As big as they are, you'd think they'd be easy to spot. But in the mazes and murky waters of the Everglades, conducting a health assessment of the aquatic mammals isn't easy.

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WHITEWATER BAY, Fla. — It took three escapes, four hours, a couple of hundred dizzying circles from the spotter plane and too many turns to count by the capture boat.

Finally, the elusive creature splashed in the net: a Florida manatee.

The lumbering sea cows inhabiting the Everglades aren’t really any speedier or wilier than manatees elsewhere. But mazes of mangrove islands and water the color of café Cubano have long made their movements and numbers here a mystery to scientists.

“The Everglades region is the black hole. This is really the area where we don’t understand manatees,” said James Reid, a U.S. Geological Survey biologist. Reid led the team that corralled seven sea cows in Everglades National Park recently to assess their health and fit them with electronic tracking gear.

The captures and rapid releases wrapped up a seven-year survey designed to assess the effects of Everglades restoration on manatees, including the question of whether changing future water flows could harm them. The research also could shape decisions about slow-speed zones for park boaters and about the manatee’s controversial status as an endangered species.

From the 10,000 Islands south of Naples down to Florida Bay, the vast brackish Everglades backwaters represent the largest chunk of undeveloped manatee habitat in the state, and the least studied.

While scientists can’t yet answer the key question of how many manatees the Everglades supports, they have tracked them everywhere from estuary to ocean. One day, they might munch coastal sea grass — and the next, slurp freshwater miles up inland creeks.

“They get so far back in there you wouldn’t believe it,” Reid said.

“Difficult to study”

For more than 20 years, scientists have estimated Florida’s manatee population with aerial surveys conducted after winter cold fronts push the weather-sensitive sea cows into warm havens — particularly discharges from coastal power plants. That makes it relatively easy to count bobbing bodies and identify individuals from the distinctive scars left by boat props.

But monitoring manatees in places like Whitewater Bay, an expanse north of Flamingo most park visitors never see, poses considerable challenges.

“We have a lot more questions because we don’t have active thermal refuges where they aggregate,” said Catherine Langtimm, a USGS researcher developing aerial survey techniques and population models for the area. “It’s shallow, remote and difficult to study.”

Anglers and kayakers often encounter manatees in the park, usually when animals stick up their snouts and offer a leisurely snort. But scientists need more than snapshot moments to build reliable population studies. They need to know what, when and where they eat; whether they’re healthy; how long they hang out and how long they live.

To find their elusive quarry, the capture crew — scientists, veterinarians and graduate students from the USGS, the park, the Florida Fish and Wildlife Conservation Commission, several counties and the University of Florida — had to rely on an eye in the sky.

Biologist Lori Oberhofer, who joked that her “cast-iron stomach” won her the job of going aloft in a small spotter plane, pinpointed a group of manatees gorging on shoal grass near unnamed islands.

As the aircraft droned in a banking loop overhead, a slow-speed chase was on. From her vantage point, Oberhofer radioed a stream of directions, following a faint trail the crew aboard a special 24-foot capture boat kept losing in the murky water — boils of water and billows of mud kicked up by the manatees’ broad tails.

“Is that it, right at your one-two just off the bow?” Oberhofer radioed. “It looked like it was just laying there.”

“No contact,” Reid radioed. The animal, topping a half-ton and 10 feet — twice as long as the water was deep — was somehow invisible.

Oberhofer: “Nobody is moving away. There, nose up at your four.”

Catching the animal was nearly as difficult as seeing it. Three times, the target slipped away before the boat could encircle it with a net. On a fourth try, nobody was sure they had one until haulers felt a strong tug in the net.

“We couldn’t see squat,” said Reid, as a dozen people hovered over the young male.

Keep dousing the patient

Picture a scene from “ER” but with everybody wearing swimsuits and the patient being periodically doused with a jug of water. They marked and measured, taking snips of skin, drawing tubes of blood and collecting urine in a small plastic Frisbee.

Veterinarians constantly monitored its vitals, delivering extra oxygen when needed — a necessity because of the pressure the manatee’s bulky body places on lungs and organs when out of the water.

“You’re taking an animal that breathes very calmly in water,” said Mike Walsh, a veterinarian with the University of Florida’s marine mammal health program. “You put him on a deck and he can’t take as full a breath.”

The heartbeat, at 72, and lactic acid were a bit elevated by the chase, but overall, this was a healthy specimen — about 9 feet and 700 pounds.

“Here at the end of the summer, he’s in good body condition,” Reid said.

In half an hour, the manatee — the 29th researchers have tagged in the southern Everglades — was swimming away, visible only when the newly fixed satellite tracking buoy popped to the surface.

Throughout Florida, the estimated manatee count has hovered at 3,000-plus for a decade. Despite increases in fatal collisions with boats, which annually account for about a quarter of all manatee deaths, state and federal wildlife agencies are pushing to reclassify the manatee from an endangered species to the less-severe designation of threatened.

Developing a clearer picture of manatee health and numbers in the Everglades is particularly important because researchers believe the area holds the most manatees and it also is where they consider manatees most in trouble.

The Southwest population, an area extending from Florida Bay to Tampa, has been considered in decline due to the effects of red tides, cold snaps and boat collisions. That’s one reason Everglades National Park is weighing new slow-speed protection zones as part of a new management plan.

But Reid acknowledged the decline is largely based on data collected from populated coastal areas, not the isolated Everglades.

The mammals captured this year appeared healthy. Six of seven displayed one striking difference from relatives elsewhere: Their backs were largely unblemished by prop scars. The only one with significant scarring spent most of its time to the north in the busy waterways of Fort Myers.