Hoping to help the endangered manatees recover from the threat of extinction, marine biologists brought three of the hefty sea cows raised in captivity to new lives in the wild.

The trio was released into the tea-colored waters of the mangrove swamps in Everglades National Park after living in the clear-water tanks at the Miami Seaquarium, raising worries about their chances.But officials were cautiously hopeful after Tuesday's release.

"It's an interesting mix: an older female capable of calving going out with two younger males," said Jim Valade, manatee recovery coordinator with the U.S. Fish and Wildlife Service. "It will be interesting to see if they stick together or how that mix is going to wash out, so to speak."

Instead of their daily diet of lettuce and other fresh vegetables at Miami Seaquarium, Aurora, Foster and Noah will have to learn to survive on sea grasses and other native vegetation.

The Florida manatee grows to about 12 feet and weighs up to 500 pounds. A plant-eating distant relative of the elephant, manatees are found in the bays and rivers of Florida, Mexico, Belize and northern South Am-er-ica.

But their numbers are dwindling: About 2,500 remain, and a record 415 deaths were counted in 1996. A record was set for human-caused manatee deaths last year, when 217 manatees died.

Since they often float near the surface, manatees often become victims of speeding boats with sharp propellers. Many also die from toxins.

The three newly released manatees are considered high-risk because two were born in captivity and one spent most of his life away from the wild.

Aurora, born during an aurora borealis nine years ago, is the first manatee to be released after being born and giving birth in captivity.

Five-year-old Foster, Aurora's brother, was set free once before in 1995 but was recaptured six months later, 200 pounds lighter and suffering from cold stress syndrome, a life-threatening con-dition.

Four-year-old Noah was rescued as an orphan three years ago after his mother's lungs were torn out by a passing powerboat.

Biologists will track the three manatees by satellite.