Erzsebet Frey

Synonyms: australis, cetacea, dugung, hemprichii, indicus, lottum,
tabernaculi.

Chromosome number: 2n = 50.

Measurements; 2.4 (2.2--3.31) m; n = 18 WT: 250--570 kg

## Description {#description .wp-block-heading}

Rotund cetacean-like body with flippers and flukes that resemble those
of a dolphin without a dorsal fin.

Head resembles that of a walrus without the long tusks. Head
distinctive, with mouth opening ventrally beneath the broad, flat
muzzle. Eyes located on side of head, small and not prominent.
Externally, ears consist of small openings on either side of the head.

Adults grey in colour, but may appear brown from the air or from a boat.
Older 'scarback' individuals may have large areas of unpigmented skin on
the back above the pectoral fins. Flippers are short (up to 420 mm,
average 330 mm) and, unlike those of the West African Manatee
*Trichechus senegalensis*, lack nails.

Hind flippers are absent. Fluke is triangular, like that of a whale,
unlike that of manatees (*Trichechus* spp.), which have a paddle-shaped
tail.

Dugongs exhibit little sexual dimorphism in size. Anal and genital
apertures are contiguous. Testes are abdominal. Two mammary glands, each
opening via a single teat, are situated in the 'armpit' or axilla;
mammaries are somewhat reminiscent of the breasts of human.

Tusks of mature erupt on either side of the head for up to about 30 mm.

Molar teeth are simple and peg-like. A Dugong has a total of six cheek
teeth (premolar and molar) in each quadrant of its jaw during its life,
but these are never all erupted and in wear simultaneously. Three
premolars are present at birth; old
[animals](https://simplyecologist.com/how-to-study-animals-in-the-wild/)
have only two pairs of teeth (molars two and three), and these may grow
throughout life.

The Dugong's closest living relatives in the order Sirenia are the
manatees of the family Trichechidae, but no members are sympatric.

## Distribution {#distribution .wp-block-heading}

African range extends from the Red Sea and the Gulf of Aden to
Mozambique and Dugongs have been recorded as vagrants as far south as 50
km north of Durban, KwaZulu-- Natal. There is little information on
current Dugong distribution and abundance along the African Red Sea.
Dugongs have been reported off the coasts of Egypt, Sudan, and Djibouti,
Somalia, and, based on anecdotal reports of live sightings and the
location of skulls, are thought to occur in most areas along the coast
of Eritrea. In 2003 and 2004, information was collated through
literature reviews, questionnaire surveys, and opportunistic sightings,
and confirmed the continued existence of small numbers of Dugongs in
Kenya, Tanzania, Mozambique, Madagascar, Seychelles, and the Comoros
Archipelago and established the regional significance of the Bazaroto
Archipelago in Mozambique as important Dugong
[habitat](https://simplyecologist.com/what-is-the-natural-habitat-of-a-red-panda/).

Dugongs have disappeared from Mauritius and are believed never to have
occurred in Réunion. Extralimital to the African
[continent](https://simplyecologist.com/what-continent-has-the-deadliest-animals/)
and the Red Sea region, the Dugong has a range that spans at least 40
countries and territories in tropical and subtropical coastal and island
waters including the Arabian Gulf, the coast of India and Sri Lanka,
South-East Asia, Taiwan, north to Okinawa in Japan, and east through
Papua New Guinea to Vanuatu, between about 26 and 27° north and south of
the Equator. Their historic distribution is believed to have been
broadly coincident with the tropical Indo-Pacific distribution of its
food plants, the phanerogamous sea-grasses of the families
Potamogetonaceae and Hydrocharitaceae.

## Habitat {#habitat .wp-block-heading}

Dugongs frequent coastal waters. Large concentrations of Dugongs tend to
occur in wide shallow protected bays, wide shallow mangrove channels,
and in the lee of large inshore islands where there are sizeable
sea-grass beds. Dugongs are also regularly observed in deeper water
further offshore in
[Australia](https://simplyecologist.com/what-continent-has-the-deadliest-animals/)
in areas where the continental shelf is wide, shallow, and protected,
and where deepwater sea-grass beds occur. Dugong feeding scars have been
observed at depths of up to 33 m in sea-grass beds in the Great Barrier
Reef region. Around the Lamu archipelago, fishermen reported that Dugong
used to be numerous in deeper waters beyond the reef during periods when
the sea was calm (Nov--Mar) where they were believed to be feeding on
*Syringodium* and C*ymodocea ciliata.*

When the sea became rough, Dugongs moved into shallower, more sheltered
bays within the reef, at which time they were feeding on Halophila and
*Zostera* spp. and *Halodule uninervis*.

The number of Dugongs worldwide is unknown, but there are likely to be
more than 100,000 individuals. However, this rather large number is
somewhat deceptive if one considers the conservation status of Dugongs
in particular countries. Of this estimate there are likely to be some
85,000 animals in Australia and several thousand in the Arabian Gulf;
however, in many parts of the species' original range, Dugongs survive
only in very small numbers (i.e. a few tens or hundreds of individuals).

