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Prepared By:
When we talk about the sea mammals the first thing which comes in minds of most of th peoples is the whale or dolphin, but have we ever thought of large, slow moving, sluggish and pretty shy creature THE DUGONG, also commonly known as SEA COW. Wild monsters or beautiful mermaids (half women and half fish), has always been the part of the stories told by sailors returning home from their sea voyages and has always fascinated us, is nothing but the dugong which is in danger due to various human activities resulting in there habitat loss. Today it is widely believed by the scientist's that the myth of mermaids was nothing but 'the dugong'. One of the biggest surprises about dugongs and their Atlantic Ocean relatives, the manatees, is what animals are their closest cousins. Both dugongs and manatees are related not to whales, dolphins, or even hippos, but to elephants.
Table 1: Taxonomic Classification of Dugong
Before putting a light on the waning populace and conservation of Dugong in Arabian Gulf , and knowing the possible causes of its annihilation, it is important to take a brief look about the biology and behaviour of this giant creature. Dugong dugon ( only living species of the family Dugongidae) are large aquatic mammals that live in warm, shallow waters belongs to order Sirenia and family Dugongidae(see table 1 for complete classification) and is found in 43 countries along the western Pacific and Indian Oceans (also known as the Indo-Pacific), with populations ranging from the coastal waters of East Africa and the Arabian Gulf to Japan, the Philippines, and Australia which has highest reported dugong population.
An adult dugong ranges in size from about 8 to 10 feet (2.4-3 m) long but both male and female can grow up to 11 feet or more in length and can weight from 500 to 1,200 pounds but some record shows of even more and can weigh over 2000 pounds . They have a streamlined body and a flat, two-pointed tail. Dugongs are usually born in a pale cream colour, but the skin gets darker to a deep slate grey dorsally and laterally as they grow older. The skin is thick, tough and smooth. The short hair is sparsely distributed over the fusiform body. The front-limbs have evolved into flippers that are 35-45 cm long. These are used for propulsion by young, but the adults use the fluke-like tail for locomotion, using the flippers for steering. Dugongs are herbivores (plant-eaters) who eat sea grasses that grow on the sea bed. They rest during the day and spend most of the night eating. The Dugong is one of the few large animals that can digest fresh sea grass. Sea grass is the dugong’s main food. So not surprisingly, it is also sometimes called the Sea Cow! A dugong often ‘cultivates’ a favourite patch of sea grass by cropping it frequently. This promotes faster growth of young tender leaves which the dugong prefers to eat. Dugongs are among few aquatic herbivores that are alive today and feed on higher plants like the phangerogamous sea grasses of the families Potomogetonaceae and Hydrocharitaceae, rather than algae. Also reported to have occasionally eat algae, and crabs have been found in the stomachs of dugongs. Even though being an herbivorous, the dugong has a relatively simple stomach. The muscular upper lip is cleft and protrudes over the down turned mouth. The lower lip and distal parts of the palate have horny pads used to grasp vegetation, which is then uprooted with the strong upper lip. Feeding, considered as the principal activity of dugongs typically occurs in water with a depth of 1-5 m. With its few bristles around the mouth it identifies and selects food. They are also extraordinary in their ability to dive for food with fully inflated lungs and to stay under water for as long as fifteen minutes. Dugongs need to eat lots of sea grass so they keep moving and are usually not permanently resident in one small location. Dugongs can travel several hundred kilometres in a few days as they feed from place to place. Breeding occurs throughout the year and a peak month for birth varies geographically. The mother dugong gives
birth in shallow waters, usually to a single calf. The calf clings to the mother’s back as she grazes. She suckles her baby for up to 18 months. The juvenile might stay with her for another year after that. It is almost impossible for the baby to survive if its mother dies. Dugongs reproduce slowly, taking 9-10 years to reach sexual maturity and give birth only every 3-7 years. They can live up to 70 years. The exact length of gestation is unknown, but it is presumed to be about 1 year. Single calves are the norm and twins are rare. They can live for 70 years, but a dugong might reach the age of 17 years before breeding. Present Status The International Union for the Conservation of Nature and Natural Resources (IUCN) lists the dugong as Vulnerable on a global scale, based on an inferred or suspected reduction of at least 20 percent over the last three generations (90 years). Except the Australian dugong population which is listed under Appendix II of CITES (Dugongs are listed as Vulnerable in Queensland , Australia , under that state’s Nature Conservation Act); all other populations are listed under Appendix I.
