Searching for a scientific solution - Manatee Mortality

Boat/US Magazine, May, 2003 by Ryck Lydecker

Peering through an underwater glass viewing port at Florida's Homosassa Springs State Park, I'd have to be at sea for a very, very long time to mistake this creature for one of those beautiful half-fish women of maritime lore who could instantly make me forget life in the fo'c'sle or grant my three fondest wishes.

Yes, legend has it that Christopher Columbus referred to them as mermaids when he saw his first manatee in 1493 in what is now Cuban waters. There really is an endearing quality to this thousand-pound-plus hunk of marine mammal as I watch it grab floating heads of lettuce to nosh just below the surface. It's easy to see why the officially endangered Florida Manatee so captivates humans.

So I push the button to "hear the manatees talk" and a strange chirping sound comes from the speaker, not at all the bellow or groan you'd expect from a distant cousin of the elephant. But scientists are hoping to use the propensity of manatees to chat among themselves as one way to help ensure the continued comeback of the "sea cow" in Florida waters.

Technology Talks

"We call that vocalization," says Dr. Elsa Haubold who oversees what is termed "manatee avoidance technology" investigations for the Florida Marine Research Institute in St. Petersburg.

"Researchers have developed voice recognition software that can distinguish manatee vocalizations from other sounds in the water," Haubold explains. "The hope is that with a hydrophone army underwater coupled to this system, we could detect manatees in a given area. The system could then alert boaters to the animals' presence, perhaps using an automated buoy with a warning light or something like that."

The research, being conducted by four separate contractors with grant money from the Florida Legislature via the institute, is one approach to developing technology that could lessen "boat-manatee interactions" from the manatee's point of view, Haubold says. Additional projects using see-in-the-dark infrared cameras and heat-sensing thermal imaging technology, as well as sonar similar to that used in fishfinders, could lead to onboard devices that would detect manatees in the path of a vessel.

Several projects show promise, Haubold says, particularly the underwater eavesdropping approach. Although its useful range is limited thus far and background noise, particularly competition from Florida's ubiquitous snapping shrimp, poses a challenge, work is continuing for a second year.

Less promising is the application of infrared cameras since water absorbs most infrared radiation. Thermal imaging appears limited since the animals are so well insulated with blubber that body heat is difficult to detect.

Work on the sonar device is delayed pending the issuance of permits for field-testing as required by the federal Endangered Species Act and the Marine Mammal Protection Act. But this project, being conducted at Hubbs-Sea World Research Institute in Orlando, is another example of attempts to adapt off-the-shelf technology to improve the ways humans and manatees share the Sunshine State's waterways.

Both boaters and environmentalists agree that technology deserves a fair trial in the quest to reduce collisions between watercraft and manatees that last year resulted in the deaths of 95 animals.

In the hope of finding new answers, the Florida Legislature in 2000 appropriated $200,000 per-year for manatee avoidance technology, a move strongly advocated by Boat U.S. The initial goal is to minimize boat-manatee collisions.

The institute is also supporting the work of Dr. Edmund Gerstein at Florida Atlantic University in a separate $100,000 grant to develop two boat-mounted underwater signaling devices that would warn manatees of an approaching vessel. The devices should be completed later this year. (See "Sound Technology Deserves a Hearing" Boat U.S. Magazine, March 2000.)

The 40% Solution

Among the eight causes of manatee deaths cataloged by the institute, boat collisions have accounted for an average of 25-30% of manatee deaths annually even as the yearly counts of these animals grew from roughly 1,500 to over 3,000.

The "undetermined" category accounted for about 20% of last year's 305 manatee deaths. Other causes of deaths like ingesting debris, vandalism and poaching accounted for just under 3%, and incidents like crushing in locks or floodgates and entanglement in nets, accounted for about one-half of 1%.

That leaves roughly 42% of deaths attributable to nature, including cold stress, perinatal incidents and diseases like red tide, which killed over 200 manatees during severe outbreaks in 1982, 1996 and last year.

Red Invaders

"It's very likely that manatees have always been affected by red tide," reports Leanne Flewelling, a phytoplankton ecologist at the Florida Marine Research Institute. "Red rides normally occur in late summer or early fall but when we get large blooms in the spring while manatees are moving out of their wintering areas, that's when the effects --the numbers of deaths -- really stand out."