Hearing of Manatees May Prove to be Key to Protecting Species

The New York Times

Tampa, Fla.
At the flash of a hand signal in the water, Stormy, a 1200-pound, 7-year old manatee, swam to place his head in the wire hoop suspended in his tank. Seconds later, a light came on at the end of the tank, signaling that it was time to swim out of the hoop and bump his lips against a paddle suspended to the right of the light. When he responded correctly, his trainer blew a whistle that told him to collect his reward, a monkey biscuit.

The behavior Stormy was learning will soon be used to develop a manatee hearing test. Stormy will swim to insert his head in the hoop, and a tone will be sounded in the water. When the light comes on, Stormy will indicate if he heard the tone by swimming to the left paddle if he did and to the right if he did not.

Six months ago, Dr. Edmund Gerstein of Florida Atlantic University began Stormy’s training here at Lowry Park Zoo in Tampa. When Dr. Gerstein advances to the hearing test, he will be studying Stormy and another manatee, Dundee, to try to find out why nearly every manatee spotted in Florida’s waters seems to have collided with a boat. Could it be that manatees cannot hear approaching boats, so they are unable to swim out of harm’s way?

The research is part of an effort to protect manatees, seal-like marine mammals sometimes called sea cows, that grow up to 13 feet long and weight up to 3,500 pounds. Although they have been on the endangered species list for nearly two decades, protection programs have been slow to develop. Under a recovery plan for manatees that got under way in 1983, Federal and state officials are doing basic research to determine the life history and habitat requirements, and are taking steps to protect their habitats, reduce mortality and educate the public.

But no one can say for sure whether the plan will work. “We’re playing catch-up right now,” said Patrick Rose, the administrator of the Office of Protected Species in the Florida Department of Natural Resources.

Scientists say that at least 1,800 West Indian manatees roam the coasts and coastal rivers of Florida and southern Georgia, but, given the difficulty of spotting the animals under murky water, no one is certain how many there are, or whether the population is increasing or decreasing.

In 1991, at least 174 manatees died in Florida. Fifty-three of those died of injuries caused by boats, according to the Department of Natural Resources, which determines the cause of death in each case. The boat-related deaths set a new record, but just barely. The death toll has been climbing for several years, and scientists are not sure about how long the population can withstand such a high mortality rate.

“Right now it’s anybody’s guess whether the number dying exceeds the number being born,” Mr. Rose said. “Regardless of where the population is today, the animal’s ability to recover gets more difficult every day.”

“Some see the manatee as a warm, cuddly issue,” he said. But he added, “They are the barometer of how well we are able to protect coastal ecosystems. As the manatees fare, so do the systems.”

The research on the manatees’ hearing was originated by Geoffrey Patton, a senior biologist at Mote Marine Laboratory, a nonprofit research organization in Sarasota. He is collaborating with Dr. Gerstein.

“One manatee in Florida has been hit at least 12 times, judging from his scars,” Mr. Patton said. “Why don’t they learn to avoid boats?” he asked.

Mr. Patton and Dr. Gerstein say the solution may be to learn to warn the animals of oncoming danger. Once they determine the manatees’ hearing range, they will try to find out how well manatees hear in the presence of background noise and whether they can tell the direction of the  tone.

Looking for a Solution

“If we could determine their hearing ability, it may be possible to modify the sounds that boats make so the animals can locate them and get out of the way,” Mr. Patton said. “It could boil down to some simple plastic device on the hull that would vibrate at the right frequency and cue the animal.”

A few feet away from Stormy’s tank, two wild manatees were recovering from their injuries under the watchful eye of zoo volunteers. One had a collapsed lung that had probably been pierced by a rib broken in a boat collision. The other had been caught in a crab-trap line, which cut off the circulation in his flipper. Both are expected to recover.

The manatees of Florida, which are genetically distinct from a small population of manatees found in the Caribbean and South America, are protected under a state law that dates back to 1893, as well as by the 1972 Marine Mammal Protection Act and the Endangered Species Act of 1973.

