Friday, August 26, 2011

Dugong : Non-Violent Underwater Giants

Dugong : Non-Violent Underwater Giants-Kalpana Palkhiwala*

Marine mammals form a fascinating group of animals including whales, dolphins, seals and the dugong, also known as the sea cow. Being mammals, they are more closely related to elephants, leopards, bats and hares than they are to sharks and other fish. There are some 120 species of marine mammal to be found in the world, and a fourth of these may be found in India and adjacent countries.Dugongs are one of the ancient living creatures underwater and are most interesting aquatic mammals. Perfect non- violent underwater giant do not injure any living creature. Because of their grass-eating habit, they are known as sea cow. The size, average four meter-long, does not matter and this mammal surf on waters every 15 minutes like Gangetic Dolphins and whales, for breathing. Unlike whale and dolphins, dugongs release breathing sounds like musical notes, hence were named Sirenades. Also unlike seals, they never come up on the land. Nature has lost Sea-Cows to poachers.
Distribution     Dugong are large marine mammalian grazers of the tropical Indo-west-Pacific region. They are the only extant member of the family Dugongidae in the order Sirenaia. The range of the dugong extends over the coastal waters of some 37 countries ranging from east Africa, through south and south-east Asia to Australia. This herbivorous mammal, inhabiting the marine environment was once abundant in many parts of its range but numbers have declined and its area of occupancy has decreased in recent times due to exploitation and loss of habitat. Dugongs occur along some parts of Indian coast line and more commonly in west pacific. In Indian waters, the largest population exists between India and Sri Lanks in the Gulf of Mannar and in Palk Bay.  Abundant pastures of sea grass meadows grow in the shallows, providing food. They have been reported from the Gulf of Kutch, off the Saurashtra coast and in the Andaman and Nicobar Islands. Many young calves were sighted in the Gulf of Kutch during 1990, which indicates that this could be a reproductive zone.Dugongs swim in family groups consisting of a single young and its parents. Their attachment to each other is very strong which results in the capture of entire family.
Body    Like all modern sirenians, the dugong has a large and fusiform body with no dorsal fin or hind limbs. They are grey to brown in color. They have thick, smooth skin that is a pale cream color at birth but darkens dorsally and laterally to a brownish to dark gray with age. The body is sparsely covered in short hair, which allow for tactile interpretation of their environment.  They have a tail with flukes, like a whale, which provides locomotion through vertical movement and flippers. They do not have a dorsal fin like a shark. They have a wide flat nose, small eyes, and small ears. They possess paddle-like forelimbs without nails. The dugong is heavily dependent on seagrasses for subsistence and is thus restricted to the coastal habitats where they grow, with the largest dugong concentrations typically occurring in wide, shallow, protected areas such as bays, mangrove channels and the lee sides of large inshore islands. Dugongs reach an average adult length of 2.7 metres (8.9 ft) and 3 metres (9.8 ft) long and weigh as much as 400 kg (882 1b).Females tend to be larger than males. The largest known dugong was a female landed off the Saurashtra coast of west India, measuring 4.03 metres (13.2 ft) and weighing 1,018 kilograms (2,240 lb).
Food    Dugongs feed primarily on near-shore sea grasses. They are particular about their diets, with certain “fields” of sea-grass being regularly cropped. Dugongs are exclusively bottom feeders. Their primary feeding mechanism is uprooting sea-grass by digging furrow in the seafloor with their snouts. Reflecting this, the muscular snouts of dugongs are more dramatically tapered than those of manatees.They have a large body size and a hindgut fermenting digestive system. These features, combined with the relatively low nutrient and energy content of their aquatic plant food, suggest that they must spend a high proportion of their time feeding in order to meet their daily food requirements. Thus, they spend little of their time at or near the surface but must surface for 1 to 2 seconds to breathe at regular and frequent intervals.
Life Cycle  A dugong reaches its adult size between the ages of 9 and 18 years, longer than in most other mammals. Dugongs are humanly social, live in familial bonds, and surrender en masse if any of their family members be netted by a fisherman by chance. Dugongs bear one calf at a time after an approximately 13-month gestation.  It drinks milk from its mother until about two years old. Despite the longevity of the Dugong, which may live for fifty years or  up to seventy years, females give birth only a few times during their life and invest considerable parental care in their young.
Migration  The dugong is a migratory animal, but very slow moving. Instances have been recorded while many dugongs travelled less than 15 km (9 mi), some went as far as 560 km (348 mi). Scientists believe that dugongs move long distances for several reasons. They may be looking for food, as cyclones or floods can affect the seagrass. Males may be following females, or looking for their own territory. Dugong do not prefer cold water.If the water gets cold, less than 17 degrees Centigrade, they  travel to warmer areas.
Threat  The dugong has been hunted for thousands of years for its meat and oil, although dugong hunting also has great cultural significance throughout its range. The dugong’s current distribution is reduced and disjunct, and many populations are close to extinction.Dugong are hunted for throughout their wildlife range, usually for their meat and blubber. The seagrass beds which the dugong depend on for food are threatened by eutrophication caused by agricultural and industrial runoff, and dugong waste matter is a major food source for other aquatic creatures. Due to their shallow-water feeding habits, dugong are frequently injured or killed by collisions with motorized water vessels. Because of their large size, they have only a few predators. These include sharks, killer whales and saltwater crocodiles.       Thsudden escalation of the illegal activities is a big threat. The number captured or slaughtered has multiplied by 14 times or more within the past 2 years. The use of dynamite sticks is accelerating the possible depletion of this animal aided by other factors such as sail boat trawling along the shore line and the sea grass beds both day and night. The habitat perturbations due to excessive and unregulated mechanised fishing have also become a very critical factor not only disturbing the animals but in incidental capture as well as destroying their grazing grounds.
Status   The International Union for Conservation of Nature (IUCN) lists the dugong as a species vulnerable to extinction, while the Convention on International Trade in Endangered Species limits or bans the trade of derived products based on the population involved.It is currently listed in the IUCN Red List of Threatened Speices as being vulnerable to extinction throughout its global range (IUCN 2007). It is also listed in Appendix I of the Convention on International Trade in Endangered species of Wild Fauna and Floar (CITES), which prohibits all trades in this species or any products derived from it. In India, dugong has been given the highest level of legal protection and is listed under Schedule I of the India Wildlife Protection Act, 1972. Recognizing the threats to this marine mammal, the Government of India and the Ministry of Environment and Forests signed the CMS-UNEP MoU for the conservation and management of the dugong in April 2008.
Dugong Conservation in India
Three areas of the Indian coast have remnant populations of Dugongs: the Gulf of Kutch, the Gulf of Mannar and the Palk Bay, and the Andaman and Nicobar waters. However, these populations are threatened by mechanized fishing and illegal hunting, pollution and destruction of coral reefs and sea grass beds.In October 2010, a ‘Task Force for the Conservation of Dugongs’ was constituted, with the agenda to look into the entire range of issues related to their conservation, and towards the implementation of the UNEP/CMS Dugong Memorandum of Understanding in India.

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