“Ultimately, boat noise does fall into their hearing range and there might be some other factors that are really kind of the main issue of them not detecting or telling where those boats are coming from,” said Joseph Gaspard III, Mote’s manatee care, training and research coordinator. “Water depth lays a large role…even what kind of sediment -- sand vs. mud. So, there’s a lot of components working against that sound transmitting and getting to the animal.”

Earlier research has shown manatees may have trouble locating where a sound is coming from. But part of the answer could also be what manatees spend the majority of their time doing: sleeping and eating.

“They might be masking the sound with their chewing which is an ongoing thing,” said Gaspard. “They could even tune themselves out. And also, when they’re sleeping, they prefer to rest in shallower waters which unfortunately does not give a manatee sitting on the bottom and a boat traveling on the surface. There’s kind of game if inches between those two elements if they’re in the same vicinity.”

The hearing study was published April 12 in the Journal of Experimental Biology.

Gaspard says touch is probably a manatee’s primary sensory system. Mote’s ongoing touch sensory study will be published in the journal Marine Mammal Science. Gaspard says these sensory studies could help wildlife officials design better policies to protect manatees in the future.