The Dugong Dugong Dugon Is A Large Marine Mammal Which Essay Example

throughout their range, the main causes of population decline remain anthropogenic, and include hunting, habitat degradation, and fishing-related fatalities. 8] With its long lifespan and slow rate of reproduction, the dugong is especially vulnerable to these types of exploitation. [3] In addition, dugongs are threatened by storms, parasites, and their natural predators, sharks, killer whales, and crocodiles. [8] These enormous vegetarians can be found in warm coastal waters from East Africa to Australia, including the Red Sea, Indian Ocean, and Pacific.

Dugongs are related to manatees and are similar in appearance and behavior— though the dugong's tail is fluked like a whale's. Both are related to the elephant, although the giant land animal is not at all similar in appearance or behavior.Dugongs graze on underwater grasses day and night, rooting for them with their bristled, sensitive snouts and chomping them with their rough lips. These mammals can stay underwater for six minutes before surfacing. They sometimes breathe by "standing" on their tail with their heads above water. Dugongs spend much of their time alone or in pairs, though they are sometimes seen gathered in large herds of a hundred animals.

Female dugongs have one calf after a yearlong pregnancy, and the mother helps her young reach the surface and take its first breath.A young dugong remains close to its mother for about 18 months, sometimes catching a ride on her broad back. These languid animals make an easy target for coastal hunters, and they were long sought for their meat, oil, skin, bones, and teeth. Dugongs are now legally protected throughout their range, but their populations are still in a tenuous state.

Some believe that dugongs were the

inspiration for ancient seafaring tales of mermaids and sirens. Type: Mammal Diet: Herbivore Average lifespan in the wild: 70 years Size: 8 to 10 ft (2. 4 to 3 m) Weight: 510 to 1,100 lbs (231 to 499 kg)Group name: Herd Protection status: Threatened Size relative to a 6ft (2m) man: Geographic Range Found discontinuously in coastal waters of east Africa from the Red Sea to northernmost South, northeastern Indian, along the Malay peninsula, around the northern coast of Australia to New Guinea and many of the island groups of the South Pacific. Range was greater in the past. Habitat Dugongs inhabit shallow, tropical marine coastal water and are more strictly marine than manatees. Physical Description Birth Mass 27500 g (average) [Ref] (968 oz) Mass 230 to 908 kg (506 to 1997.

lbs) Dugongs are born a pale cream color, but they darken with age to a deep slate gray dorsally and laterally. The short hair is sparsely distributed over the body, save the bristles on the muzzle. The skin is thick, tough and smooth. The front-limbs have evolved into flippers that are 35-45 cm long. These are used for propulsion by young, but the adults use the fluke-like tail for locomotion, using the flippers for steering. Despite its diet, the dugong ha s a relatively simple stomach.

The muscular upper lip is cleft and protrudes over the down turned mouth.The lower lip and distal parts of the palate have horny pads used to grasp vegetation, which is then uprooted with the strong upper lip. The dental formula is 0/0 0/0 0/0 2-3/2-3, for a total of 10-14 teeth in adults. The molars are rootless, circular in

cross-section and lack enamel.

The premaxilla is enlarged and downturned, the nasal bones are absent, the braincase is small and the zygomatic arch is thick and deep. The bones of the skeleton are pachyostotic, which is to say extremely thickened and dense. Adults range in length from 2. 4 to 4 m.

Sexual dimorphism is either absent or females may slightly outsize males. Reproduction Gestation period 374 days (average) [Ref] Age at sexual or reproductive maturity (female) 3470 days (average) [Ref] Age at sexual or reproductive maturity (male) 3470 days (average) [Ref] Breeding occurs throughout the year and peak months for birth vary geographically. The exact length of gestation is unknown, but it is presumed to be about 1 year. Single calves are the norm and twins are rare. Parturition takes place in shallow water, and newborn calves are able to swim immediately to the surface for their first breath of air.

Newborn calves are about 100-120 cm long and weigh 20-35 kg. Newborns cling to the mother's back and ride from the surface to grass beds along with the feeding mother. Young suckle underwater beneath the mother in an inverted position. Lactation lasts approximately 18 months, but young are known to eat grass at 3 months.

Young may remain with the mother for a year. Sexual maturity is reached in both sexes by an age of 9-10 years, though it can occur as late as 15 years. Behavior Feeding is the principal activity of dugongs and typically occurs in water 1-5 m deep.Wear on the tusks and trails through grass beds suggest that some digging or rooting is part of the feeding behavior. Calluses on the flippers are

caused by "walking" on them or drifting across the bottom while feeding. Head shaking during feeding appears to be used to clean sediment from the food before ingesting as little sediment is reported in the stomach contents of animals examined.

The timing of feeding seems to be most closely related to tides, not photoperiod. Frightened animals make a whistling sound and calves have a bleat-like cry.Though now rare, herds of several hundred animals were formerly known. Calves formerly left the herd during the day to form nurseries in shallow water. Groups of 6 animals are most common now. Males are not known to stay with the stable mother-calf social units.

Long distance migration is unknown, but some daily and seasonal movements do occur in some populations. Tides, water temperature and food abundance are probably the main factors involved in these movements. Average swiming speed is 10 km/hr, but this can be doubled in a pinch. Dives typically last 1-3 minutes.Food Habits Dugongs are aquatic herbivores and feed on the phangerogamous sea grasses of the families Potomogetonaceae and Hydrocharitaceae.

Also reported to occasionally eat algae, and crabs have been found in the stomachs of dugongs. Economic Importance for Humans: Positive Dugongs are hunted throughout their range for meat,which has been likened to veal. They are also hunted for oil, hides for leather, and for their bones and teeth, which are made into ivory artifacts and charcoal for sugar refining. Some Asian cultures prize dugong products for medicinal purposes.

Conservation Status Dugongs are listed as endangered under the Endangered Species Act of the U. S. A. and as vulnerable by the IUCN. All populations are in CITES Appendix I except the

Australian populations, which are in Appendix II.

Other Comments Dugongs have a good fossil record going back to Eocene terrestrial ancestors. References Husar, S. L. 1978.

Dugong dugon. Mammalian Species Account No. 88. American Society of Mammalogists, 7 pp. Nowak, R.

M. 1991. Walker's Mammals of the World. The Johns Hopkins University Press, Baltimore.