Gentle giants of the sea
Grazing seagrass meadows within the tropical and subtropical coastal waters from East Africa to Vanuatu, and as far north as the southwestern islands of Japan, the charismatic dugong is becoming less and less common. In China, they recently were announced extinct, with no sightings recorded since 2008.
Most people would agree that dugongs are some of the most charismatic and interesting marine mammals out there. While often mistaken for manatees, dugongs don’t enter freshwater areas like their close relatives and many other factors make them stand out from other species. For instance, male dugongs grow tusks when they reach maturity. While females also tend to grow tusks, these erupt in older individuals. Dugongs breathe in oxygen at the surface through their nostrils, before they dive down to feed, holding their breath for up to 11 minutes doing so. Their eyesight might not be the best, but they can hear very well. Individuals communicate between each other using barks, squeaks, and chirps that can travel through water.
As the world’s only strictly herbivorous marine mammal, dugongs are reliant on seagrass meadows for food. However, as seagrass habitats continue to disappear all around the globe through the expansion of ports, dredging, and other factors, the survival of dugongs is also threatened. It is estimated that dugong populations have declined by 90% in the past 30 years.
Listed on the IUCN Red List of Threatened Species as ‘Vulnerable’ and commonly regarded as a globally threatened species, dugongs are increasingly threatened by human activities such as entanglement in fishing gear, pollution, boat collisions, poor water quality and human-caused loss of their primary food source – seagrass. While still thriving in some areas of the world, including Western Australia’s Kimberley, Pilbara and Shark Bay regions which are home to some of the largest remaining dugong populations in the world, human-induced pressures seemed to have been too much to bear for some local populations.
Sadly, new research led by the Zoological Society of London and the Chinese Academy of Sciences shows that the dugong – also known as the ‘sea cow’ – is functionally extinct in China, with no sightings recorded since 2008. According to the research, records of dugongs in Chinese waters have decreased rapidly from the 1970s onwards. With no records or evidence of their presence at all in China since 2008, this seems to be the first functional extinction of a large mammal in China’s coastal waters.
The new study, published in Royal Society Open Science, was undertaken by a team of international conservation scientists who conducted extensive interview surveys in local fishing communities across four southern maritime provinces in China. To build further evidence of potential dugong presence in those areas, they also reviewed historical data covering past dugong distribution in China.
Even though the species has been classified as a Grade 1 National Key Protected Animal since 1988 by the Chinese State Council – placing them under the highest protection afforded in the country – the pressures seemed too much for the species in China. Dugongs had been known to frequent southern Chinese waters for many hundreds of years, and the new surveys were undertaken in 66 fishing communities across four Chinese provinces along the coastal region of the South China Sea (Hainan, Guangxi, Guangdong, Fujian) to gather local knowledge about dugong sightings. The authors say that they would ‘welcome any possible future evidence’ that dugongs might still persist in China. However, this exhaustive survey found no recent evidence of dugong survival across their known distribution in mainland Chinese waters. The study authors now recommend that the species’ regional status should be reassessed as Critically Endangered (Possibly Extinct).
“In 2007, we tragically documented the likely extinction of China’s unique Yangtze River dolphin. Our new study shows strong evidence of the regional loss of another charismatic aquatic mammal species in China – sadly, once again driven by unsustainable human activity,” explained Professor Samuel Turvey of ZSL’s Institute of Zoology and co-author of the study. “The likely disappearance of the dugong in China is a devastating loss. Their absence will not only have a knock-on effect on ecosystem function, but also serves as a wake-up call – a sobering reminder that extinctions can occur before effective conservation actions are developed.”
Previously, scientists have discovered that dugongs, together with sea turtles, play an important role in seagrass ecosystems. On the one hand, their intensive grazing seems to alter the species composition of seagrass meadows which, in turn, favours rapidly growing species and makes seagrass meadows grow quicker. On the other hand, by eating and pooping out seagrass seeds, dugongs help spread these seeds over the ocean floor over large distances of up to 650km.
Dugongs are dependent on sea grass, and vice versa. But seagrass meadows are marine habitats that are being rapidly degraded by human impacts. Although seagrass restoration and recovery efforts are a key conservation priority in China and other parts of the world, restoration takes time that dugongs may no longer have.
Additional photographs by Ocean Image Bank – Anett Szaszi, Fabrice Dudenhofer, Jordan Robins, and Umeed Mistry.
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