By Ranil Nanayakkara and Nilantha Vishvanath
Bio-Diversity Education and Research (BEAR)
The Dugong (Dugong dugon) is the only herbivorous mammal that is strictly marine and is the only surviving species in the family Dugongidae; there are two subspecies which are presently recognized - Dugong dugon dugon of the Indo-Australian region and Dugong dugon hemprichii of the Red Sea. The other members of the order Sirenia, the three species of manatee include the Amazonian manatee, the West African manatee and the West Indian manatee of which there are two subspecies; the Antillean manatee and the Florida manatee.All species of manatee inhabit fresh water to varying degrees at different times. The only other recent Sirenia is the giant Steller’s sea cow, who grows to almost ten meters in length, but sadly was hunted to extinction just twenty seven years after its discovery in the 18th Century. All surviving species of the order Sirenia are listed as vulnerable to extinction. This zoological order was named "Sirenia" as these creatures were equated to the legendary mermaids of the olden day sailors.
‘Sirenias, in Greek mythology, were sea-nymphs, who by their singing, fascinated and later destroyed those who approached their locality. The female dugong is proverbial among the Malays for her maternal solicitude for her offspring, and this is supposed to be one of the sources of the mermaid legend. Near at hand, these creatures would never be mistaken for human beings, "but seen at a distance, by fearful and wondering voyages along the coast, such an error might easily happen, for they frequently stand upright among the weedy shallows of the coasts, perhaps draped with loosened vegetation like long hair, and holding to their breasts a young one who nurses from pectoral mammae such as a human baby would do" (Ingersoll, 1938).
In 1493, Christopher Columbus, observing manatees off the coast of Hispaniola, noted that ‘although these mermaids had something like a human face, they were not quite as handsome as they had been painted’.’
The dugong historically had a wide range, that spanned at least 37 countries and geographical territories and including tropical and subtropical coastal waters, specially around islands where shallow waters promote the growth of "sea grass" from east Africa to Vanuatu. Though once widely distributed, it is now restricted to coastal waters of parts of the Indian and Pacific Oceans, largely due to being overhunted for meat and especially oil. The dugong’s historic distribution is believed to have been broadly coincident with the tropical Indo-Pacific distribution of its food plants, namely the Phanerogamous plants of the families Potamogetonaceae and Hydrocharitaceae, more commonly known as "sea grass". The largest surviving populations are found in Northern Australian waters and the second largest in the Arabian Gulf.
The dugong is an obligate bottom feeder (grazer); it eats vascular sea grasses that are comparable to terrestrial grasses; the roots being the most nutritious. It may feed on brown algae in times of critical food shortage, but studies have shown that algal material is not readily digested. Ongoing research in Sri Lanka has shown that the dugongs in Sri Lankan waters are partial to certain species of sea grasses like Halophila spp. and Halodula spp. which are supposed to be high in nutrients.
Dugong being a specialist herbivour, its distribution within its existing range is mainly confined to sea grass beds, which occur in calm and shallow coastal areas, such as bays and lagoons; as such the only records in Sri Lanka, come from the North Western province i.e.Puttalam lagoon, Kalpitiya, Mannar, Jaffna and sporadically in Trincomalee and Batticaloa according to available records. They have also been observed in waters farther offshore in areas where the continental shelf is wide, shallow and protected.
Dugongs have often been reported from the Palk Strait and the Gulf of Mannar. The latter encompasses a group of 21 islands and 81 slightly elevated pearl banks with sea grass communities dominated by Halophila Spp; based on the composition of the sea grass communities and their bathymetry, Palk Strait and the Gulf of Mannar are important areas as dugongs habitats. The precise status of the dugong in this region is yet to be established, but however it is generally acknowledges that the population has drastically depleted in recent years. Anecdotal reports state that "it is rare nowadays for more than one specimen to be taken, whereas formerly in the Gulf of Mannar they were found in their myriads, numbers running in to their hundreds".
A commercial dugong fishery existed in Sri Lanka in the past, when these mammals were abundant. In the 1950’s; 100–150 animals were killed annually in the Mannar district. Excessive, uncontrolled harvesting for their meat, hide and oil have made the Dugongs rare in Sri Lankan waters at present. Recent surveys show that the remaining populations of dugongs in our waters are confined mainly to the Gulf of Mannar.
However, the dugong being a proclaimed protected species in Sri Lanka under the Fauna and Flora Protection Ordinance enjoys very little actual protection in its fragile & localized habitat.
During recent surveys carried out in the North Western province, fisher folk as well as the villagers inhabiting the coastal areas, when asked if they have seen dugongs, responded that they hardly see any, but on isolated occasions solitary animals are encountered, that too, rarely in pairs. When questioned if they are killed, they admitted to doing so for the reason that it is financially rewarding and easily sold. We came across carcasses and remains of five different individuals of dugong in the Silavathurai, Kalpitiya and Mannar areas. Furthermore the survey revealed that a kilogram of meat draws around LKR 800-1,500. When questioned as to why pay such a high price, the reply from a villager was "the meat is considered highly palatable and nutritious."
Dugongs are one of the most endangered large mammals of Sri Lanka, if not the world. They are vulnerable to adverse human activity in their habitats due their life history and their dependence on sea grasses that are restricted to coastal habitats. These areas are often under pressure from human activities such as direct human exploitation, habitat degradation and destruction, also incidental capture during fishing operations in the North Western coast. These pressures have resulted in drastic reduction of their population. If stringent measures are not taken urgently and immediately to protect this leviathan, it will very shortly vanish forever from this "Resplendent Isle" it maybe already too late, but yet we can try…
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