Anderson and Barclay, ; Lawler, et al. Visual communication is a useful source of communication when dugongs are in close contact. During breeding season, males perform lekking behavior, a physical display in a specific location to draw in females with which to mate. The vision of dugongs, however, is quite poor and they rely on other senses to create a mental map of their surroundings. Dugongs also utilize their sense of smell. They have an elementary olfactory system that allows them to sense chemicals in their environment to a certain degree.
This can be used to detect other dugongs, or most likely, for foraging. They can smell aquatic plants and can therefore determine where the next feeding ground should be or where to proceed on their feeding furrow. Touch is another sense that dugongs use in order to communicate. They have sensatory bristles all over their body, including many on their lip, which help detect vibrations from their surrounds.
This allows dugongs to forage more efficiently as they can sense the seagrass against their bristles. This is particularly useful as it complements their poor eyesight. Mothers and calves also engage in physical communication, such as nose touching or nuzzling that strengthens their relationship. Mothers are almost always in physical contact with their calf, the calf either swimming beneath the mother by the fin or riding on top of her.
Calve may even on occasion reach out a fin to touch their mother to gain reassurance. Dugongs are primary consumers and the only completely herbivorous marine mammals. They consume seagrass, particularly of the families Potamogetonaceae and Hydrocharitaceae in the genera Halophila and Halodule.
They prefer seagrasses that are low in fiber, high in available nitrogen, and are easily digestible for better nutrient absorption. Their long intestine aids the digestion of seagrass. They also have a low metabolism. When seagrass is scarce, dugongs also eat marine algae. They are speculated to supplement their diet with invertebrates such as polychaete worms , shellfish and sea squirts which live in seagrasses. Dugongs use their flexible upper lip to rip up entire seagrass plants. If the entire plant cannot be uprooted, they rip off leaves.
Their grazing leaves distinctive furrows in the seagrass beds that can be detected from the surface. To be supported properly by their environment for a year, dugongs require a territory with approximately 0. This area varies with individual and the extent of their movement, the amount of seagrass detected on the sea floor compared to what it actually ingested, the yearly productivities of seagrass, and the rates of re-growth of seagrass.
Dugongs have very few natural predators. Their massive size, tough skin, dense bone structure, and rapidly clotting blood may aid defenses. Sharks , crocodiles , and killer whales , however, feed on juvenile dugongs. Additionally, dugongs are often killed by humans. The are hunted by some ethnic tribes in Australia and Malaysia, caught in gill and mesh nets set by fishers, struck by boats and ships, and are losing habitat and resources due to anthropogenic activities.
Intensive grazing of dugongs on seagrass has numerous effects on the ecosystem, both directly on the seagrass and indirectly on other organisms that live in or feed on seagrass. Their grazing contributes to nutrient cycling and energy flow as they stir up sediment. Their fecal matter also acts as a fertilizer, which helps seagrass to more quickly reestablish. However, in the short term, intense grazing reduces habitats and nurseries for important commercial fish species and other invertebrates which live in seagrass.
Anderson, ; Spain, et al. Dugongs are economically valuable while alive as a form of ecotourism. Activities such as dugong-watching cruises in Australia and swimming with dugongs in the Philippines and Vanuatu help local economies. Dugongs are also hunted for a variety of reasons.
In Malaysia, dugongs are eaten opportunistically when incidentally caught in fishing nets or traps and when incidentally or purposely caught when fish bombing, a method of fishing which involves throwing a bomb into the water. Dugongs killed in these circumstances are usually consumed locally or sold to neighboring islands for a good price, as the meat is considered a delicacy.
In Australia, some native people regard hunting the dugong an integral part of their traditions. Humans eat their meat and use their oil. Dugong tusks are also used as a treatment for a variety of ailments including asthma, back pain, and shock. Tusks are also made into amulets and, in powdered form, mixed to make a drink. Smoking pipes can be carved from the tusks and the emitted smoke is said to have medicinal properties.
Dugongs provide a thriving trade between villages and islands, although trafficking dugong parts is illegal. Cabanban, et al. This threatened status is primarily due to human hunting and activities.
Dugongs are inadvertently trapped in fish and shark nets and die due to lack of oxygen. They also get struck by boats and ships. Additionally, pollution into the oceans from surrounding land kills seagrass beds and may also negatively influence dugongs directly.
Dugongs are also hunted for their meat, oil and other valuable commodities as previously mentioned. Populations of dugongs are unable to rebound in part because of their very low reproduction rate. This rate is low even despite their long lifespan and low natural mortality rate from lack of predators.
Some protected sites for dugongs have been established, particularly off the coast of Australia. These areas contain seagrass beds and optimal environments for dugongs, such as shallow water and areas in which to calve. Reports have been made assessing what each country in the dugong range should carry out to preserve and rehabilitate these gentle creatures. Dugongs belong to the order Sirenia , so named for the mammary glands akin to human breasts and their nursing behavior. Because of this, some sailors call dugongs mermaids or sirens, from which the name was created.
Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a now extinct synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds. Referring to a mating system in which a female mates with several males during one breeding season compare polygynous.
For example: antlers, elongated tails, special spurs. Adulyanukosol, K. Thongsukdee, T. Hara, N. Arai, M. Observations of dugong reproductive behaviour in Trang Province, Thailand: further evidence of intraspecific variation in dugong behavior.
Marine Biology , 5 : Anderson, D. Sea Cows and Manatees. The Encyclopedia of Mammals , Vol. Anderson, P. Acoustic signals of solitary dugongs : physical characteristics and behavioral correlates. Journal of Mammology , Vol.
Shark Bay dugongs in summer. I: Lek mating. Acoustic signals of solitary dugongs: physical characteristics and behavioral correlates. Journal of Mammology , 76 4 : Cabanban, D. Rahman, L. De Iongh, H. Kiswara, W.
Distribution The Dugong is found over a broad range of the coastal and inland waters of the western Indo-Pacific region. Feeding and diet Dugongs are herbivores, feeding exclusively on seagrasses, cropping the leaves and roots by using their broad muzzle to move the food into the mouth. Life history cycle Like their relatives, the manatees of the Americas, female Dugongs in season attract the attention of a number of males, one or two of which will eventually mate with her.
Conservation status Dugongs are considered relatively abundant in Australian waters where they are legally protected by all States and the Commonwealth. References Reynolds, J. Manatees and Dugongs. Facts on File. Marsh, H. The Dugong. James Cook University, Townsville, Australia.
Bryden, M. Dugongs, Whales, Dolphins and Seals. Dugongs are primarily herbivorous, grazing on up to 30kg of seagrass a day. They eat both day and night, locating their food with the help of coarse, sensitive bristles on their upper lip. These large creatures are found in warm water around coastlines, both north and south of the equator. They inhabit both freshwater and brackish water, where seagrass beds can be found. Australia hosts the largest number of Dugongs, with the Reef providing an important feeding ground.
Despite this, Dugongs have good memories and are able to remember specific feeding areas and return to them after travelling away. Dugongs are more closely related to elephants than other marine mammals, such as whales and dolphins.
Dugongs rarely communicate visually, due to their poor eyesight. Instead, they use sounds and physical touch. When Dugong calves need to be nursed, they suck on their flippers, almost like a child sucking on their thumb. Dugongs sing to each other all the time, using chirps, whistles, barks and other sounds that echo through the water.
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