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Dugong
 
   
   

Order : SIRENIA
Family : Dugongidae
Species : Dugong dugon

Head-body length : Typically up to 3.0 metres
Weight : Typically up to 400 kg
(with some examples far exceeding this weight)

The Dugong is the only representative of the order Sirenia (the 'sea cows') to occur in the warm, tropical waters of Southeast Asia. The species is related to the three species of manatee, which occur in west Africa, the Caribbean and the Amazon.

In terms of evolution, Dugong and manatees appear to be more closely related to elephants than they are to other marine mammals such as whales and dolphins. IUCN classifies the Dugong as 'vulnerable'.

A closely-related species, the huge Steller's Sea Cow Hydrodamalis gigas, from the Russian Far East, was sadly hunted to extinction in the 18th century.

Dugongs inhabit warm, shallow, tropical and sub-tropical coastal waters which support the growth of seagrass, their main source of food.

Seagrasses are a diverse group of around 60 species of angiosperm (flowering plants) whose roots anchor themselves in soft, marine sediments (most seagrasses, however, spread through the growth of rhizomes hidden in the substrate). Many species have long, grass-like, narrow leaves but many others bear small, rounded leaves. Rhizomes, roots and leaves are all consumed by dugongs.

Dugongs are known to swim many kilometres from one feeding area to another but, reportedly, they can only remain submerged for just 6 minutes: this leaves them at risk of being injured or killed by ship propellers.

Adults typically weigh up to 400 kg, however there have been numerous examples much larger than this. Their distinctive features includes a downward-facing mouth, a broad snout with thick bristles, a pair of valved nostrils, small eyes, two small tusks (upper incisors) in males, front limbs in the shape of flippers, an absence of hind limbs, a dorso-ventrally flattened tail fluke and thick skin with large amounts of blubber.

Females usually give birth to a single calf, and the young are dependent upon the mother for at least 2 years.

Dugongs range widely in the Indian Ocean, from the Red Sea and the east coast of Africa to the coastlines of India, Myanmar, Thailand, Peninsular Malaysia, Indonesia and Western Australia. Further east they inhabit the thousands of islands of Indonesia and the Philippines, the South China Sea (including Cambodia and Vietnam) and the western Pacific Ocean (Papua New Guinea, Solomon Islands, eastern Australia etc.).

Dugongs still maintain a foothold in shallow waters around Singapore, as evidenced by rare sightings and by the presence of feeding trails in seagrass beds (Figure 3).


Fig 1 : Adult dugong swimming in a clear, tropical sea.

Fig 2 : Example from the shallow waters of the Red Sea, actively feeding on seagrass. Note the closed valves at the entrance to the nostrils.

Fig 3 : A fresh dugong feeding trail in seagrass is revealed at low tide at Changi Beach, Singapore, just a stone's throw from one of the world's busiest airports.  Photo thanks to Ria Tan.

Fig 4 : Short, ribbon-like seagrass from Sulawesi, Indonesia.


References : M5


Links :

Wild Singapore
Wild Shores of Singapore


Image attribution :
Fig 1 by Geoff Spiby and Fig 2 by Julien Willem are licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.

Fig 3
photo courtesy Wild Singapore (Ria Tan).
 

Fig 1
  
ゥ Geoff Spiby 
Fig 2
  
ゥ Julien Willem
Fig 3
  
ゥ Wild Singapore / Ria Tan

Fig 4