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Dugong

Page history last edited by PBworks 13 years ago
The Dugong

 


Description and Rationale

 

The Dugong, also known as the sea cow, is a sea animal that lives in warm, shallow waters of the Indian and South Pacific Oceans. It is an endangered sea mammal that is rapidly becoming extinct. Are there reasons as to why people don’t care much about preserving the Dugongs? Are they harmful to sea creatures or people, hindering them from living easier lives?

 Are there ways in which the Dugong is helpful to humans? The majority of Dugongs die as a result of getting tangled in fishnets and being hunted for their meat, fat, hides and bones. Is it possible for people to avoid harming these creatures, but still get on easily in daily life? Can people use Dugongs to make their lives easier while preserving them?

 The initial purpose of this project is to find different ways in which the Dugongs can be preserved and possibly helpful to people, especially fishermen. Research will be done about the Dugong to find out how they live, how they may be harmful and/or helpful, why or how they are becoming extinct, and more. This research will be done through the use of the Internet, books, and possibly interviews with experts on the topic.

 

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Biology

 

Common Names and Synonyms

Dugong dugon is also known as the Dugong. The name dugong originated from the Malay language duyung meaning lady of the sea or mermaid. It is also known as a sea cow as it is an herbivorous mammal whose diet consists of mainly sea grass. Other synonyms include duyon (Thailand) and baboy-dagat (Philippines).

 

Classification

Kingdom: Animalia

Phylum: Chordata

Class: Mammalia

Order: Sirenia

Family: Dugongidae

Genus: Dugong

Species: Dugon

The Dugong or sea cow is a large marine mammal belonging to a group of animals known as Sirenians because in ancient times sailors who saw sea cows mistook them for mermaids (sirena). It is the only species in its family (Dugongidae), after the extinction of the Steller’s Sea Cow in the 18th century.

 

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Morphology and Physical Description

Dugongs are generally smaller than manatees, with the average adult’s length being 2.7 meters (8.9 ft), weighing from 250 to 300 kilograms (551 to 661 lb), though some reach 500kgs. The Dugong’s skin is thick, tough and smooth. They are born with a pale cream color, which later darkens to a grayish-brown color with a slightly lighter shade on its belly. Similar to dolphins, dugongs have small thin hairs sparsely scattered all over their bodies with thicker, longer bristles on their muzzle. These coarse, sensitive bristles on their upper lip on their snout help locate sea grass. Dugongs do not see well, but are believed to have acute hearing and a strong sense of smell.

Like all sirenians, the dugong has a fusiform body with paddle-like forelimbs and no dorsal fin or hindlimbs. It is easily distinguished from the manatees as it has a dolphin-like, wedge-shaped tail that is deeply notched at the midline and front flippers, which measure to around 35-45cm long. Young dugongs use these flippers for propulsion but as they grow older, their fluke-like tail is then used and flippers are used for steering. Calluses on the flippers are caused by "walking" on them or drifting across the bottom while feeding.

Their bodies are sort of cylindrical shaped, narrowing down at the front and back ends, without a distinct neck separating their heads from their bodies. Their upper lip is U-shaped; forming a flat disk-like pad with a deep cleft in the center and is very muscular. It has two ridges covered with long, stiff bristles that protrude over the down turned mouth. The lower lip and distal parts of the palate have sharp pads used to grasp vegetation, which is then uprooted with the strong upper lip. Its nostrils are located on the tips of their muzzles, midway between their eyes and mouth, and are sealable for when they submerge under water, as they have no nasal bones.

Young dugongs have two upper incisors, which then grow into shorter versions of elephant tusks. These incisors are largest in males growing as long as 10 inches. Unlike manatees, the dugong’s teeth do not continually grow back via horizontal tooth replacement. Adult dugongs have a total of 10-14 teeth, in which their molars are circular, lack enamel and have no roots.

