Michelle Simmons, Carrie Murphy, and Jo-Anne Reed

 In days past, homesick sailors often described seeing mother dugongs lying on their backs, cradling their young in their flippers to feed. This is believed to be how the tales of creatures that were half woman, half fish, inhabiting the oceans began. Dugongs once were able to travel freely in large, sociable herds, but are now more typically found alonge or in small family groups [editor's note from Dr. Young - large groups were more commonly reported in the past, but they still do occur today]. There is no certainty whether dugong populations have decreased from pre-European times, or whether they have reached critical limits for continuity. It is predicted that 40 dugong were killed each year near Wellesley Island, which are one of the most important dugong areas in North Queensland. The shark netting program to decrease the shark population off the coastal areas in northern Queensland, which has been critically important for recreational activities, has been reported to accidentally kill the dugongs. In recent times this program has been changed to long line fishing, resulting in decreased numbers of accidental drowning of dugongs (Kidd,1997).

The dugong family includes one extinct relative, the Stellar's sea cow. The Steller’s sea cow was discovered in 1741 by a crew from a shipwrecked Russian vessel called the Saint Peter. It was named after George Wilhelm Steller who collected all of the scientific data about them. The Steller’s Sea Cow grew to 8 m in length and weighted more than 6000 kg. This is 3 times the length and 15 times the weight of a dugong. They lived in cold, subartic waters and were adapted to shallower areas; therefore they could no longer dive. This made them an easy target for hunters. Steller’s Sea Cow had a small head, short neck, a split tail fluke, short stubby pectoral flippers, no teeth, and no finger bones. They were slow moving creatures that fed only upon kelp. They were often observed in small groups and became extinct 27 years later in 1768 (Reynolds, 1991).

 Dugongs are located from 30 East at the Gulf of Suez to 170 East at New Hebrides longitude and 30 North to 30 South latitude. They are found in 43 countries throughout the Pacific and Indian Ocean rims. There are 80,000+ dugongs in Australia from Moreton Bay to Shark Bay, 10,000+ dugongs in the Arabian Gulf and the Read Sea area, and very few living in the Philippines. Over 100,000 dugongs are found in these locations. There was, of course, a wider range in the past. (Rothauscher, 1998)

 An adult dugong is 8 - 10 feet in length and weights 510-1100 pounds (Rothauscher, 1998). The skeleton is made up of massive bones which are solid to aid in buoyancy. The bones of the spine are all similar in shape. The dugong has a reduced pelvic girdle shaped like a bow (Stephen, 1973). The ribs are not joined underneath to the sternum, making them floating ribs (Stephen, 1973).

 The skull of the dugong is massive and heavy boned. The rostrum is turned down. This is because the dugong is a bottom feeder (Stephen, 1973). Dugongs have no external ears, holes are only minute openings and they do have sensitive hearing (Stephen, 1973). The nostrils of the dugong are situated on the upper side of the snout. They are crescent shaped slits close together (Stephen, 1973). Their sense of smell is well developed for an aquatic animal. Their eyes have lidless slits, but they do have a nictitating or winking membrane that can be closed by skin contractions (Stephen, 1973). Dugong sight is adequate, but they rely more on hearing and their strong sense of smell (Kidd, 1997)

 The teeth of the dugong resemble those of elephants, more than cetaceans or pinnipeds (Stephen, 1973). They have both molars and incisor. The molars move forward slowly and are shed while new teeth break out in the back. The incisors of the female are short, rounded and sharp. The males are stronger and triangular (Reynolds, 1991). Male dugongs have two incisors that project from the mouth to form tusks up to 10 inches long. Most of the length of the tusks are concealed in the mouth with only an inch or so protruding (Stephen, 1973).

 The digestive system of the dugong consists of a two compartment stomach and a very long intestine. The intestine is 12-20 times the body length of the dugong. Microorganisms live in the large intestine and digest cellulose in the plant material that is eaten by the dugong (Reynolds, 1991).

The dugong uses their forelimbs for steering and balancing, and paddling for short distances. They are also used for scratching, mouth cleaning, supporting the body when resting on the bottom and embracing (Stephen, 1973).

 Dugongs have a fluked tail flipper which is used for locomotion (Stephen, 1973). The fluked tail flipper of the dugong is one difference between the dugong and the manatee. Other differences are that make dugongs have tusks and the rostrum of the dugong slants downward (Stephen, 1973).

 The average life span of the dugong is 73 years. They reach sexual maturity at 9-10 years minimum and 17 years maximum (Stephen, 1973). There is no known mating season of the dugong. Female dugongs give birth every 3 years to one calf, twins are rare. Births usually take place between September and April (Hinchinbrook Fact Sheet: Seagrasses, 1997). The pregnancy period is thought to last 11-13 months. The female dugong gives birth in shallow water and the newborn calf is able to swim to the surface for their first breath (Stephen, 1973). The babies are born a pale cream color and are 100-120 cm long and weigh 20-30 kg (Reynolds, 1991). The babies nurse for about 18 months, but some may begin eating seagrass at age 3 months (Fox, 1997). The calf will stay with the mother until she has another calf. The males are not known to stay with the stable mother calf social units (Fox, 1997). It is known that the females are good mothers who look after the calf with great care (Stephen, 1973).

 Dugongs are found in shallow waters, 3-20 m deep, and only swim to the top to breathe (Reynolds, 1991). There are no known long distance migrations made by dugongs, but some daily and seasonal movements do occur (Fox, 1997). They normally exhibit short dives of about 1-3 minutes, with a maximum of 8 minutes (Reynolds, 1991). The principal activity of the dugongs occurs in deep water about 1-5 m deep. Their average swimming speed is 10 km per hour and this can be doubled easily (Fox, 1997). Dugongs are not confined to inshore waters, they have been sighted near reefs up to 80 km offshore (Hinchinbrook Fact Sheet: Seagrasses, 1997) . They occur in herds; or in small numbers or alone where they are timid and solitary (Rothauscher, 1998).

