|A dugong diving for feeding|
As shown in the chapter 'Distribution and Habitat', the population of dugongs is decreasing
almost everywhere. All causes can be attributed directly or indirectly to man, as
it seems that dugongs can well protect themselves against habitat changes, due to natural events,
because of his ability of large-scale movements. In the past years, indiscriminate hunting
has been the main threat to dugongs, in all countries. We must not forget that the most
recent relative of dugongs, belonging to the Sirenia order, has been the Steller's Sea Cow
(Hydrodamalis gigas), discovered in the Bering Sea in the 18th century and hunted to
extinction in only 27 years. While hunting has reduced generally over the years, although it has never stopped in
many countries, other threats to his survival became more and more evident, like coastal
development, fishing, habitat loss and degradation.
Let's take a look then, in details, which are the main threats to the survival of this species,
declared vulnerable to extinction on a global scale.
practiced at a large scale in the past, still goes on in many countries,
even though it's allowed only in few of them and also limited to special areas. It's an
ancient tradition, thousands of years old, because dugongs give high quality products,
like it's meat, considered as good or even better than bovine or pork. Dugong meat
is part of the traditional cuisine of many countries, including some Pacific islands.
Some populations consider this meat as a ritual dish for important ceremonies. Till 1980
it was not unusual to find dugong meat in the local markets. His meat, for many cultures, is
considered a good medicine against many kind of diseases and is also credited with
aphrodisiac properties. Hunting is made with harpoons from small boats or pirogues, or with nets,
used to capture the prey and allow it to drown.
Dugong skin is also a valuable product, thick and strong like a resistant leather, used by
populations of the Red Sea and North-East Africa to make armors, soldiers' helmets,
shields and other gears for war protection. In Egypt it was used as shoe leather.
Dugong oil had many uses: cooking, massage, fuel for lamps, as a medicine (often mixed
with its bones, burned and ground). In many places it's considered an aphrodisiac and for
this reason, in the past, has been traded to many countries. In Indonesia even his tears
(air mata) are considered an aphrodisiac. It was also used as a preservative and conditioner
for wooden boats.
Dugong tusks and bones are used as ornaments, jewelry, amulets and talismans. In some
countries, the price for dugong tusks is very expensive, increasing the hunting for trade.
It's interesting to see how, in some cultures, dugong is considered a symbol of bad luck
and for this reason not commonly hunted, except on special occasions. Other cultures,
mainly in the past, worshipped dugongs as the holder of supernatural power and hunted only
for important tribal ceremonies.
Some Australian aboriginal populations are still allowed to hunt dugongs, because it's an
important expression of their identity. [Top]
|The same specimen after few days:
- the central wound seems much better;
- he has already new scratches and wounds:
- two long scratches on its right side;
- a small wound over the right eye.
the increased fishing activity, also on an industrial scale, with the use of more and
more larger and larger nets, is the main cause of accidental dugong deaths. The
most dangerous ones are mesh and gill nets, which are used to catch sharks and big pelagics, in which
dugongs get trapped and drown. In the Moluccas, at the end of the '70s and the beginning
of the '80s, the annual average of dugongs trapped in shark nets has been estimated between
550 and 1,000 units. It's very easy to find dugong remains in the vicinity of fishermen villages.
In many Asian countries fishermen still use illegal and highly destructive fishing techniques,
like explosives and poison (sodium cyanide). These methods damage if not destroy coral reef
and associated ecosystem, including seagrass beds, the only dugong food.
In the Philippines, dynamite is directly used to kill dugongs. In many Indonesian islands
poison and dynamite are widely used. I've personally explored some islands shores and found
that at least 90% of the coral reef was seriously damaged or totally destroyed. While in
Irian Jaya, we often met fishermen with their pirogues loaded with boxes containing poison.
During many dives I clearly heard big underwater explosions. Even in Manado area,
very close to Bunaken National Park, you can hear some loud explosions at night.
