ''My second hope is that we determine what's killing them. I'd rather have them stop dying right away and never know what killed them.''
The United States Fish and Wildlife Service found 114 of them dead in 1981, an unusually high figure that was blamed on cold weather. Another high death rate this year could put more stress on the manatee's slim population, says Dave Peterson, manatee coordinator for the service.
A Fort Myers, Fla., resident found the first victim on Feb. 5. He was boating near the mouth of the Caloosahatchee River and spotted a huge carcass floating in the water. He reported the find to the Florida Marine Patrol, which picked up the body for study.
During the next weeks, more and more bodies appeared in San Carlos Bay and the Caloosahatchee River. Each one was recovered and taken to the US Fish and Wildlife Service laboratory in Gainesville, Fla., for study.
''They came one at a time,'' says Kathy Beck, a biological technician in the service's laboratory. ''Some days we might get two or even three, but they were spread out fairly evenly for more than a month.''
By the end of the third week in March, the death toll stood at 24.
Scientists are trying to perform autopsies to determine the cause of death. But no cause has been determined yet.
''We're checking for toxins, pollutants - anything that might have killed them,'' Ms. Beck says.
Samples have been sent to four different laboratories around the country, she adds, and results are not expected for weeks.
Cold weather has been ruled out as a reason, she says. Manatees are susceptible to cold, and if they cannot find warm water during the coldest days of winter, they die. But the weather around Fort Myers was warm during February, and the approximately 140 manatees who congregated around Florida Power and Light Corporation's Tice power plant in the winter had begun to roam in open water again.
That raised the red tide to the top of the list of possible reasons for the manatees' death. Red tide is a mass of small organisms that create a reddish-colored poison that contaminates shellfish and kills fish. Red tide had infested San Carlos Bay at the time. Tests to check on the red tide's possible impact have not been completed yet.
''We know of no other cases where the red tide killed a manatee,'' Ms. Beck says. ''I don't see how it could kill one. Manatees are vegetarians, and they wouldn't feed on contaminated mollusks.'' As air-breathing mammals, manatees should not be susceptible to red tide poison, she says. Fish are killed when they filter the poison through their gills.
The manatee is a popular animal among Floridians, many of whom take a personal interest in its protection. And the Florida Department of Natural Resources is running radio advertisements asking anyone who spots an ailing manatee to call the department's manatee hotline.
Scientists are worried that whatever is killing the manatees will spread to other parts of the state.
''So far it seems to be localized in one area,'' Mr. Peterson says. ''If what's killing them is transmittible, it's possible that it could spread from one location to another. That could make one heck of a severe dent in the population.''