Florida's giant manatees are curiously gentle sea creatures - whiskered, slow moving, and blubbery, with spatula-shaped tails, fingernail-tipped flippers, and thick gray skin. While manatees have no natural enemies, their population is dwindling - to an estimated Florida population today is just over 2,000. The activities of people are to a large extent responsible for this decline.
Some manatee deaths are from disease, pollution, pleasure boat collisions and boat propeller wounds - and by being crushed in underwater canal gates and locks. Each year, a significant number of manatees die after being crushed in the canal locks.
A product developed by the U.S. Navy is helping to change that situation. A system of acoustic sensors has been fitted onto the gates and locks at Port Canaveral. Designed to stay open if a manatee is near them, the Port Canaveral gates now operate like garage doors - sensing in a tenth of a second if a manatee is nearby. The gates will not close until the creature passes by. During the first five weeks of operation, the system detected seven manatees and saved them.
Historically, the only way to prevent manatee accidents at the Florida's gates had been to spot them visually - difficult to do in murky waters - and manually hold the gates open until they passed.
The system being used in Florida is a non-contact acoustic detection system that uses a ladder of sound beams between the two gates. The edge of one gate is fitted with a series of sound emitters placed at 20-centimeter intervals. Receivers that have been fitted onto the edge of one gate detect the signals being generated. Should a manatee be between the closing gates, the sensors detect it, activate audio and visual alarms and open the gates. The sensors can function in zero-visibility conditions.
The results to date? Not a single manatee death has occurred in any of the gate closings at the outfitted site since March, 2000. "The underwater acoustic imaging technology utilized here was originally developed for the detection and disarming of undersea explosive mines," says Office of Naval Research Program Manager Wallace Smith. "It's good to see a commercial civilian application of this Defense technology to protect marine mammals."
"The goal would be to eventually have all of Florida's canal and gate locks fitted with these simple sensors," says project engineer Larry Taylor of the Harbor Branch Oceanographic Institution.