The Dugong’s skull is small and the bones of its skeleton are pachyostotic--very thick and dense, lacking marrow making them negatively buoyant, enabling them to lie on the sea bottom without exerting energy to stay down. The less energy they use, the longer they can remain submerged between breaths - making feeding more efficient. Dugongs have the ability to control the volume of air their lungs, enabling them to rise to the surface, take a breath, and return to the bottom with no noticeable effort. Being a mammal, the Dugong has to surface from the water every 5 to 10 minutes in order to breathe air. Dugongs also have no nasal bones and their zygomatic arch, also known as the cheekbone, is thick and dense. They possibly live up to 70 years, and communicate underwater with squeaks and squeals.

 

 

Getting Food

Dugongs have relatively simple stomachs and are very particular about their diets. They prefer highly digestible sea grasses with a great amount of nutrients, like Halodule rhizomes, rich in nitrogen and poor in fibers, and Halophila, easy to digest. They are aquatic herbivores and benthic feeders that feed on the phangerogamous sea grasses of the families Potomogetonaceae and Hydrocharitaceae. These marine plants grow on the sandy sea floor in shallow, warm water. They are also known to occasionally eat algae, sometimes unintensionally eating crabs that may be amidst the grassy seabed.

Dugongs eat large amounts, leaving behind feeding trails of bare sand, as sea grass is uprooted by their extremely strong, muscular upper lip. Due to their pachyostotic bones, Dugongs are able to stay submerged in water longer, eating more. The daily consumption of dugongs is about 23-26 kg. Food consumption varied between seasons and individuals, with were major reductions in consumption by the male in November and January and by the female in August and September.

The muscular snouts of dugongs are more dramatically tapered than those of manatees. Their primary feeding mechanism is uprooting sea-grass by digging furrows in the sea-floor with their snouts. They will also go to any fresh water sources for drinking. Without these fresh water sources, many would not survive. The amount of these fresh water sources, however, are beginning to decline.

 

 

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Reproduction

Adult Dugongs become sexually active when they are at least 9 years old and females give birth to calves only once every 3-7 years. Breeding occurs throughout the year and peak months for birth vary geographically. It takes about 13 months after mating before a single calf is born. Twins may be produced but like with humans, it is rare. Females give birth underwater in shallow waters where the newborn Dugongs will immediately be able to swim up for their first breath.

Calves are about 100 to 120cm long at birth and weigh about 20 to 30 kg. For several weeks, the newborns cling to the mother's back and ride from the surface to grass beds along with the feeding mother. They stay with the mother, drinking her milk and following close-by until 18-24 months of age, although calves are known to begin eating sea grass at three months. Dugongs reach adult size between 9 and 17 years of age.

 

Environmental Factors

Dugongs are known to thrive in warm shallow waters usually being constrained to water temperatures above 18 ° C, as they graze on the seabed. In places where temperature rises for winter, it brings hard times for them and forces them to migrate. When the water temperatures in the shallow gulfs get below 18 ° C they move approximately 200 kilometers out to inshore water, where oceanic water mixes with the cooler waters of the bay, producing temperatures above 18 ° C, which dugongs need to survive. Although Dugongs can live in waters that aren’t completely fresh, they need a fresh water source nearby for drinking water. Without this, many of them wouldn’t survive.

 

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Origin and Distribution

Dugongs once covered all of the tropical South Pacific and Indian Oceans but as the population greatly decreased, the distributions are limited to certain waters that are warm, shallow and have their specific, dietary sea grasses. They mainly live in isolated channels and bays where they are sheltered from rough winds and heavy waves. Most of the world’s population of Dugongs is now found in northern Australia between Shark Bay in Western Australia and Moreton Bay in Queensland. Other places include the Philippines, Thailand, Saudi Arabia, East Africa coasts, Malaysia, Singapore, the Red Sea and other places throughout the Indo-Pacific region. Though the range was much greater in the past.

