Boat alarms may help save manatees
11/02/2009
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A Florida Manatee in the Homosassa River in Florida |
The gentle “sea cow” or Florida manatee (Trichechus manatus latirostrus) – a subspecies of West Indian manatee – thrives on aquatic vegetation in the spring-fed rivers and shallow marine and estuarine waters off of Florida, though they also occasionally venture into the Gulf of Mexico. Fewer than 3,500 of these endangered species remain in the wild, and one of their biggest problems is motor boats, which run into them and kill or injure them. Four of five living manatees have scars on their bodies from past boat strikes.
Conservation biologists have tried speed limits for boaters in certain areas, and have educated boaters and the general public for years about the possibility for collisions, but still the manatees die. They collide with even slow-moving boats. And therein may lie the problem.
Dr. Edmund Gerstein, Director of Marine Mammal Research at Florida Atlantic University, who has studied manatee-boat collisions since 1991, realized that the manatees may not hear the boats, especially those moving at slower speeds. Gerstein conducted a series of audiometric experiments with captive-bred manatees to test what frequencies and sounds these marine mammals hear and respond to best. Turns out manatees did not hear the very low frequency sounds – similar to a slow-moving boat propellor – but they did hear higher frequency sounds very well. Before this, wildlife officials assumed that manatees could readily hear slow-moving motorboats, but were unable to swim out of the way quickly enough. That didn't make sense to Gerstein who knew manatees could swim in bursts of speed up to 21 feet per second. His acoustic experiments turned that mistaken notion on its head, suggesting sound not speed was the key problem.
But even better, the results gave Gerstein an ingenious idea: boat alarms. Acoustic boat alarms would cost only around $125, a low enough cost to feasibly get installed on every boat in manatees’ nearshore habitat - particularly in murky waters where boaters cannot readily see the manatees. Gerstein tested the boat alarms in the wild near NASA's Cape Canaveral with huge success. Gerstein and colleagues approached manatees slowly in a boat using an alarm and 100% responded to the alarm, moving away from the boat, often at a full 75 feet away or so. In controls, in 65 "silent runs" with no alarms, 97% of the manatees did not move away from the boat. Such acoustic alarms have potential to help reduce boat collisions with whales in other locales, as I wrote about in my post, Technology Saves the Day (and the Whales).
"I believe the alarm can and should be used today, especially on slow moving commercial barges and other large vessels that are responsible for many of the watercraft related mortalities each year. Current speed laws have no impact on these large lumbering vessels and are essentially ineffective," says Gerstein. "For the Florida manatee, this device is proven to be effective and I hope that it will be adopted into a mandated protection strategy by the State so that manatees and recreational and commercial boaters can co-exist on the waterways."
The U.S. Fish & Wildlife Service just initiative a review of the manatee’s “critical habitat” under the Endangered Species Act, and information must be sent to them by October 29th - search regulations.gov for docket FWS-R4-ES-2009-0066. FWS last designated “critical habitat” for the manatee in 1976. This 90-day review is the first step in a process in which the FWS will determine whether a more extensive review is necessary. They define critical habitat as the geographical areas that have features the species needs for survival and reproduction.
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