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Dugong - Distribution and Habitat

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Dugong distribution map
The dugong distribution

This map shows the known distribution of the dugong. As you can see, it is vast and includes at least 37 countries, in tropical and sub-tropical zones, from the Red Sea to the Vanuatu islands (Western Pacific Ocean) between 26 and 27 degrees North and South of the Equator.
It is very difficult today to estimate the surviving population of the dugong: accurate surveys have only been made in limited areas and are often years old. Surely today's population is lower than in the past, even though no historical data is available to evaluate the reduction or the territorial fragmentation.
Nevertheless, a positive sign is the fact that the dugong is currently still present at the extreme limits of its historical distribution. It should be also be considered that the methods used to gather the data calculate by defect. Currently, aerial surveys have allowed more accurate estimates and have also proven that the dugong is still present in historical zones where it was presumed extinct. For most countries and areas under study we can only count on occasional observations, accidental captures with fishermen's nets and local anecdotes.

A seagrass bed (Halodule uninervis) where
the track left by a dugong is clearly visible

Short and limited surveys have only been carried out in 14 of the 37 countries, almost always from the coast, which have allowed minimal sightings. Detailed aerial investigations have only been carried out in the Arabic Gulf and along Northern Australia's coasts, without full coverage of the areas where the dugong is present. Still, even in these countries, the information collected is not sufficient to establish a population trend, especially knowing that the dugong is able to move on a large scale, it's movement superior to that of the investigations, even though the investigations covered up to 30,000 km². What is certain is that everywhere the tales of fishermen indicate a decline in dugong population.
The distribution coincides with the existence of tranquil and protected bays, with vast meadows of seagrass of the family Potamogetonaceae, Hydrocharitaceae and Cymodoceaceae, which are the food of the dugong. Even though this is a vast area, it is impossible not to notice that it is interrupted by large areas where the dugong is not present, or limited to a few remaining survivors.

1. Western Region

Red Sea: an accurate aerial study has only taken place in Saudi Arabia in 1986 with an estimate of approximately 1.800 specimen. In the same time frame 200 specimen were estimated in Yemen, based only on fishermen's tales and accidental capture. There are no accurate studies of presence along the African coast: sightings of single animals or small groups are reported in the Gulf of Eilat, the Egyptian and Sudanese marsas (creeks along the coast with shallow waters, sandy depths and grassland), along the Eritrean coast, in the Dahlak islands and in Djibouti. Since the African coasts resemble greatly, as far as conformation and habitat, to those in Saudi Arabia, it was estimated that the population could be the same on the two coasts, bringing the total to 4,000 specimen. Maybe the incredible urbanization of the Egyptian coast was not taken into account, with its large hotels, marinas close to hotels or isolated (all obtained dredging and enlarging the natural marsas) and the development of the cruise boats, that dock in always greater numbers in the main marsas. In Marsa Alam, where a young dugong had been reported, one evening I counted 21 docked boats, each with two dinghies that went back and forth to shore.

Arabic Gulf: the second largest community of dugong, after the Australian one, is registered in this area. They are concentrated especially in the wide bay west of Qatar (with Bahrain at the center) and in Abu Dhabi. The oldest remains of a dugong, dating to 6,000 years ago, have also been found here. An aerial survey from 1986 estimates the population at 7,300 individuals. It appears that the seagrass beds along the Abu Dhabi coast represent the most important habitat for the dugongs of the region. In the winter months, herds of almost 600 individuals have been sighted. Subsequent aerial surveys in the summer of 2000 and the winter of 2001 identified 2,000 specimen, in particular in the waters of Abu Dhabi. Of these, more than 50%, were in deep waters.

East Africa - Western Indian Ocean: here one finds a fast decline of dugongs, with risk of extinction. In 1967 herds of around 500 individuals were sighted, both in Somalia and in Kenya, but now the situation has greatly changed.

Somalia: It is impossible to say what the current situation is in Somalia, because of the political situation and the guerrilla warfare that has been going on for years. The presence of dugongs is reported in the Bajuni islands and in the south of the country, with migration to and from the island of Lamu, in the North of Kenya.

Kenya: all the available information and the aerial observations confirm the gravity of the situation. In 1994 aerial surveys had spotted only 16 specimen, in 1995 total population was estimated at 50 specimen, in 1996 only 6 individuals were sighted, all in the Lamu area. The dugongs once sighted in the southern part of the country, in the Shimoni reserve, have not been sighted in the most recent aerial surveys.