Trawl nets are another threat to dugong survival, because they are also often illegally used
in shallow waters or close to shore. These nets not only kill dugongs, but damage or destroy
seagrass beds, thus reducing dugong populations. Many fishing boats don't respect international
laws, with evident habitat degradation. In Cambodia, just to make an example, fishing
is prohibited in waters less than 20 meters deep, but fishing, including trawling, is often
conducted close to shore at a depth as shallow as 1-2 meters. In many Australian locations,
close to dugong colonies, gill nets and trawling are forbidden, but the fishing industry still
accidentally kills dugongs in areas not protected. Australian authorities also have to
fight against illegal fishing boats coming from Indonesia and Taiwan. [Top]
Habitat Loss and Degradation:
in the last 50 years, habitat degradation occurred almost
everywhere, in both rich and poor countries. Industrial and building development has
altered and polluted coastal areas in the healthy countries, while the poor ones had important
urbanization, bad management of agriculture, grazing livestock on coastal dunes (like in East
Africa), loss or destruction of mangroves and other coastal vegetation, causing land erosion
and an increasing sedimentation, which covered and killed coral reefs and seagrass beds.
Egypt is a good example of coastal development which has greatly changed the habitat in
just a few years: it's enough to have a look to what happened to Sharm el Sheik where, in
30 years, it changed from desert to uninterrupted kilometers of side by side hotels.
The same happened on the African coast of this country, with many resorts and even more yards.
The Arabian Gulf, which has the second largest dugong population in the world, is at
the same time the most polluted area, because of the petroleum industry. Pollution of this
area is a serious threat to dugong survival, because seagrass health depends on water quality.
Oil business brought to an extensive coastal industrial development, including steel production,
plastics, chemicals and fertilizers, which are all products with high pollution impact.
In many countries there is more and more land reclamation. This is a major cause of
coastal erosion. Dredging for new building and constructions also means dumping of dredged
spoil into the sea, altering the ecosystem. Seagrass is very vulnerable to these changes,
because it needs clear water and light to grow healthy and productive. Many dugongs are now
living in these poor conditions and are seriously endangered.
Development in many countries also meant increased traffic of ships, ferries, boats, with
new or enlarged ports and many bays, more and more crowded, used for moorings. The result
is an increase in pollution and water turbidity.
Many ships use ballast water for their stability, filling and emptying special tanks
for this purpose, but it's hard to quantify the damage this practice can cause to
seagrass beds once these tanks are emptied of all the sediments, after a long trip.
Tourism is also a cause of habitat degradation. Today millions of people travel to
touristic locations which dump waste of all kinds into the sea.
The agricultural development, which should come to terms with the increasing population, is a cause
of pollution with the large use of chemicals and toxic herbicides and their runoff into
the sea. Andaman islands had a severe damage of the habitat after the conversion
of coastal forests into coconut and banana plantations.
Mine industry is another factor of habitat degradation, because they produce huge
quantities of sediments which can kill seagrass beds. In many Asian countries mine
plants still use illegal materials, dumping toxic waste and heavy metals into the sea
which can poison, in the medium-long period, sealife, including seagrass and dugongs.
In many areas examinations of fish reveal increased quantity of mercury, lead and other
toxic products. Mine industry causes also acoustic pollution, but it's difficult
to quantify its effect on sealife and dugongs.
In this list of causes of habitat degradation, also military bases and nuclear plants
must be included, with their dumping of hot water from reactors, which can increase
water temperature and salinity and endangering seagrass health. [Top]
even though dugongs often have an intricate pattern of scars and scratches
on their skin, which look like the ones caused by impact with propellers, the real risk of
vessel strike is low, for sure not so high as for manatees in Florida, who live in waters
with heavy boat traffic. Many manatees are killed or injured every year, so speed limits are
now enforced in many places and signs inform of their presence. Seems that dugongs, on the
contrary, learnt to cohabit with boats presence, adapting feeding time and keeping at a
safe distance. Luckily dugongs normally live in areas with very low boat traffic. In some
places, with heavy traffic, they chose to move to a quieter area. The only dangerous areas
are in Australia, near towns with many recreational boats. There, every year, some dugongs get
injured and few of them even killed.
Heavy traffic also causes water turbulence, which can affect seagrass habitat and disturb resident
Anyhow, as all threats to dugong survival, it must not be underestimated.
NB: enlargements of all these photos are available in the Photo Gallery
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