During the 1970s, however, relatively little was done to help the manatees, primarily because of a lack of money, staff and commitment from both the Fish and Wildlife Service and the State Department of Natural Resources. Protection efforts increased in the 1980’s, but were still insufficient, so, at the urging of the Marine Mammal Commission, a Federal advisory group, a new recovery plan was written in 1989. In that same year, Florida established the Save the Manatee Trust Fund, which relies on the public to make donations and purchase special manatee license plates to finance the state’s programs.

One priority of the recovery plan is to determine the manatees’ life history and habitat requirements. Since the late 1970’s, scientists have conducted aerial surveys to estimate populations at specific locations, for example, near the warm water outfalls of power plants and the natural hot springs, where the manatees congregate in winter. But those surveys opened “only a very narrow window into their lives,” said Dr. Tom O’Shea, director of the Sirenia Project, the manatee research agency of the Fish and Wildlife Service.

Tracking the Manatees

The Federal agency and the state are now using tracking techniques that allow them to follow an animal continuously for weeks and months. About 20 wild manatees have been fitted with harnesses above their tails; a stiff tether extending from the harness holds a satellite transmitter above the water line. The electronic signals are picked up by satellite, enabling scientists to find out where these animals congregate and how long they stay there. That information, along with the findings from manatee carcasses and other data, is used to make decisions on which areas are essential to the manatees.

The service is also keeping track of 900 manatees that can be identified by the distinctive scar patterns left from their collisions with boats. Each winter, when the manatees congregate at warm water sources, biologists identify individuals, take photographs, and try to determine the condition and reproductive status of each animal. The information is used to gauge birth and death rates and habitat usage patterns.

The injured manatees at Lowry Park Zoo were being cared for under the recovery plan’s mandate to rescue and rehabilitate as many injured or diseased manatees as possible. Rescue teams transport injured animals to one of five ocean areas, like the Miami Seaquarium, where marine-mammal veterinarians try to nurse them back to health.

“Our goal is to release as many of those animals back into the wild as we can so they can reproduce naturally,” said Robert Turner, the manatee-recovery coordinator for the Fish and Wildlife Service. In May, three manatees were released at the Merritt Island National Wildlife Refuge, including a female who had been injured and her calf, which was born in captivity. Most released manatees are fitted with satellite harnesses so their progress can be tracked.

Although the survival rate for released manatees is good, Mr. Turner said, orphaned calves and rehabilitated manatees who have spent long periods in captivity may not know where to go or how to get food. “It’s like taking a pet and throwing it into the woods,” he said. To improve survival rates for such animals, the service plans to build a special pen at the refuge, sort of a halfway house, where manatees that are ready for release can become acquainted with wild manatees across the fence until they are ready to be turned loose.

The most controversial aspect of the manatee program is the attempt to slow boats down near manatee habitats. The Department of Natural Resources has set speed limits for hundreds of miles of waterways in nine counties and plans new speed limits for four more. The regulations, which are imposed after consultation with the counties, require boats to go very slowly in some manatee gathering spots and travel corridors, and they prohibit all human activities in some areas.

While manatee advocates endorse the plan, many waterskiers and boaters have fought the rules. In Sarasota County, speed zones were adopted last December, and signs were posted in the waterways in July. Even before the signs were posted, the County Commission had decided to review the regulations.

Rick Rawlins, owner of the Highland Park Fish Camp in Volusia County, says the rules adopted there last year would put him out of business because the slow-speed zones lengthened the time it took to reach fishing spots.

“The rules would add as much as five to six hours to a day of fishing,” Mr. Rawlins said. “My customers are leaving me. Some said they are not going to fish anymore. Others are going to other counties.”

Mr. Rawlins has formed a group called Citizens for Responsible Boating to fight the regulations. The group filed an administrative appeal with the state; when that was turned down, it filed suit against the Department of Natural Resources, arguing that the economic impact on local businesses had not been fully considered. That suit is pending.

The boat speed limits are not the final step. Each county is also required to develop a comprehensive plan for manatee protection. Each plan must address issues like controls on marina sites and other development.

Despite the increased efforts of recent years, no one is certain that the manatee will thrive in future years. “We’ll be able to tell something once the manatee-protection plans start taking effect,” Mr. Turner said. “If we start to see mortality decline, then I have good hope that we can do something. If, after all these efforts, we still see increases in mortality, I really don’t know what the next step will be.”

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