Tanzania: dugongs were reported in the north of the country and a numerous and important community was present in the Zanzibar waters. According to a 1988 report, no specimen survived in the north, and no information is available for the south. It appears that they have also disappeared from Zanzibar: while in the 1990's various captures were reported, these have ceased both in 2000 and 2001. The certain sightings along the coast of the country are limited to a very few. The last certain report of dugong presence was in January 2004, when an adult female died trapped in nets, near the Rufiji river delta.

Mozambique: the situation is not any better in this country. In the 1960's, the dugong was abundant, especially in the bay of Maputo and in the bay of Bazaruto. In the 1970's there were frequent encounters with groups of 8 to 10 individuals. Now the encounters reported by fishermen are very scarce. A 1998 report limited to only 2 or 3 specimen the surviving population in the area of Maputo. In the bay of Bazaruto, on the other hand, there had been good population trends for a certain period, with an estimate of 130 individuals in 1997. But an aerial census, which WWF held in 2001, reported only 9 sightings, for a total of 13 individuals.

Madagascar: the only available information come from fishermen's observations and captures and these confirm a net decrease in dugongs. Encounters are reported in the north west and in the north east of the island, where there are vast seagrass beds. Some sightings have also been reported from the bay of Diego Suarez. It is impossible to make a quantitative estimate, since younger generations of fishermen do not know what a dugong is, and all gathered information is fragmented.

Comoro Islands: a few specimen live in the waters of the Comoro islands, with a tiny permanent community in the bay of Mayotte, at a distance of over 100 Km. from the other islands in the archipelago.

Seychelles: there are no reports from the Seychelles islands, except for Aldabra (which is some 1,000 Km. from the main islands), where the staff of the Aldabra Research Station has made four sightings in 2001, three of a single dugong and one of a couple, near the mangroves in the low waters of Bras Monsieur Clairemont. In the same area, during March 2002, researchers from the Aldabra Marine Programme made two sightings of a single individual, during a series of 5 aerial surveys in the western part of the island. These surveys also revealed the presence of a large tiger shark, in the lagoon, which represents a menace for the dugongs.

Mauritius: unfortunately it seems that the dugong is practically extinct here. Recently, a friend has told me that he has seen a television documentary regarding a dugong in the Mauritius, but I don't know when it was filmed nor have other precise information.  [Top]

2. India

In this region, the unlimited hunting that took place for many decades has almost made the species extinct. At the beginning of last century herds of hundreds of dugongs were sighted in the Palk strait and in the gulf of Mannar, between India and Sri Lanka. Research in 1983 both in the strait and along the western coast of Sri Lanka, had not spotted any dugong.

India: the only surviving population seems to exist in the gulf of Kutch, in north west India, were research from 1990 indicated a population with a prevalence of young specimen, making us think that this could be a reproductive zone. In any case, this group is very isolated from other populations, being at 1,500 Km. from the Arabic Gulf and 1,700 Km. from the strait of Palk.

Sri Lanka: until the middle of the last century, dugongs were hunted at the rate of 150 specimen per year, considering only the gulf of Mannar. The few remaining dugongs survive in this same gulf.

Andaman and Nicobar: dugongs were abundant until 1950 when they suffered a clear decline. A study made in 1999 estimated the surviving population at 100 individuals.

Laccadive and Maldive islands: unfortunately the dugong is now considered extinct here.  [Top]

3. East and South-East Asia

In this large area there are abundant habitats where the dugong could live, but again, large populations are no longer present due to hunting which takes place just about everywhere. Because of the large area, in depth surveys are very difficult and for many countries an estimate of the population does not exist, so it is hard to make a trend. As a curiosity, the name dugong comes from the Malay word 'duyung'.

Malaysia and Singapore: dugongs are present in this area, albeit in limited numbers, concentrating mostly in the strait that separates Singapore from peninsular Malaysia. Still, their numbers have never been estimated. Around the year 1970 they were considered extinct, but later aerial surveys have confirmed that a few dozen specimen have survived. In May 1999 nineteen adults and a young one were sighted during an aerial recognition flight in the islands of Pulau Besar and Pulau Rawa, in the south east of the peninsula.