For more than two decades, dugongs in UAE waters have been protected by a Law of the President of the UAE (Federal Law No. 23) and Article 28/2000 Amiri Decree which prohibits the exploitation of dugongs in the UAE. In addition, a recent ban on drift net fishing in the UAE waters has helped in minimizing dugong mortalities in fishing nets (Das pers comm. 2001). Other aspects of protection of species and its habitat are under active consideration in the UAE. In response to the sighting of over 600 dugongs south east of Bahrain by Preen in 1986, a Ministerial Decree was issued also in Bahrain . This decree banned the deliberate killing or sale of dugongs (Preen 1989a). The dugong population in the Arabian Gulf is believed to be the second largest in the world after Australia . Akab Island (Umm al Qaywayn, UAE) is the oldest site (6000 years) where dugong remains have been discovered (Jousse 1999). Aerial surveys conducted in 1986 by Preen (Preen 1989a) indicated that in the Arabian Gulf , dugongs are restricted to the southern and south western coastline between Ras Tannurah in Saudi Arabia and Abu Dhabi in the United Arab Emirates . Within this area the population was estimated to be 7,307 (± s.e. 1302) animals. Baldwin (1995) suggests the sea grass habitat identified off the coastline of Abu Dhabi as the most important area in the region for dugongs. Four core areas were identified by Preen (Preen 1989a) as being the most important areas for dugongs in the Arabian Gulf :
The Environmental Agency (EAD), Abu Dhabi, conducted summer and winter aerial surveys of UAE waters in the Arabian Gulf in summer 2000 and winter 2001 (al-Ghais & Das 2001). The survey was conducted in five zones over 34 transects covering 6075km2 in summer and 6697 in winter. The population of dugongs in the survey zones was estimated to be 1861 individuals in summer and 2185 in winter. No large groups were sighted during the survey. Nearly 40% of sightings were in sea grass beds and over 50% in deep water. More than 80% of the population was sighted around the islands of Abu Al Abyad, Salalah, Marawah, Jananah, Al-Fayl, Al-Bazm and Bu Tinha (al-Ghais & Das 2001). These survey findings support Preen’s (Preen 1989a) earlier conclusions that dugongs predominantly occur in the Abu Dhabi emirates of the UAE. Threats to Dugong Survival After discussing about the biology and habitat of dugong, it is pretty well understood the reasons for the waning populace of this sluggish animal. The dugong’s natural predators are sharks, killer whales and crocodiles. But now man is the main threat, hunting dugongs for their meat, oil, skin (for leather) and for medicinal uses. Dugongs also drown when trapped in fishing nets and are injured by boat propellers. Mostly, they are threatened by the loss of sea grass habitats. Previously, dugongs used to form herds of hundreds, now groups of six are the average. Dugongs are considered highly endangered globally; listed on CITES I and considered by the IUCN to be vulnerable to extinction. In the Arabian Gulf , as in the rest of their habitat area, the dugong faces numerous threats to its survival; most of them are man made. If we talk specifically about UAE, they are threatened by the degradation of sea grass habitats caused by dredging, coastal land clearing and filling, as well as pollution. But as per the law of UAE, Dugongs are protected and can no longer be hunted, but abandoned ropes and fishing nets continue to be one of the primary causes of mortality of dugongs. Dugongs can hold their breath for roughly eight minutes. This fact, when taken in conjunction with the fact that dugongs feed in areas rich in commercially valuable fish and crustacean species, means that dugongs are at great risk of becoming tangled and drowned in fishing nets. Efforts aimed at protecting the dugong from such a fate often curtail or prohibit fishing. Gill netting is used in at least 25% of all artisanal fisheries in the Arabian Gulf . It is mainly carried out during the winter months. During surveys by Preen (Preen 1989a), it appeared that in the western Gulf, gill nets were concentrated in the Gulf of Salwa , particularly around Bahrain . Interviews with fishers in the UAE suggest that dugongs are most often caught in 14-18cm gill nets set for kingfish and sharks (Baldwin & Cockcroft 1997). A