Kamis, 27 Oktober 2016

THE LIFE OF DUGONG



    Dugong is a medium sized marine mamal which belongs to the order Sirenia. It is the only living representative of the family Dugongidae. The word 'dugong' derives from the Tagalog, which was adopted from Malay, 'duyung', both mean "lady of the sea". In other countries they are also called as sea pig, sea camel, or sea cow. 
Kingdom:
Phylum:
Class:
Order:
Family:
Subfamily:
Dugonginae
Simpson, 1932
Genus:
Dugong
Lacépède, 1799
Species:
D. dugon
    The dugong has been hunted for thousands of years for its meat and oil. Traditional hunting still has great cultural significance in several countries in its modern range, particularly northern Australia and the Pacific Islands. The dugong's current distribution is fragmented, and many populations are believed to be close to extinction. The 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. Despite being legally protected in many countries, the main causes of population decline remain anthropogenic and include fishing-related fatalities, habitat degradation and hunting. With its long lifespan of 70 years or more, and slow rate of reproduction, the dugong is especially vulnerable to extinction.
     Dugongs are found in warm coastal waters from the western Pacific Ocean to the eastern coast of Africa, along an estimated 140,000 kilometres (86,992 mi) of coastline between 26° and 27° degrees to the north and south of the equator. Today populations of dugongs are found in the waters of 37 countries and territories. Recorded numbers of dugongs are generally believed to be lower than actual numbers, due to a lack of accurate surveys. Despite this, the dugong population is thought to be shrinking, with a worldwide decline of 20 per cent in the last 90 years. They have disappeared from the waters of Hong Kong, Mauritius, and Taiwan, as well as parts of Cambodia, Japan, the Philippines and Vietnam. It has been observed that shallow waters are used as sites for calving, minimising the risk of predation. Deep waters may provide a thermal refuge from cooler waters closer to the shore during winter.
        The dugong's body is large with a cylindrical shape that tapers at both ends. It has thick, smooth skin that is a pale cream colour at birth, but darkens dorsally and laterally to brownish-to-dark-grey with age. The colour of a dugong can change due to the growth of algae on the skin. The body is sparsely covered in short hair, a common feature among sirenians which may allow for tactile interpretation of their environment. These hairs are most developed around the mouth, which has a large horseshoe shaped upper lip forming a highly mobile muzzle. This muscular upper lip aids the dugong in foraging. The dugong's tail flukes and flippers are similar to those of dolphins. These flukes are raised up and down in long strokes to move the animal forward, and can be twisted to turn. The forelimbs are paddle-like flippers which aid in turning and slowing. The dugong lacks nails on its flippers, which are only 15% of a dugong's body length. The tail has deep notches.


         A dugong reaches sexual maturity between the ages of eight and eighteen, older than in most other mammals. The way that females know how a male has reached sexual maturity is by the eruption of tusks in the male since tusks erupt in males when testosterone levels reach a high enough level. The age when a female first gives birth is disputed, with some studies placing the age between ten and seventeen years, while others place it as early as six years. There is evidence that male dugongs lose fertility at older ages. Despite the longevity of the dugong, which may live for 50 years or more, females give birth only a few times during their life, and invest considerable parental care in their young. The time between births is unclear, with estimates ranging from 2.4 to 7 years.
      Mating behaviour varies between populations located in different areas. In some populations, males will establish a territory which females in heat will visit. In these areas a male will try to impress the females while defending the area from other males, a practice known as lekking. In other areas many males will attempt to mate with the same female, sometimes inflicting injuries to the female or each other. During this the female will have copulated with multiple males, who will have fought to mount her from below. This greatly increases the chances of conception.
     Females give birth after a 13–15 month gestation, usually to just one calf. Birth occurs in very shallow water, with occasions known where the mothers were almost on the shore. As soon as the young is born the mother pushes it to the surface to take a breath. Newborns are already 1.2 metres (4 ft) long and weigh around 30 kilograms (66 lb). Once born, they stay close to their mothers, possibly to make swimming easier. The calf nurses for 14–18 months, although it begins to eat seagrasses soon after birth. A calf will only leave its mother once it has matured.

          Dugongs, along with other sirenians, are referred to as "sea cows" because their diet consists mainly of sea-grass. When eating they ingest the whole plant, including the roots, although when this is impossible they will feed on just the leaves. A wide variety of seagrass has been found in dugong stomach contents, and evidence exists they will eat algae when seagrass is scarce. Although almost completely herbivorous, they will occasionally eat invertebrates such as jellyfish, sea squirts, and shellfish.
Hasil gambar untuk dugong




QUIZ
1.      Why is dugong vulnerable to extinction?
a.       Because it has been hunted for its oil and meat
b.      Because it has some rare disease
c.       Because it has long lifespan and slow rate of reproduction
d.      Because it needs a new habitat
e.       Because it has no food
2.      What is the family of dugong?
a.       dugongidae
b.      manatee
c.       sirenia
d.      animalia
e.       dugon
3.      why are the dugongs often referred as sea cows?
a.       because they look like cows
b.      because they eat sea grass
c.       because they have a relation with cows
d.      because they are in the same classification as cows
e.       because they are mammals
4.      Why are the dugongs being hunted?
a.       because of their oil and meat
b.      because of their tail
c.       because of their flipper
d.      because of their skin
e.       because of their paddle
5.      when does dugong reach its sexual maturity?
Dugong Marsa Alam.jpg
Hasil gambar untuk dugong anatomy
A dugong mother with a calf half its size travelling just above the seabed
a.       between the ages 8 to 18
b.      10 to 20
c.       1 to 5
d.      5 months to 5 years
e.       20 to 30
  































Kamis, 13 Oktober 2016

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