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. Even Columbus noted their distinct lack of beauty when he first saw them in the New World in 1493. But while manatees have no natural enemies, their population is dwindling (total today is just over 2,000). Some of their deaths are from disease, pollution, pleasure boat collisions and boat propeller wounds. But a surprising number of deaths are also caused because manatees have no fear of Florida's underwater canal gates and locks. Each year a significant number of manatees die after being crushed in the canal locks.
The Navy is helping to change that last statistic, however. Funded by the Office of Naval Research, last March a system of acoustic sensors - originally developed by ONR for underwater mine detection - was 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. Using the technology of the acoustic sensors developed by ONR, the Harbor Branch Oceanographic Institution in Fort Pierce, Florida developed 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. This protection is provided while either one or both gates are moving. The sensors are fully functional 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. Currently, engineers are now preparing to install the system at the H.H. Buckman Lock in Palatka, Florida.
"The underwater acoustic imaging technology utilized here was originally developed for the detection and disarming of undersea explosive mines," says ONR 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. Part of Florida's Manatee Protection System, this program was funded by ONR through its Small Business Innovation Research Program. Taylor's team developed the program using piezoelectric acoustic sensors made by Materials Systems, Inc. of Littleton, Mass.