Dugongs were previously found in every island of the Philippines. They were numerous along the country's lengthy coast. There is even record of a dugong caught in Manila Bay in the 18th century. But Dugongs have now become extinct in many areas in the Philippines. Most of the remaining of the dugongs in the country can be found in Palawan. Two other areas with possible viable populations are the eastern Luzon coast (Isabela-Quezon) and southern Mindanao. There are also indications that dugongs may still exist in Bicol, Catanduanes, Romblon, Mindoro, Caluya Islands and Cuyo. They are known to be rare or extinct in the western Luzon coast, northern Mindanao, Samar and the Visayas. Though there are no population counts in the country, the population of Dugongs in the Philippines is described as sparse and low in density.

 

Importance to People

Dugongs are considered to be the most valued source of food in the northern coastal areas of Australia, culturally and socially. Almost all dugongs are harpooned at sea being hunted for their meat, which has been likened to veal. Dugong hunting confers certain social statuses on the hunters, hence its social importance. Dugongs are usually hunted for ceremonial and other special occasions within the community in places like Thailand and Malaysia. As well as being an important source of protein, dugongs are a source of oil, which is highly prized for its medicinal qualities. Some Asian cultures prize dugong products for medicinal purposes. They are also hunted for hides for leather, and for their bones and teeth, which are made into ivory artifacts and charcoal for sugar refining.

As Dugongs are rapidly becoming extinct, people from all over the world fly to Dugong inhabited places and pay to be able to see and swim with the Dugongs, as they are friendly and harmless. As Dugongs swim in herds and in clean, warm shallow waters, resorts and facilities in areas where Dugongs thrive earn much money for locals as hundreds of tourists visit yearly to see these mermaid-like creatures.

As a Dugong eats, uprooting the plants, their grazing activity alters the sea grass composition, increasing its components quality, compared to sea grass meadows that rely only on natural turnover rates for recycling and redistribution of nutrients. With Dugongs to help, people are able to increase the quality of sea grass on seabeds increasing nutrients and plant development.

 

Survivability and Endangered Status

It is evident that the dugongs have been exploited in the Philippines for a very long time. Previously being found all over the Philippines, the population has rapidly decreased in the country and worldwide. Surveys along Australia's Greet Barrier Reef reveal a crash in the populations of dugong. From a 1987 estimate of 3,500 numbers are now feared to have dropped to just over 1,700 - a decline of more than 50%. The reasons that may be caused by humans are likely to involve a complex mixture of traditional (legal) hunting, habitat loss and drowning in commercial gillnets and shark nets, oil spills, reduced water quality due to herbicides and dynamite fishingand many more. Other reasons are due to their specific diet, need for fresh water, constrainment of water temperatures and slow reproduction rate. It is said that their population growth is so slow that even without exploitation, in ideal conditions, the Dugong population can only grow by as much as 5% a year. To adequately conserve our current dugong populations a high level of protection must be given to both the Dugong themselves and their vital sea grass habitats.

 

 

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Potential Solutions

 The Dugong, today, remains a rapidly decreasing endangered species. Does the preservation of the Dugong help or hinder people, particularly those who live by areas with Dugongs, to live an easier more abundant life? As of now, it remains indefinite whether by preserving the Dugong, people will be able to preserve nature as well as benefit them in their ways of life or whether by preserving them would cause a decline in the production of things such as food and crafts including leather and ivory. Further research will need to be performed to attain information on the impact of Dugongs on the environment and people to perceive the usefulness in preserving Dugongs and the benefits for people in areas where they inhabit. Possibilities of things that can be done to preserve Dugongs are listed below along with advantages and disadvantages for people living in the areas applicable.