 Dugongs feed upon seagrasses, usually Halophila ovalis. It is low in fiber, high in available nitrogen, and very digestible. Dugongs are bottom feeders and usually feed in water 1-5 m deep. The average adult consumes 25 kg per day. They feed upon marine algae when seagrasses are scarce and sometimes even eat crabs. They have poor eyesight, but they can find their food using their coarse, sensitivity bristles which cover their snout (Dugongidae, 1997).

 Predators of the dugong include humans, killer whales, large sharks, and saltwater crocodiles (Hinchinbrook Fact Sheet: Seagrasses, 1997). Sometimes tiger sharks even feed upon them, at least in some seasons during the year (Anderson, 1995).

 Dugongs communicate through soft squeaks or bird-like chirps which display frequencies in the 3-18 Khz range, which lasts about 6 seconds. These are used for terrestrial behavior or mother for calf bonding. The variability may be so they can tell each other apart. Dugongs also communicate through trills, which exhibit frequencies over a bandwidth of 740 hz, within the 3-18 Khz band lasting almost 4 minutes. They have 2-4, or even more harmonics. They also communicate through louder barking which has a frequency of 500-2200 hz, that last 3-12 seconds. They also have up to 5 harmonics, used to ward off intruders or for terrestrial defense. Scientists believe that they may produce all of these sounds in the frontal region of the head rather that in the larynx (Anderson, 1995).

 Dugongs have long been hunted for food throughout the world and they are the traditional food of the local Aboriginal people. Even though early white settlers in this area took dugong for food and "oil", this is no longer legal in Australia, now only the Aboriginal people may hunt for them (Kidd, 1997). The dugongs are protected by state and federal legislation which permits only native peoples to legally hunt them. Due to the isolated location of most dugong populations, it is virtually impossible to adequately police illegal hunting activity (Hinchinbrook Fact Sheet: Seagrasses, 1997).

 Dugongs are hunted throughout their range for meat, which has been likened to veal. They are also hunted for oil and their hides for leather (Dugong dugong, 1996). Oil rendered from their leather has been said to have curative powers (Dugongidae, 1997). Their bones and teeth are also made into ivory artifacts and charcoal for sugar refining. Some Asian cultures prize dugong products for medicinal purposes (Dugong dugong, 1996). Sea cows were prized also for meat and leather. Their aggregations and feeding behavior made them easy targets for hungry sailors (Dugongidae, 1997).

 The decrease in the dugong population is largely do to human impact. Their coastal habitat is constantly being altered and destroyed by humans. Boat collisions and maiming propellers take a few. The less direct, but major long-term problem is the disturbance of dugong from their feeding areas by noisy boat traffic. Sufficiently the biggest threat is from hunting and "accidental" catching in the gill netting of commercial fishermen. Shark nets and gill netting are known to be responsible for the drowning of hundreds of dugongs. The dugong has also become endangered by pollution, shark netting operations, illegal hunting, traditional hunting, and overhunting by poachers and Aboriginal and Torres Strait Islanders using non-traditional methods (Hinchinbrook Fact Sheet: Seagrasses, 1997). The dugong population is decreasing everywhere but in Australia, where it is protected by the government.

 Under the U.S. Endangered Species Act, as of December 2, 1970, dugongs were listed as endangered. In 1982, the world conservation union had dugongs listed as vulnerable in the red data book, meaning there is a reduction of at least 20% over the last 10 years or 3 generations, whichever is longer. In 1991, the Philippines had to have them protected in their own country. CITES, the Convention on International Trade in Endangered Species of wild fauna and flora, have them listed under Appendix I, threatened of extinction, and Appendix II which is only in Australia, not threaten with extinction at the present time, but may be if trade is not strictly controlled (Reynolds, 1991).

Anderson, P.K. and R.M.R. Barclay. 1995. Acoustic signals of solitary dugongs: physical characteristics and behavioral correlates. Journal of Mammalogy. 76:1226-1237.

Dugongidae. U of Michigan 16 Oct. 1997. http://www.oit.itd.umich.edu/protects/bio108/Chordata/Mammalia/Sirenia/Dugongidae.shtml

Dugongidae. U of Michigan 16 Oct. 1997 http://www.oit.itd.umich.edu/bio/doc.cgi/Chordata/Mammalia/Sirenia/Dugongidae/Dugong_dugong.ftl.

Kidd, David. Home page. 1997. http://www.ozemail.com.au/~man7/whales/dugongs.html.

Hinchinbrook Fact Sheet: Seagrasses. Australian Conservation Foundation seagrasses Sept. 1997. http://www.peg.apc.org/~acfenv/hinchft2.htm.

Reynolds, J.E. and D.K. Odell, 1991. Manatees and Dugongs. Facts on File Inc. New York, New York.

Rothauscher, Hans. Home page. 21 Oct 1998 http://home.t-online.de/home/rothauscher/popul_e.htm.

Rothauscher, Hans. Home page 21 Oct. 1998. Http://home.t-online.de/home/rothauscher/melles_e.htm.

Rothauscher, Hans. Home page 21 Oct. 1998. Http://home.t-online.de/home/rothauscher/dugong.htm.

Stephen, D. 1973. Dolphins, Seals and other sea mammals. Collins. London.

Sirenia. Ed. Daryl P. Domning. Apr. 1998. IUCN/SSC Sirenia Specialists http://pegasus.cc.ucf.edu/~smm/snews29.htm.

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