‘Gentle Giants:’ The Secret Life of the Antillean Manatee
By LIDA TUNESI
Seeing one of Florida’s “gentle giants” – the manatee – can be a trip highlight for travelers to the Sunshine State. But the Florida manatee has a lesser-known cousin that lives along coastlines in the Caribbean and parts of Central and South America. The Antillean manatee, considered endangered by the International Union for Conservation of Nature, has been studied much less than its Florida relatives.
Ph.D. candidate Eric Ramos (Hunter College, The Graduate Center) was a co-author on two studies that will help researchers make headway into learning more about the Antillean subspecies. One paper, published in Endangered Species Research, could improve manatee monitoring and thus contribute to conservation efforts. The other, which appears in Journal of the Acoustical Society of America, is a step toward better understanding how Antillean manatees communicate.
“The Antillean manatee lives in a lot of places where they haven’t been well-studied,” said Ramos. “It’s exciting to learn new things about species that are sometimes thought of as simple when they are anything but. These animals are also endangered, with a small remaining population and a high rate of deaths from vessel collision.”
Knowing more about the manatees’ survival and reproduction rates and their movement habits would be a boon to conservation efforts, but monitoring animals that live in remote, marine habitats is hard. Observing the manatees from boats, which can injure the animals, isn’t necessarily the best option.
Instead, Ramos and colleagues proposed and tested using drones. The team used small commercial drones to capture images of the animals around lagoons and seagrass flats in Belize. At low altitudes, they found, the resolution was good enough to identify individual manatees by scars or other markings. Though the method works, the authors advised that future studies should take care to choose flight speeds and angles that don’t disturb the animals.
In the other study, Ramos and Professor Diana Reiss (Hunter College, The Graduate Center) investigated the Antillean manatees’ vocal behavior. Researchers know that manatees make different types of sounds, such as “trills” and “squeaks,” and that the sounds serve purposes such as letting a mother manatee stay in touch with her child. But most studies on manatee vocals have focused on the Florida subspecies.
The scientists brought a recorder to Belize, where they anchored it underwater in a seagrass channel to eavesdrop on the manatees. The recordings showed broadband vocalizations, a large number of which were partly composed of ultrasonic frequencies – noises too high for humans to hear. At this point the researchers can only guess at the significance of such high sounds – maybe ultrasonic frequencies help manatees stay in contact in noisy places. Such questions are good motivation to do longer recordings, possibly months-long, to figure out what these ultrasonic frequencies are for and how they evolved.