 

Possibility 1

One of the greatest threats to Dugongs is the degradation and loss of their habitat. As Dugongs are able to protect themselves very well against habitat changes, all of the causes of the loss of the Dugong’s habitat can be attributed directly or indirectly to man. Loss of habitat occurs for many reasons, one of the most important being the loss or destruction of mangroves and other coastal vegetation causes land erosion and an increasing sedimentation, which covers and kills coral reefs and sea grass beds. Sea grass is very vulnerable to 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

 Advantages:

o Mangroves extremely productive ecosystems that provide numerous goods and services both to the marine environment and people. They are home to a large variety of fish, crab, shrimp, and mollusk species. By preserving these mangroves, locals can make fisheries to form an essential source of food for thousands of coastal communities around the world.

o Mangrove wood is resistant to rot and insects, making it extremely valuable. Many communities rely on this wood for construction material as well as for fuel. People can plant and gather wood to sell and make money for themselves.

o The dense root systems of mangrove forests trap sediments flowing down rivers and off the land. This helps stabilize the coastline and prevents erosion from waves and storms. By filtering out sediments, the forests also protect coral reefs and sea grass meadows from being smothered in sediment. They maintain water quality and clarity, filtering pollutants and trapping sediments originating from land.

o Many plants that grow in mangroves are medicinal plants. People in communities near mangrove ecosystems can collect these plants and use or sell them as medicine or use mangrove leaves as animal fodder.

Disadvantages:

• Conserving Mangroves requires minimizing pollution, which means minimizing industry around those areas leading to loss of jobs and money for people.

 

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Possibility 2

Many people around the world would pay to stay at resorts and swim with the endangered Dugongs. As Dugongs are harmless, calm, extremely friendly animals, it would be very safe to set up places for people to swim with them.

Advantages:

o With tourists visiting, locals would earn a lot of money by setting up resorts, stores and activities for people to do.

o Tourist spots require cleanliness and the preservation of species and corals.

Disadvantages:

• Tourists could disrupt the culture and peace of the place.

• The waters and beaches may get dirtier as trash may be dropped and the place will get polluted.

• Tourism can cause habitat degradation, as the Dugongs environment would be less peaceful.

 

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Possibility 3

Two great threats to Dugongs directly caused by humans are hunting and fishing. Many Dugongs die due to getting tangled in fishing nets or being hunted. Laws can be set banning certain harmful fishing nets or fishing in certain Dugong inhabited areas. Laws can also be set banning hunting for Dugongs.

 Advantages:

o People will be allowed to enjoy the peaceful zones where they can swim and do other activities that are not harmful to Dugongs.

Disadvantages:

• There will be fewer places to catch food.

• Dugongs being big and heavy, weighing up to 400kg have a lot of meat.

• Less harmful nets may be more expensive.

 

 

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Bibliography

Dugong Education and Information Strategy in Communities, Report by Barry Hunter

www.gbrmpa.gov.au/__data/assets/pdf_file/0003/2100/misc_015_full.pdf

Marine Creatures: Dugong – Information page by Bronwyn Allan

www.aims.gov.au/pages/research/project-net/marine-creatures/dugong.html

Analysis of stomach contents of Dugong stranded in the central regions of the Great Barrier Reef Park: May – June 2000, Article, Report and information on studies by Great Barrier Reef Marine Park Authority (GBRMPA)

www.gbrmpa.gov.au/corp_site/info_services/library/resources/documents/stomach_contents_report_2001_03.pdf

Information page on Dugongs by Great Barrier Reef Marine Park Authority (GBRMPA)

www.gbrmpa.gov.au/corp_site/key_issues/conservation/natural_values/dugongs

Research Publications by Great Barrier Reef Marine Park Authority (GBRMPA)

www.gbrmpa.gov.au/corp_site/info_services/publications/research_publications/

index.html

Threatened Species in the Great Barrier Reef – Question and Answer Information page by Great Barrier Reef Marine Park Authority (GBRMPA)

www.gbrmpa.gov.au/__data/assets/pdf_file/0010/2152/FSNo13-ProtectedSpecies-web.pdf

Scubabob -- Information page and dive journal by Roberto Sozzani

http://www.robertosozzani.it/Dugong/indexEN.html

Status report and action plans for countries and territories – report, journal and action steps by UNEP

 www.tesag.jcu.edu.au/dugong/doc/dugongactplan.pdf

 

Dugong Information page -- Encyclopedia by Wikipedia

http://en.wikipedia.org/wiki/Dugong

 

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