East Malaysia and Brunei: an estimate of the number of dugongs is also missing for this area. Their presence is reported in the region of Sabah, in Kota Kinabalu, Kudat, Sandakan and Semporna, as well as in Brunei. Aerial surveys conducted in 2000 spotted seven groups of adults, 14 specimen in the Brunei bay and 3 of them in Kudat. The survivors are few, but it's important that dugongs have not become extinct because of hunting, which was the belief until a few years ago.

Indonesia: there is no estimate of the dugong population in Indonesia, but it's known for sure that it is present in many islands of this vast country, from Sumatra to Irian Jaya and from Kalimantan to the beaches in the south of Bali. Questioning the fishermen of many islands, I have frequently obtained confirmation of the presence of dugongs in the area, even though in constantly decreasing numbers, since it is still hunted. In many villages I have seen tusks and other bones attributable to the dugong, among which a bone with a tapered shape, locally called "brain bone", a name I cannot explain.
It appears that the most important areas for the dugong are in North Sulawesi, from Bunaken Park to the strait of Lembeh (I've seen a dugong in the island of Gangga - summer 2004), the island of Biak in Irian Jaya, the Aru islands, Flores and the region north of Timor. Individuals surveys have been carried out in areas that are too limited to allow a reliable picture of the real presence of the dugong in such a large country. The only fact is that the population have declined quickly and in some zones have even been decimated, in the course of a few years, albeit the total surface covered by seagrass beds is estimated at 30,000 Km².

Philippines: it is believed that almost all the Philippine islands have hosted dugongs, but starting in 1970 there has been a population decline. In spite of the studies that are carried out by local and international organizations, there is no current estimate of the number of dugongs. Aragones (1998) has identified the following places as the ones with the largest concentrations: the island of Palawan (including the more northern islands of Busuanga and Calauit), the north east coast of Luzon and the coasts south of Mindanao. The migration of a few groups, following the monsoons, has been reported.

Thailand: dugongs are present on both coastlines of this country: the coast of the Andamane to the west and the gulf of Thailand to the east. The western coast is the one with the largest communities. Aerial surveys conducted in this coast in 1997 and 1998 reported 50 and 38 specimen, respectively. In depth investigations in 2000 revealed, only in the province of Trang, 54 adults and 13 calves. New surveys in 2001 estimated, still in Trang, a minimum of 123 adults and 13 calves. It's interesting to note what has emerged from numerous interviews with fishermen and inhabitants of the Andamane coast: the knowledge that their well-being depends on environment health, recognizing the dugongs' importance in this balance. From the interviews it also emerged that it is a common opinion that the dugong is in decline in the areas where it was once abundant. On the other hand, a study conducted in the year 2000 has estimated 50 individuals as the surviving population in East Thailand.

Cambodia: data on dugongs is very scarce. Considered abundant until 1975, no further research had taken place due to the war and political problems, until 1990. We have news of accidental captures of a few specimen, still because of fishermen's nets, in the 1990's. A report done in 2001, based on interviews, makes us hope that a group still survives in the waters south east of the country, near the Vietnam border.

Vietnam: there are no recent reports on the population of dugongs in Vietnam, considered abundant until 1960. They were reported in the south east of the country, near the island Phu Quoc and in the islands of Con Dao, in the open sea of the Mekong delta. Estimates of the year 2000 talk about 10-20 specimen in these islands. In these same islands, from 1997 to 2000, 9 dead specimen were found, for unknown causes. Various reports suggest that there are no permanent populations, but that the dugongs migrate into the Vietnamese waters when food is scarce in other areas.

Japan: the presence of dugongs in the waters of the islands Nansei Shoto (ex Ryukyu) has been known for centuries, as attested by the findings of many of their bones in archaeological sites. Currently their presence is confirmed only in the island of Okinawa, especially along the eastern coast, from the Katsuren peninsula to Ibu Beach, in the north. Okinawa represents the northern limit of the distribution of this species. There have been some casual sightings, but no detailed research has taken place.
Aerial surveys conducted in 1979 and in 1999 in the islands of Sakishima Shoto, at the southern tip of this long archipelago, did not give the expected results, despite the abundant seagrass beds present in these islands. The dugong is therefore considered extinct in this area, taking into account that the usual traces the dugong leaves in the seagrass haven't been seen, no accidental captures have been reported after 1970 and that fishing nets are widely used in the area, acting as a menace to the survival of this species.

