animals are hit repeatedly by boats

Researchers at Florida Atlantic University have laid the groundwork for a sensory explanation for why manatees and other animals are hit repeatedly by boats. Last year, 73 manatees were killed by boats in Florida’s bays and inland waterways. Marine authorities have responded to deaths from boat collisions by imposing low speed limits on boats.

In spite of manatee protection policies that have been in effect for nearly two decades to slow down boats passing through manatee-protection habitats, the number of injuries and deaths associated with collisions has increased and reached record highs.

In an effort to reduce manatee deaths and injuries from boats, Dr. Edmund Gerstein, director of marine mammal research and behavior in FAU’s Charles E. Schmidt College of Science, set out in 1991 to investigate what might be the underlying cause for these collisions. Gerstein disagreed with the unsubstantiated assumptions, which wildlife officials had relied upon, that manatees could hear boats, but they were just too slow and could not learn to avoid boats.

“Manatees have the cognitive prowess to learn and remember as well as dolphins and killer whales,” said Gerstein. “Furthermore, when startled or frightened, manatees explode with a burst of power and can reach swimming speeds of up to 6.4 meters per second in an instant.”

Given that manatees have the cognitive ability to recognize danger and the physical prowess to evade boats, Gerstein sought to explore the answers to some simple questions. “After a manatee has been hit more than once (some have been hit up to 50 different times) why doesn’t the animal learn to get out of the way?” “Is it possible that manatees are not aware or cannot hear the sounds of an approaching boat?”

Gerstein and his colleagues conducted rigorous, controlled underwater psychoacoustic (audiometric) studies to understand what sounds manatees can hear in their environment. After a comprehensive series of hearing studies, his research revealed that manatees cannot hear the dominant low frequency sounds of boats and that those sounds do not transmit well in shallow water. Furthermore, ambient noise in manatee habitats can conceivably mask the perception of many kinds of signals. Unlike dolphins, which can use active sonar to navigate and detect objects in the environment, manatees are passive listeners restricted to listening to their auditory landscape.

morevia sceicnceblog