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.
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Phylum:
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Class:
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Order:
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Family:
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Dugongidae
Gray, 1821 |
Subfamily:
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Genus:
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Species:
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D. dugon
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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.
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?
b.
10 to 20
c.
1 to 5
d.
5 months to 5 years
e.
20 to 30