## Adaptations {#adaptations .wp-block-heading}

Dugongs are highly adapted to the marine environment in which they spend
their entire lives as evidenced by their relatively large size,
streamlined body, whale-like tail, paddlelike forelimbs (flippers), and
absence of hindlimbs. In common with other sirenians, the skeleton of
the Dugong is comprised of extremely dense bone that presumably
functions to the frontal view of Dugong muzzle showing bristles around
the oral cavity and intermaxillary rostrum.

Body hair is sparse but the hairs and bristles on the Dugong's head,
particularly around the lips and mouth, are highly developed sensory
organs that presumably help Dugongs detect their sea-grass food. The
Dugong's mouthparts are highly adapted to bottom-feeding on vegetation
and the mechanism whereby the muzzle and lips 'rake' food into the
mouth.

The two nostrils are on top of the anterior end of the snout, which
allows the Dugong to breathe with very little of the head above the
water. The nostrils cannot be closed completely, but the contraction of
muscles surrounding the nasal ducts closes the ducts. The eyes have no
eyelids but are protected by nictitating membranes and are lubricated by
oil glands.

## Foraging and Food {#foraging-and-food .wp-block-heading}

Dugongs are sea-grass specialists, uprooting whole plants when they are
accessible leaving long serpentine furrows bare of sea-grass in
sea-grass meadows. When the whole plant cannot be uprooted, they feed
only on the leaves. In some places, Dugongs prefer 'weedy' or 'pioneer'
species of sea-grass, especially species of the genera Halophila and
Halodule; *Halodule uninervis* is mentioned in most studies that have
investigated the diet of the species in the African range. These sea
grasses are low in fiber, high in available nutrients, and easily
digested.

Thus, deep water sea-grasses, notably Cymodocea and Syringodium, are
allegedly preferred by Dugongs Nov--Mar, when seas are calm and warm,
while shallow-water, in-shore species such as Halodule, Halophila, and
Zostera are apparently grazed Apr--Oct, when the sea, off-shore, is very
rough and cold and avoided by Dugongs.

Dugongs are known to practice coprophagy, at least in captivity, and
they have been known to feed on invertebrates in some areas. Dugongs
have an enlarged hindgut with a rich microflora enabling them to digest
cellulose and other fibrous carbohydrates; they retain low-fiber
material for extended periods of time within the long, tubular hindgut
thereby digesting all the fibrous material.

## Movements {#movements .wp-block-heading}

Local movements were generally tidally driven and represented commuting
between and within sea-grass beds. Large-scale movements were rapid and
apparently directed at reaching a specific and distant site.
Radiotracked Dugongs that were traveling rarely were far from the coast.
Some animals caught close to the high latitude limits of the Dugongs'
range on the Australian east coast in winter apparently undertook
long-distance movements to escape water temperatures less than about 18
°C .

Overall, the Dugongs spent about half of their daily activities within
1.5 m of the sea surface and 72% in less than 3 m. Their mean maximum
dive depth was 4.7 m, the mean dive duration was 2.6 min, and the
average number of dives per hour was 11. The maximum dive depth recorded
was 20.5 m, the maximum dive time in water \>1.5 m was 12.3 min.

## Reproduction and Population Structure {#reproduction-and-population-structure .wp-block-heading}

Studies in Australia indicate that Dugongs are long-lived with a low
reproductive rate, long generation time, and a high investment in each
offspring. Females do not bear their first calf until they are at least
six years of age and up to 17 years old. Gestation is approximately 13
months. Usual litter size is one; Dugongs only rarely give birth to
twins. Neonates are 1.1--1.25 m in length (n = 18) and weigh 27--35 kg
(n = 53). The calf suckles for 18 months or so, and the period between
successive births is very variable; estimates range from 2.5 to 7.0
years.

Dugongs start eating sea grasses soon after birth and grow rapidly
during the suckling period. Population simulations indicate that a
Dugong population is unlikely to be able to increase in size by more
than 5% per year. This makes the Dugong highly susceptible to
over-exploitation by humans. Bodyweight at puberty is about 250 kg.

The oldest Dugong was estimated to be 73 years old when she died.

## Predators, Parasites and Diseases {#predators-parasites-and-diseases .wp-block-heading}

Given Dugong's life history, natural mortality rates must generally be
low. In Australian waters, there are reports of Dugongs being attacked
by sharks,
[killer](https://simplyecologist.com/what-animal-is-the-fastest-killer/)
whales, and crocodiles. Dugongs are susceptible to a wide range of
diseases, some of the infectious or parasitic ( describes a range of
Dugong parasites.

Conservation IUCN Category: Vulnerable A2bcd. Dugongs are afforded
legislative protection in most countries in the region. However, most
governments have neither the resources nor the capacity to monitor all
activities in the marine and coastal zones. The fact that Dugongs range
across national borders argues for the
[development](https://simplyecologist.com/birds-reproduction-and-development/)
and implementation of regional and international conservation efforts.


Synonyms: australis, cetacea, dugung, hemprichii, indicus, lottum, tabernaculi. Chromosome number: 2n = 50.  Measurements; 2.4 (2.2–3.31) m; n = 18 WT: 250–570 kg Description   Rotund cetacean-like body with flippers and flukes that resemble those of a dolphin without a dorsal fin. Head resembles that of a walrus without the long tusks. Head distinctive, with mouth opening ventrally beneath the broad, flat muzzle.

Messaggi di Rogue Scholar

Facts about the dugong