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Manatees making a lumbering return

For once, the news about manatees is good.

The aquatic mammals appear to be holding their own, despite a high rate of death from collisions with boats and loss of critical habitat.

Two 16-year studies show that the population of manatees in Florida waters, believed to be around 2,000, is remaining stable or possibly increasing slightly.

In recent years, scientists have believed the population to be declining, mainly because of the high death rate.

But scientists warn that the results are somewhat uncertain. And it would not take much to send the numbers in the other direction.

"The good news is that right now, the way the manatee biology is and the way human culture is, people and manatees ought to coexist nicely," said Stephen Humphrey, interim dean of the University of Florida's College of Natural Resources and Environment.

"But that's if things don't change," he said. "If things do change, it won't take much to get us into a crisis situation."

The studies, one by the University of Florida and another by the Florida Marine Research Institute in St. Petersburg, will be presented this weekend at the first international manatee conference in Gainesville. Both studies are based on 16 years of data, including studies of manatee carcasses, information about manatee birth rates and aerial counts of the mammals.

The UF study shows just how precarious the manatee population is thought to be. If just 15 to 18 more manatees die each year _ a mortality increase of 10 percent _ the animals will slide toward extinction.

That could happen. Injury from boat propellers kills about 50 percent of manatees that die each year. Biologists worry the problem will get worse as the number of people and the number of boats in Florida continues to increase.

Humphrey said current manatee-protection laws such as slow-speed zones and manatee sanctuaries are helping to keep the manatee population stable. But those laws are under pressure from boating enthusiasts, some of whom believe the laws are oppressive.

"If we pass boaters' bills of rights, if we repeal county boat speed zones, then the bad news side of this story will prevail," Humphrey said.

Some of the strictest rules are in place in King's Bay in Citrus County, one of the most popular gathering spots for manatees in the state. Nearly 200 manatees are often counted in the area during cool weather when manatees seek the warmer water of natural springs. But the rules there were put in place only after lengthy and heated debate.

Manatees also face danger because their aquatic habitat continues to be destroyed by water pollution and waterfront development. The animals are vegetarians and eat aquatic plants.

Bruce Ackerman, a biologist with the Florida Marine Research Institute, said his own analysis shows that the manatee population may have increased slightly during the past 16 years. But he warned that it's difficult to predict the future because trends are more easily recognized in hindsight.

"We can say we're pretty sure about what was happening five years ago," Ackerman said. "But we can't say what's happening here now."

Ackerman has organized statewide aerial manatee counts in recent years to get a better handle on the population.

The weekend conference will address a wide range of topics, including radio tracking methods, DNA analysis, brain behavior, feeding behavior and rehabilitation. The conference will be Friday through Sunday at the Gainesville Radisson Hotel and is open to the public.

_ Information from the Associated Press was used in this report.