The Florida manatee is protected by both the Marine Mammal Protection and the Endangered Species Acts. These animals typically graze and travel alone, but are able to migrate to warm water in colder months and find other manatees to socialize and breed with. A January 2011 synoptic survey estimated the endangered Florida manatee population to consist of only 4,834 animals.
Unfortunately a large number of annual manatee mortalities are caused by people: the manatees are struck by boats, crushed in water control devices, and entangled in or consume fishing gear. Since the Florida manatee lives in a habitat where these threats occur regularly and other manatees are often out of visual range, it is important to understand how the manatee perceives and functions in its environment.
Animals know and navigate their world through their senses. They need to be able to detect key aspects of their environments, to process stimuli, and to react and adapt. However, people introduce stimuli (e.g., noise, chemicals, and turbidity) that have the potential to disrupt what animals perceive and how well they can react to their surroundings. Unless we know what manatees sense, or in some cases may fail to sense, it is difficult to develop effective conservation recommendations that can limit the damage people do to their habitat.
To this end, behavioral studies conducted with two captive-born manatees, Hugh and Buffett, cared for at Mote Marine Laboratory & Aquarium, in Sarasota, Fla., have generated detailed sensory biology knowledge over the last 13 years. Mote’s valuable partnerships with New College of Florida, the University of South Florida, and the University of Florida has facilitated undergraduate and graduate student assistance with training Hugh and Buffett for a variety of behaviors which have been incorporated into very specific investigations of their sensory processes including studies of visual acuity, passive and active vibrissae (whisker) touch, auditory frequency detection thresholds, auditory temporal processing rates, and sound localization.
Results from these studies have yielded a wide range of information that has greatly increased our understanding of how the manatee perceives its environment and reacts to environmental stimuli. It is only through the study of the animals in our care that we now know that manatee vision is extremely poor, however they have the ability to discriminate fine textures using their facial vibrissae. This suggests that manatees might give objects careful tactile scrutiny the way humans give objects visual attention, but this may also put them at risk as they spend a significant amount of time carefully and tactilely scrutinizing crab traps, fishing lines, and water-control devices which often has lethal results.
We also now know that manatees can not only hear sounds across a wide range of frequencies, from 90.5 kHz, (> 2 octaves higher than a human) to as low as 250 Hz, but also have the ability to determine sound directionality. These abilities may be help manatees use natural sounds to navigate, but also may put them at risk to boat strikes when the confusion of hundreds of boat motors are racing by in different directions and these sounds are reflecting in every direction possible.
If we are going to adequately protect manatees from natural and man-made threats, research with the animals in our care is vital. Knowledge gained can be directly applied to conservation management decisions and the development of technologies aimed at reducing human-induced manatee mortality.
Debborah Colbert, PhD