June 4, 2009—Manatees can't hear the low sounds of boat engines, which is why the animals are frequently injured, a researcher says. A high-pitched alarm could solve the problem.

Video by Public Television's Wild Chronicles, from National Geographic Mission Programs

Unedited Transcript

FLORIDA LOVES ITS MANATEES.

HERE IN CRYSTAL RIVER, ITS PRACTICALLY AN OBSESSION.

NEARLY EVERYWHERE YOU LOOK, THERES A MANATEE LOOKING BACK AT YOU

ON SHIRTS

ON BUILDINGS

AND EVEN ON LICENSE PLATES.

BUT DESPITE THEIR POPULARITY, TIMES ARE TOUGH FOR THESE LOVEABLE BEASTS.

RECENT SURVEYS SHOW THAT FLORIDAS MANATEE POPULATION IS STEADILY DECLININGAND TODAY THERE MAY BE LESS THAN 3500 LEFT IN THE WILD.

OF THOSE THAT REMAIN, FOUR OUT OF FIVE BEAR THE SCARS OF ENCOUNTERS WITH BOAT PROPELLERS.

BUT WHATS MOST PUZZLING IS WHY MANATEES DONT SWIM AWAY FROM THE NOISY MOTORS OF ONCOMING BOATS.

DR. EDMUND GERSTEIN HAS BEEN PUZZLING OVER THIS QUESTION FOR NEARLY THREE DECADES.

ED BEGAN TO UNRAVEL THE MYSTERY WITH THE HELP OF TWO CAPTIVE-BRED MANATEES TRAINED TO PERFORM SIMPLE TASKS.

Ed Gerstein: "We asked a simple question. Is it possible that manatees can't hear the boats, or if they can hear them they can't tell which direction they're coming from. So my wife and I actually set up a series of experiments to test the manatees hearing to see exactly what they could hear."

WHAT THE GERSTEIN'S DISCOVERED WAS ASTONISHING--- THE MANATEES SEEMED CONFUSED BY THE LOW-FREQUENCY SOUNDS MADE BY MOTOR BOATS.

BUT WHEN CONFRONTED WITH CERTAIN HIGH PITCHED SOUNDS, THEY RESPONDED ALMOST INSTANTLY.

Ed Gerstein: "What we found was that manatees have very good hearing but their hearing is at higher frequencies than what anyone expected. Actually the animals hear fairly poorly at low frequencies. And unfortunately for them, slow moving boats produce primarily very low frequencies."

NOW, AFTER NEARLY 20 YEARS OF RESEARCH, ED AND HIS WIFE LAURA HAVE AN INNOVATIVE IDEA.

COULD THEY DEVELOP AN ALARM THAT EXPLOITS THE MANATEE'S BEST HEARING ABILITIES? ED: Flash cards are in

NOW, ITS TIME TO PUT IT TO THE TEST

Buoy one is all set for deployment.

ED AND HIS TEAM HAVE SECURED SPECIAL PERMITS TO CONDUCT TRIALS IN THE RESTRICTED WATERWAYS NEAR NASAS CAPE CANAVERAL.

THE TEAM SETS BUOYS IN THE WATER EQUIPPED WITH UNDERWATER MICROPHONES AND DIGITAL SOUND RECORDERS.

BEING NATURALLY INQUISITIVE MANATEES SOON MOVE IN TO INSPECT THE BUOYS.

AND WHEN THEY DO, ED AND HIS TEAM APPROACH THEM IN BOATS.

THE DRIVERS ARE TRAINED TO PREVENT COLLISSIONS.

BUT WILL THEY NEED TO? THE BOATS ARE EQUIPPED WITH THE NEW ALARMS. THEY ARE EMITTING A HIGH PITCHED SOUND THAT ED BELIEVES THE MANATEES WILL HEAR.

As you can see, one cameras capturing the wide angle view.

BACK IN THE LAB, ED AND HIS ASSISTANT JOSIAH REVIEW VIDEO OF THE EXPERIMENTS.

NORMALLY, MANATEES WILL NOT MOVE TO AVOID A BOAT, UNTIL THE VERY LAST MOMENT WHICH IS OFTEN TOO LATE.

BUT WHEN EDS VESSEL SOUNDS THE ALARM, THE MANATEES REACTION IS CLEAR.

You can see the animal come into frame hereyeah look at thathe starts to orient at about, what would you say that is?at about 75 feet, 24 meters. Thats great. And now hes taking off rather quickly. This is a successful alarm runYeah, thats really goodYou can definitely tell how the animal reacts.

AGAIN,

AND AGAIN.

AND AGAIN.

ED: "We've got 17 alarm runs and for those alarms we got 100% reaction, the animals reacting way before the boat gets there. And we've got over 65 silent runs where 97% of the time the animals haven't reacted at all."

THE ALARM IS A SUCCESS.

ED HOPES THAT SOMEDAY, ALL BOATS IN MANATEE FILLED WATERS WILL BE EQUIPPED WITH SIMILAR DEVICES.

ED: "In a sense if we were to put this device on the boat which would be very inexpensive, only about $125, it's a user based tax that the boaters would gladly pay if they could put this on their boat and maybe get to an area a little bit quicker. And more importantly protect the animal as they're going."