The Dugong, a Huggable, Seagrass-Loving Sea Cow, Has a New Best Friend: Drones

To see a dugong is to want to hug a dugong, with its round body, gently curved flippers and gigantic smiling face. Along with their manatee cousins, these marine mammals have earned the nickname “sea cows” thanks to their grazing habits, consuming up to 85 pounds of seagrass a day.

Seagrass, in turn, depends on the sunlight that illuminates shallow coastal waters. In Australia, where a wide and well-lit continental shelf boasts plentiful seagrass, dugong populations can thrive. “Australia was probably always the dugong capital of the world,” says Helene Marsh, a leading dugong expert at James Cook University in Queensland, Australia.

East Africa has a similarly wide continental shelf and may once have housed as many dugongs as Australia, but coastal development and pollution have destroyed seagrass beds. Meanwhile, indiscriminate fishing tools such as gill nets ensnare and drown dugongs. At a reproductive rate of one baby every three or four years, dugongs are slow to recover from losses, and the East African population is now critically endangered.

The largest remaining group comprises about 300 dugongs living in the protected waters of Bazaruto Archipelago National Park in Mozambique. Smaller groups dot the coast from southern Somalia to Maputo Bay in southern Mozambique, but aircraft surveys are too expensive to regularly map these scattered populations. The last surveys to assess Maputo Bay, in the early 2000s, reported only one to four dugongs.

But recent technological advances bring opportunity. In 2020, Damboia Cossa, a Mozambican researcher at the University of Gothenburg, Sweden, used off-the-shelf aerial drones to look not for dugongs themselves but for the distinctive feeding trails they leave behind. Over six months, she made 12 drone flights at low tide, when Maputo Bay’s seagrass beds are easy to photograph.

To process thousands of pictures, Cossa trained a machine learning model to identify the feeding trails. In 2023, she was able to publish good news. “We saw really a lot of trails. They’re still coming to that place—still eating that seagrass.” There’s no reliable method yet to convert the number of feeding trails to the number of dugongs, but Cossa estimates that as many as 10 or even 20 dugongs now graze in Maputo Bay. Unfortunately, she found, their preferred seagrass meadows often bring them dangerously close to gill nets.

But the details of this overlap, she believes, can help inform wildlife management decisions about when and where to restrict fishing. Her plan now is to share her data with the local community, building awareness about dugongs and inviting fishers to participate in future surveys and figure out safer fishing practices. “Let’s try to save the few dugongs left.”