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Sonar Device May Prevent Manatee-Boat Collisions

By John Roach
for National Geographic News
July 17, 2003
 
Researchers are developing a sonar system to help boaters steer off a collision course with the Florida manatee (Trichechus manatus Linneaus). The technology could be the difference between population growth and decline in the endangered species.

In 2002, 95 of the 305 recorded manatee deaths resulted from boat collisions, making it the leading cause of death for the slow-moving animals. The remaining manatee population is estimated to be less than 3,300, according to conservation groups.



The mammals, also known as sea cows, ply near-surface waters in coastal rivers, bays, and estuaries where they graze on marine grasses and other water plants. Manatees have light gray to dark rounded bodies that can grow up to 14 feet (4.2 meters) long and weigh as much as 3,000 pounds (1,361 kilograms).

Like deer in the headlights of an oncoming car, manatees have poor avoidance strategies when in the path of danger. Their natural instinct is to imperil themselves, said Jules Jaffe, a research oceanographer with the Scripps Institution of Oceanography at the University of California, San Diego. As a result, the manatees often get killed.

"They are very slow moving animals and when they sense danger the actually do the wrong thing—they migrate to the middle of the channel and surface," said Jaffe, who in collaboration with Ann Bowles, a senior research biologist at the Hubbs-SeaWorld Research Institute in San Diego, is developing a sonar system that would warn boaters of a manatee's presence and hopefully prevent fatal collisions.

The project is supported by a joint research grant from the National Geographic Society Conservation Trust and SeaWorld & Busch Gardens Conservation Fund.

"Manatees are totally at a disadvantage in Florida waterways," said Patti Thompson, director of science and conservation at the Save the Manatee Club in Maitland, Florida. "Boats are bigger and faster and there are many more of them than there used to be, so it has become an almost overwhelming problem for the manatees."

Thompson reviewed proposals submitted to the Florida Fish and Wildlife Conservation Commission to reduce the number of boat-caused manatee deaths. She said Bowles' project was the most promising of the lot.

Bowles "has the right idea for what it is we should be looking at when it comes to avoiding manatees," said Thompson.

The commission and the Florida Marine Research Institute have also provided funding for this project. Thompson said that it was the only one proposed that placed the onus of avoiding a collision on the boaters instead of the manatees.

"To expect animals that didn't evolve with the threat of boats to be the entity of the two that has to learn to avoid the boat, I think is an unfair expectation," said Thompson. "What we should do is discover a technology that allows boats to avoid manatees."

Manatee Finder

The researchers envision the manatee finder as a sonar system attached to a floating platform with a warning light on it that flashes whenever it detects the presence of a manatee. The targeted range for the finder is 200 to 500 feet (60 to 150 meters). If the technology is proven robust, it may be designed for use on moving boats.

One of the key challenges of the technology is to distinguish the manatees from logs and other debris in the shallow water, said Jaffe, who is leading the bioacoustic engineering for the project. Manatee habitat is mostly shallow, narrow, and grassy waterways.

"We have very little knowledge of the properties of sound in these kinds of environments," said Jaffe.

As part of their work in Florida, the researchers will characterize the environment to determine what signals come from the manatees and what other noise they will need to filter out in order to make the system effective. Otherwise, boaters may find the warning light to be unreliable and ignore it, said Jaffe.

"If we can get it to work in shallow water, then it can be active 24 hours a day and doesn't matter what the manatee is doing," said Bowles.

The researchers also want to make sure that the sonar is not a nuisance to the manatees or other marine animals. The sonar that will be used emits a low-powered signal that is said to be well above the manatees' level of hearing. Jaffe said he hopes the sound will also be above the hearing range of most dolphins and other marine animals.

"You have to be sensitive to all the marine animals and the problems they face," said Thompson. "That is why it hasn't been done yet. It is not easy, it is a challenge, but sooner or later we will hit on the right technology."

Thompson said this system is potentially effective in open coastal waters, where it is impractical to expect boaters to drive at slow speeds all the time. If effective, Jaffe said it could be in place within a few years.

Editor's Note: The manatee sonar project is one of two projects funded through a joint conservation initiative of National Geographic and Busch Entertainment Corporation to address urgent conservation concerns. The initiative was announced July 16. The second project, a study of wild lions in Kenya's Masailand and an investigation into what can be done to help livestock farmers protect their herds without having to kill the predators, is featured in a separate report published by National Geographic News. A list of recent stories about research supported by the National Geographic Society may be found at the bottom of this page.

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