Earth Protect Blog

By Mike Ives

© The New York Times Co.

The dugong, a species of socalled sea cow that roams the ocean floor in Asia and Africa and is said to have inspired ancient legends of mermaids, has been spotted off China’s southern coast for centuries.

But not lately. A new study suggests the dugong has become the first large vertebrate to go functionally extinct in China’s coastal waters, the result of a rapid population collapse there that began in the mid-1970s.

“Functional extinction” means that even if some dugongs are still alive off China’s coast, their numbers are too small to maintain a viable population. Dugongs are occasionally entangled in fishing nets, and the seagrass that they eat in the South China Sea’s northern reaches has degraded over the years.

The study in the journal Royal Society Open Science, based on interviews with nearly 800 fishermen in southern China and published online this month, is a cautionary tale for other mammals in the South China Sea — a site of stunning marine biodiversity that faces heavy pressure from overfishing, coastal development and other stresses.

There are still approximately 100,000 dugongs living in the waters off around 40 countries, but the latest findings do not bode well for populations of the animal in Japan and Southeast Asia, said Helene Marsh, an emeritus professor of environmental science at James Cook University in Queensland, Australia.

“It’s a sad story and a salutary story,” Marsh, who has studied the dugong for decades, said by phone Friday. “I don’t think it’s going to be the last place where people can conclude that dugongs are functionally extinct.”

Marine mammals, including dugongs, first evolved in the Eocene Epoch, around 54 million to 34 million years ago, particularly in the extensive shallow sea stretching from the Pacific to the present-day Mediterranean, according to research by Annalisa Berta, a professor emerita of biology at San Diego State University.

Dugongs belong to the Sirenia, a biological order that includes the three extant species of manatees. All four are known colloquially as “sea cows,” but the dugong is the only one that lives exclusively in salt water. It is also the world’s only fully vegetarian marine mammal.

Over the centuries, sirenians have inspired tales of mermaids and other mystical creatures. Marsh said many of the legends are based around the idea that sirenians, like the sirens of Homer’s “Odyssey,” lure sailors with magical properties. (The shallow, prehistoric body of water where dugongs developed, the Tethys Sea, was named after a sea goddess from Greek mythology.)

Dugongs once had an even larger range that stretched to the Western Atlantic and Caribbean, and there used to be several dugong species. One of them, Steller’s sea cow, was a source of food for 18th century hunters and explorers in the North Pacific, but it was declared extinct 27 years after its discovery in 1768.

Australia has the world’s largest population of dugongs today, thanks to an enormous, sparsely populated coast ringed with abundant seagrass, Marsh said. The population off southern China was never robust because there wasn’t as much seagrass there in the first place, she said.

Now the dugong may be gone from China’s coast forever, joining the Yangtze River dolphin and other species that have disappeared. The recent study described the rapid collapse of China’s dugong population since 1975 as a “sobering reminder that local extinction can happen within a very short time.”

The study, by researchers at institutions in China, Greece and Britain, is based on interviews conducted in summer 2019 with 788 fishermen along the southern China coastline. Only three reported dugong sightings occurred over the preceding five years.