A manatee's entire face is about as sensitive as your fingertip, according to research presented at APA's 2011 Annual Convention by New College of Florida psychology professor Gordon Bauer, PhD. That's an important finding because it helps explain why the endangered Florida manatee so often gets ensnared in fishing nets, hooks and traps, said Bauer.
"Their strong tactile orientation may be at the root of their problem with fishing gear," he said. "It's how they investigate things."
Bauer and his colleagues tested two manatees' sense of active touch by presenting them with pairs of plastic plates with vertical grating, and rewarding them for selecting the one with the wider ridges. The manatees investigated the plates by rubbing them with their faces, which are covered in fine hairs, and the less sensitive manatee was able to distinguish between gratings that were just 0.15 millimeters apart—about one-tenth of the height of a grain of sugar. (The more sensitive manatee detected gratings just 0.05 millimeters apart.)
Motion-sensing hairs cover the entire body of the manatee, though they aren't spaced as closely on manatees' backs and bellies. The body hairs help manatees detect slight vibrations in the water, according to a second experiment by Bauer. In that study, Bauer blindfolded the manatees and muffled their facial hairs with a mask, then set a ball vibrating in the water. Using their body hairs only, the animals detected very slight vibrations between 15 and 150 hertz.
This highly developed sense probably helps manatees navigate by detecting the surface, bottom, current and objects in the water—though, unfortunately, it hasn't helped them steer clear of the motor boats that are decimating their population, Bauer said.