study currently conducted by the Environmental Agency (EAD) of the Abu Dhabi found that almost all reported dugong deaths are caused by gill net fishing set for large pelagic fish species (al-Ghais pers comm. 2000). There is currently no hunting of dugongs permitted in UAE waters. Fishers and local people interviewed are aware of the law banning dugong hunting (al-Ghais pers comm. 2000). Furthermore, several of the dugong's natural traits increase their vulnerability to the negative stresses resulting from human activity. The dugong's passive nature, its need to surface often, and its general habitat area all combine to make the animal vulnerable to hunting. Although hunting is not nearly the threat that it once was, the decline of the dugong throughout the world can be attributed, in part, to man's predation of the species. A close relative of the dugong, the Stellar Sea Cow, was indeed hunted into extinction in the late eighteenth century.
Due to its exclusive diet of sea grasses, the dugong is extremely vulnerable habitat loss. Scientific studies have demonstrated that where sea grass beds abound, Dugong populations tend to remain stable, whereas, when there is a scarcity of available grazing areas, dugong populations experience significant fluctuation. With the increasing population of the Arabian Gulf , has come increasing development along the coastal areas of the region. The discharge of waste and the development of coastal areas by the tourism and aquaculture sectors have tremendous negative effects on the health and viability of the area's sea grass beds, and the consequences for the dugong can be severe. One of the most constant threats posed to the dugongs of the Arabian Gulf is that of water pollution, most especially water pollution as a result of oil spills. With an enormous amount of the world ' s oil supplies located in the Arabian Gulf region, the transport of oil through the Arabian Gulf is a fact of life. So too are oil spills. Oil in the water of the Arabian Gulf destroys dugong habitats and is likely to have significant direct negative health effects on the dugong. There is also oil loading terminals in the immediate vicinity of identified important dugong areas. Furthermore, the counter-clockwise current in the Gulf means that water from the north-western section where the majority of oil extraction occurs, is likely to flow to the south-eastern section where the most important dugong habitat occurs. Sea grasses are sensitive to physical and physiological damage as a result of oil pollution (WCMC 1991). The Arabian Gulf also receives other pollutants as a result of rapid industrial development along the coastline. These industries include steel production, plastics, fertilizers and chemicals. The shallow maximum water depth (35m) and long flushing time (approx. 5 years) of the Gulf, means that there is a limited capacity for these pollutants to be absorbed and diluted (Preen 1989a). Sea grass beds in the Gulf are also under threat from trawling, land reclamation and dredging. Land reclamation is believed to be one the greatest threats to the marine environment of the Arabian Gulf . It is destroying and replacing intertidal and sub-tidal habitats, including sea grass communities. Reclamation is coupled with dredging and the dumping of dredged spoil, which may involve the direct excavation or smothering of sea grasses, or limit the growth and survival of sea grasses through increasing turbidity. Several large dredging and reclamation projects occur within important dugong habitats in the Gulf, including what is believed to be the most productive sea grass beds in the Gulf of Salwa . High salinity levels already occur in the Gulf of Salwa , and reclamation projects threaten to increase the salinity levels by impeding water flow into and out of the area. Salinity levels are also rising in the northern part of the Arabian Gulf coupled with a rise in water temperatures to 38oC. An Arabian environmental organisation suggested that indiscriminate dumping of wastewater in the region by oil companies and unchecked oil seepage may be a contributing factor to this increase in salinity (UNEP 1999). Highest priority areas for protection in ARABIAN GULF
Lower priority areas for protection in ARBAIN GULF
References
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