Taiwan: there is a lot of evidence that the dugong is practically extinct here. He was already considered rare in 1986. In the last decade no accidental captures have been reported, no sightings either, despite the increased interest in marine mammal research, starting from 1990. It should be also considered that in Taiwan there has been intense industrial and building developments, resulting in increased environmental pollution.

China: the precise situation and distribution of the dugong in China are unknown. It appears that its presence is limited to the warmer waters of the southern coast, in front of the island of Hainan and along the western coast of the latter. Researches made between 1998 and 2000 spotted some specimen both on the continental coast, in the gulf of Beihai and in the western side of this island, where it appears that the dugong population is more abundant. Once dugongs lived (maybe only seasonally) in the cold waters in front of the Pearl river estuary, beside Hong Kong, but there is no news of sightings in the past years.  [Top]

4. Pacific Islands

For almost all of these islands, dugong news is scarce and fragmented. One must add that everywhere in these area, dugongs are hunted for their meat, which is very much valued and for tribal ceremonies and other applications that are part of the traditions of these people.

Papua New Guinea: the dugong is present along all the coast of this territory and in almost all of the 600 islands that are a part of it. Surveys done in 1973-74 revealed that the largest concentrations, with groups of 20-50 individuals, were in the island of Manus, along the northern coast from the border with Irian Jaya to the mouth of Sepik river, in the island of West New Britain and from the mouth of Fly river to the south western border with Irian Jaya. In 1975, another survey on a large part of the coastline spotted 186 dugongs, with two concentrations of at least 29 and 39 dugongs at Warrior Reef, in front of Torres Strait.

Salomon Islands: there are no precise news on the presence of the dugong in this archipelago, but it has been reported in the Marovo lagoon, south of the island of New Georgia.

Palau: a small community of dugongs live on this island, at the western limit of the Carolines. Here as well a decline is noted, as indicated by aerial surveys done in 1978, 1983 e 1991, with sightings that have decreased from 34-38 specimen in the first two surveys, to 26 in the last. This community is one of the most isolated in the world, 800 Km. from Irian Jaya to the south and 850 Km. from the Philippines, to the west.

New Caledonia: little information is available for this territory as well. The presence of the dugong has been reported along the western and north eastern cost of Grande Terre, the main island and, in the year 2000, also near the estuary of the river Diahot. Local testimony confirms, in any case, its decline.

Vanuatu: these islands represent the eastern limit of the distribution of the dugong. Further east, the seagrass beds become rare or absent, acting as a limit to the expansion of this animal. There is not much information regarding dugongs of this area. An aerial survey carried out in 1987 revealed the presence of 11 dugongs, alone or as couple, including two calves with their mothers.   [Top]

5. Australia

Western Australia: in this region there are three areas with a high concentration of dugongs:

  1. Shark Bay: quantitative surveys made in 1989 and 1994 suggest a population of over 10,000 specimen, while a survey made in 1999 raises the estimate to almost 14,000 specimen. This increase is partly due to the seasonal migration process, as confirmed by satellite studies on the movements of some dugongs of this area, that have shown how the dugong is able to move over long distances to search for warmer waters. Very few specimen have been sighted in waters with a temperature lower than 18°C.
  2. Ningaloo Marine Park and Exmouth Gulf: surveys made in 1989 and in 1994 estimate the population in the Exmouth Gulf at around 1,000 specimen, with a movement inside the gulf that coincides with the seagrass beds. A subsequent survey made in July 1999 spotted fewer specimen, with an estimate of 330 individuals. Another survey done in 2000 sighted only 2 adults, too few to estimate the population size of the area. A plausible explanation is that the dugongs have migrated to Shark Bay, after hurricane Vance, in March 1999, destroyed the seagrass beds. Indeed, in the same period, Shark Bay shows a substantial increase in population.
  3. The coast from Exmouth Gulf to De Grey River: various shoreline surveys made in the 1980's confirm the existence of good concentrations of dugongs on this coast and in the islands in front of it. A quantitative aerial survey done in 2000 estimates the population at around 2,000 specimen. In all this area the seagrass meadows are very vast and should guarantee a good habitat for the future as well.

