I wrote the following species profile as part of my Marine Megafauna course, and got top marks through peer review! Thought I’d share it here for anyone interested in knowing more about dugongs.
Top photo © Jürgen Freund, Indo-Pacific Ocean
Dugong (Dugong dugon)
- Dugongs are often referred to as “sea cows”, as they graze on underwater meadows of seagrass. They are the only marine herbivorous mammal, as all species of manatee rely on freshwater to some extent
- Dugongs can spend up to six minutes underwater before needing to surface to draw breath
- There is a theory that the tales of sea sirens or mermaids originated from sightings of dugongs by seafarers
The dugong (Dugong dugon) is a marine mammal in the order Sirenia. The family Dugongidae consists of only four species still alive today. The word “dugong” translates as “lady of the sea” in both the Tagalog and Malay dialect, from which the term was originally derived. Dugongs are also referred to as Sea Cows, Sea Pigs and Sea Camels, but are not related to any of these animals. Dugongs are most closely related to the Stellar’s Sea Cow, which, in the 18th century, was hunted to extinction by humans. Their closest living relative is the manatee, which they resemble, with the key difference being the shape of their tails. While the tail of a manatee is round and spade-like, dugongs have tails that are fluked. Both species are actually related to a giant land animal – the elephant – although the behaviour and appearance of elephants and dugongs has diverged dramatically.
Dugongs range in length from 2.4 to 3.5 m, with a weight spanning the 231 – 499 kg range. Their coloration varies; juveniles are a pale cream colour that darkens with age both laterally and dorsally, and adults can be anywhere from a brownish to a dark grey hue. Other factors that affect the colour of the skin include the growth of algae, which can give off a greenish tinge. These large herbivores can be found in warm coastal waters from East Africa to Australia, and span the Red Sea, Indian and Pacific oceans. The preferred habitat of the dugong is shallow tropical and subtropical coastal and island waters. There are estimated to be around 85,000 dugongs in the world, with the largest population found in the waters of northern Australia, from Shark Bay (Western Australia) to Moreton Bay (Queensland).
In the wild, dugongs can live up to 70 years, but have a slow rate of reproduction. Sexual maturity in dugongs does not occur until after 10 years of age, and can take some females until they are 17 years old. One calf is produced after a gestation that lasts around 13-14 months, whereupon the mother will assist the newborn with reaching the surface to take its first breath.
Photo by Rutger Geerling on Flickr
Dugongs are vegetarians whose entire diet is made up of different species of seagrass. Studies have shown that dugongs prefer grasses that are delicate and higher in nitrogen, such as seawrack (Halophila ovalis) and narrowleaf seagrass (Halodule uninervis). They forage throughout the day and night, uprooting whole plants using their snouts. Because of this behaviour, dugongs create distinctive trails where they have fed. They have also been shown to manipulate the seagrass beds when feeding to facilitate plant growth, a behaviour called “cultivation grazing.”
Dugongs have been long sought after for their flesh, oil, bones, skin and teeth. As they are languid and slow-moving animals, and congregate in coastal regions and around islands, they make easy targets for hunters. Due to loss and degradation of habitat, impacts of fishing, hunting and coastal pollution, the total number of dugongs seems to be in decline, with the populations becoming increasingly fragmented. To counteract this trend, dugongs have become legally protected throughout their range, with further conservation efforts being centred on protecting dugong habitat through the creation of Marine Parks. Currently, the conservation status of dugongs is listed variously as endangered, threatened, and vulnerable to extinction.
Photo by Andrew Rankin
Dugong Expert: Professor Helene Marsh
Professor Helene Marsh’s research has centred around the population ecology and management of dugongs. Her research has formed the scientific basis for major marine conservation efforts, such as the establishment of Dugong Sanctuary in the Torres Strait. Helene is the current Dean of Graduate Research Studies and Professor of Environmental Science at James Cook University, and a program leader in the Marine and Tropical Science Research Facility.
Department of the Environment (July 2013) Dugong dugon in Species Profile and Threats Database, Department of the Environment, Canberra. Available here
Kelly N, Peel D (November 2013) Unmanned Aerial Vehicles (UAVs) for Surveying Marine Fauna: A Dugong Case Study. Available here
D’Souza E, Patankar V, Arthur R, Alcoverro T, & Kelkar N (October 2013) Long-Term Occupancy Trends in a Data-Poor Dugong Population in the Andaman and Nicobar Archipelago. Available here