Genetic Uniqueness Threatens Florida Manatee's Future

November 12, 1998

GAINESVILLE -- As Florida manatees lumber into warmer waters this month for their winter respite, they're admired for their unique appearance and lovable charm. But it's that very singularity that University of Florida scientists say could be leading the gentle sea cows down the path to extinction.

Genetic testing and DNA comparisons of manatees from eight regions along the Western Atlantic have revealed that the animals living in Florida waters share dangerously low genetic diversity, making them more susceptible to diseases and more sensitive to climate changes, said Brian Bowen, a conservation geneticist with UF's Institute of Food and Agricultural Sciences.

"What we've learned is the Florida manatee is genetically unique, and that it's isolated from manatees elsewhere in the Caribbean and the Yucatan," Bowen said. "Because of their low genetic diversity, it causes concern but not alarm. It's the same sort of problem that the Florida panther faced 50 years ago."

Researchers collected blood, skin and tissue samples from manatees in Florida, South and Central America, Mexico and the Caribbean. The DNA fingerprinting allowed scientists to gain valuable data on their population structures, said Angelica Garcia, a UF graduate researcher working with the Sirenia Project, a federal agency that studies manatees.

Because the manatees living in Florida make up a closely related, separate population, it means their numbers will rise and fall on their own.

"If the population crashes, they are gone," Garcia said. "It is unlikely that it will recover from a natural source of animals coming into Florida to repopulate."

By looking at the genetic traits of the manatee, biologists now believe a small number of Caribbean sea cows colonized Florida waters in the last 10,000 years. With only a few ancestors to start with, today's manatees could be faced with inbreeding problems, making it harder for the species to cope.

Despite the manatee's ability to swim large stretches of water, the populations tend to stay put because of their dependence on specific habitat features. The vegetarian animals prefer protected coastal waters and rivers, where seagrasses or fresh water vegetation are abundant, said Bowen, who is supervising Garcia's research.

"It's very much against their well-being to travel across open water." Bowen said. "Out there, they are big, slow and tasty. We think they are just a big shark egg roll, and that's one of the reasons they don't move much between their different habitats in the West Atlantic."

With probably 2,000 to 3,000 manatees left in Florida, Bowen said the population still is healthy, but their population trend must be watched closely.

"We have to watch them, and if we see a downward trend, then additional protective measures will be justified," he said.

Scientists with the U.S. Geological Survey, which is funded through the U.S. Department of the Interior and headquartered in Gainesville, believe that Florida manatees have a reasonable chance of surviving for another 1,000 years if human-related mortality can be controlled and habitat protected.

"The keys to manatee conservation are in the collection of accurate information on population and environment trends and effective law enforcement," said Robert Bonde, a biologist with the Sirenia Project.

The leading causes of death among Florida manatees are human-related, Bonde said. These include collisions with boat propellers, entanglement in float and fishing lines, and ingestion of foreign objects, such as garbage thrown from boats.

"It's critical that boaters slow down when they travel in manatee zones," he said. "It's also critical that we protect the manatees' habitat. For example, the seagrasses that they feed on are very susceptible to reduced light levels, which can be caused by pollution and fertilizer run-off."

Although it may be too late for the Florida panther, manatee researchers said that by informing the public and policing the waterways, there still is hope for the sea cow.

"The bad news for the Florida manatee is that they're on their own," Bowen said. "They're not going to get help from neighboring manatees in their plight to survive and persist in Florida.

"The good news is that we know about it before it's too late."
-end-


University of Florida

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