Much as the sirens of Greek mythology were said to mesmerize sailors, the family of gentle sea creatures known as Sirenia—manatees and dugongs—captivated photographer Jason Gulley as he spent months documenting Florida manatees for the story in the January issue of National Geographic.
Unlike the much-loved manatee in the Sunshine State, little is known about the two other species and the dugong, a cousin found in coastal waters from East Africa to Australia. The International Union for Conservation of Species lists all four as vulnerable, in part because of hunting and degradation of their waters.
“What we know about Florida manatees is thanks to the fact that they congregate in water that is clear enough for us to see them,” says Gulley, who’s a National Geographic Explorer. “Amazonian manatees, by contrast, are nearly impossible to see, much less to photograph. The locals call them ghosts.”
Now, for the first time, a research team using sonar technology has “seen” these elusive animals in the wild, in a protected area in Brazil.
Amazonian manatees—the smallest, at eight to nine feet long and weighing between 650 and a thousand pounds—are the only ones that live entirely in fresh water, in rivers darkened by sediment washed down from the Andes and stained reddish-brown by decomposing forest vegetation. The murky, tannic waters explain why researchers rarely if ever see the animals.
“Studying them is very challenging—you have to build up from little scratches, working on signs, vestiges, remains, bones,” says Miriam Marmontel, a member of the National Geographic team and a leading expert on Amazonian manatees at Mamirauá Sustainable Development Institute, in Tefé, Brazil.
“While other creatures like otters and river dolphins are more visible, manatees are different,” she says. “You just never see them.” Throughout a career spanning several decades, Marmontel says she’s averaged just one glimpse a year.
Enter multibeam sonar
Marmontel’s frustration is diminishing. She’s part of a small team of researchers funded by the National Geographic Society who are pioneering use of imaging technology called multibeam sonar to document the lives of Amazonian manatees. Because no one knows how many manatees live in the sprawling Amazon Basin, one hoped-for outcome is a population estimate—crucial for developing strategies to protect the animals, Marmontel says.
“The question about abundance has been on our minds forever,” she says. “Everyone asks about it, and we just don’t know.”
Originally developed by the U.S. Navy in the 1960s to create scans of the seafloor and detect objects in the water column, multibeam sonar works by sending out multiple sonar beams in a fan-shaped pattern and measuring the time it takes for sound waves to reflect off the seabed or other objects back to a receiver. The result: detailed images that offer unprecedented ability to study manatees in dark waters.
National Geographic Explorer Daniel Gonzalez-Socoloske, of Andrews University, in Michigan, saw how multibeam sonar had helped researchers monitor seal behavior around tidal power turbines in Scotland, so he teamed up with Gulley and Marmontel to find out if it could reveal the hidden world of Amazonian manatees. (Read how Florida's beloved manatees are dying in alarming numbers again).
First, they tested the equipment at CREA, a rehabilitation facility for sick or injured manatees in Iquitos, Perú. The results were promising: The sonar produced clear visuals of manatees, making it possible to observe and record what they were doing in real time.
So the team set out to Mamirauá Sustainable Development Reserve, a 4,300-square- mile protected swath of flooded forests and wetlands in the remote, western heart of the Amazon near Tefé. Working from a floating field research base, they spent weeks collecting sonar visuals of wild manatees traversing a narrow channel during their annual migration from flooded forests to shelter during the dry season in oxbow lakes, formed when bends in a river are cut off from the main channel.
It’s exciting to watch the sonar “videos”—the first-ever documentation of Amazonian manatees in their natural habitat, Gonzalez-Socoloske says. “These are not animals bumbling around bumping into things—they’re curious creatures, they have personalities, they can move gracefully through a very complex environment without touching anything.”
“It’s literally opening up a whole new field of study, like when the microscope was invented—there’s a whole micro-universe there that we assumed existed, but that we’d never seen.” By micro-universe, he means a world beyond that detectable by the naked human eye. The sonar images reveal much to the scientists, but for non-experts, they aren't as illuminating.
Tapping local knowledge
Marmontel says the effort would have been impossible without the help of members of local communities. “The only people who have any kind of knowledge about Amazonian manatees are the people that hunt them,” she says. “They understand the movement and habits of manatees better than any researcher. “They would tell us, ‘Here’s one coming!’ We’d watch the sonar screen and say, Oh! Yes! There it is.”
During the 1930s and 1940s, commercial hunters along tributaries of the Amazon killed thousands of manatees for their skins, used to make water hoses and machine belts. Cheaper synthetic alternatives ended the slaughter by the mid-20th century. Killing manatees throughout the Amazon has been illegal since the 1960s, but hunting still occurs, Marmontel says. It’s a tradition among some families who have honed their understanding of the animals and their movements over centuries.
Gonzalez-Socoloske says he accepts collaborating with hunters for the greater good of the animals they study. “My personal philosophy is that I’m willing to work with anyone—if we have anything in common, I’m willing to work with that. There are too few allies.”
He continues: “Manatee hunters have a high regard and respect for the natural world.” But the tradition is dying out. “Younger people don’t have the patience for the hunt—hunting manatees requires a keen sense of behavior, of knowing where they’ll surface.”
Marmontel believes multibeam sonar can revolutionize our understanding of these secretive animals, but, she says, there’s much to learn before viable population estimates can be calculated. A sonar image, unlike a photo, is more like an x-ray or ultrasound picture. It takes skill and experience to interpret the images.
The researchers hope to assemble a catalog of sonar images that can be cross-checked with ones obtained with side-scan sonar, which gives less detailed views but also is less costly to use. Eventually, with a large enough image database, they’ll be able to create algorithms that reliably detect manatees round the clock with side-scan sonar equipment positioned in channels widely throughout the Amazonian Basin.
Among historians of philosophy and science, the principle “as above, so below” is often understood in reference to the effects of celestial movements on terrestrial events.
In the distant cosmos above Earth, a manatee lurks. Visible only through radio waves, the “manatee nebula” was formed by the violent death of a star in a supernova explosion some 30,000 years ago. At its core, an unusual black hole emits powerful jets of particles that are accelerated in the manatee’s “head.” While this galactic sea cow may hold clues to understanding astrophysical phenomena, its earthly Amazonian counterpart may hold secrets to understanding the nature of tropical rivers.
As if mirroring each other, both manatees reflect our urge to know more. By combining new technology with traditional knowledge, the researchers in the Amazon are beginning to plumb Marmontel’s “magical” creatures.
“I think they’re an important piece of the ecosystem,” she says. “We just don’t know why.”