Northern Territories and Gulf of Carpentaria: for this region as well one can identify three major areas of interest:

  1. North Coast (from Daly River to Milingimbi): research in 1984 and subsequent follow-ups estimate the dugong population at 13,800 specimen, located mainly in the areas with shallow waters, near the bigger islands and in the wider bays.
  2. Gulf of Carpentaria of the Northern Territory: surveys made in 1984/85 have produced similar estimates: approximately 16,800 individuals, both in the dry season and in the wet one. Further surveys carried out in both seasons in 1994/95 indicate an average dugong population decrease of 70%. It is hard to interpret this data, given the dugong's ability to migrate over long distances, without analyzing at the same time the population along the adjacent Queensland coast.
  3. Gulf of Carpentaria Coast of Queensland: various surveys conducted starting in the 1970's identify the islands of Wellesley as the area with the greatest concentration of dugongs. The estimate in 1991 was of about 4,000 individuals. A subsequent estimate of the entire area of the coasts of this gulf, adjacent to Queensland, made in 1997, estimated the total population at about 4,200 specimen, of which about 2,650 in the islands of Wellesley. This reduction can be due to migratory factors, as the seagrass beds in this area are definitely less than in the western side of the gulf of Carpentaria.

Torres Strait and North East: today Torres Strait, that separates Australia from Papua New Guinea, represents the maximum worldwide concentration of dugongs. Through the years, various aerial surveys have been done with positive results: they estimated 13,319 (±2,136) specimen in 1987, in 1991 the estimate rose to 24,225 (±3,276) and in 1996 rose even more to 27,881 (±3,216) individuals. It can be seen that the population increase is substantial and is probably due to a migration in the examined areas from the nearby Papua New Guinea.
The north east territories include the northern part of the Great Barrier Reef: surveys conducted from 1985 to 2000 estimate the dugong population of this area from a minimum of 8,100 up to a maximum of 10,500 individuals. The differences are not significant, but it was noted during those surveys a different distribution: in 1995 the maximum concentration was at Bathurst Bay and Princess Charlotte Bay, in 2000 the greatest was a bit more to the south, at Cape Melville and Lookout Point. The dugongs prefer the waters sheltered by the barrier, but they are also present on the middle reefs. In the Great Barrier Reef the seagrass meadows go to a maximum depth of 58 meters and traces of dugong passage have been sighted up to the depth of 33 meters.
In this area there are many national parks and protected areas but some aboriginal communities are still allowed to hunt the dugong.

Urban Coast of Queensland: this denomination includes all the coast from Cooktown to Coolangatta, on the border with New South Wales region and includes the southern part of the Great Barrier Reef. Here the distribution is much more fragmented, if compared to the northern part of the Great Barrier Reef. This is due mainly to a more loose distribution of seagrass, which grows mostly in the wide, north-facing bays, protected from the south-east winds. It is hard to interpret, on the long term bases, the data provided by dugong surveys, because of migration movements. An estimate over the entire area indicates a tendency to a population decrease, while data of single locations indicate an increase.
A study on accidental deaths in shark nets, which are common in many areas between Cairn and the Sunshine Coast, would indicate an annual decline of 8.7%. This could mean that the current population has decreased to a mere 3% of what it was in the 1960's. Aerial surveys conducted in 1986/87 and 1994 indicate a population decline even in the Great Barrier Reef, with a reduction in estimated values from 3,480 to 1,680. Another survey done in 1999 indicates that the dugong population had significantly increased compared to the values of the year 1994, bringing the levels up to what they were in 1986/87.
A 1998 study indicated Hervey Bay as the area with the maximum concentration of dugongs, with an estimate of 2,200 individuals. Follow up surveys in the same area in 1992 estimated the population at only 70 individuals. In any case, it appears that a large part of the dugongs has migrated further south to Great Sandy Strait. Successive studies of the entire Hervey Bay - Great Sandy Strait area have highlighted an up and down trend, with values between 600 individuals in 1993 and 1,650 in 1999. This increase couldn't have happened without a migration, as demonstrated by the movement of some specimen, monitored by satellite.
Moreton bay, in front of Brisbane, represents another important area for the dugong. Many studies and estimates have taken place, with values ranging from 350 to 900 individuals. It is hard to compare these numbers, as surveys were carried out with different methodologies; however it is important to note that the latest studies indicate a percentage of young specimen of 10.7% and how this bay, with its islands and channels, offers a refuge in the cold months, allowing an easy exit to the ocean, where the temperature is warmer. The individuals monitored by satellite have confirmed the exit to the ocean, through the South Passage, on an almost daily basis.

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