Dugong: The sea cow

dugong_INFOG
Art by Dana Rose Salonoy

Download the dugong module and the full size minigraphics.

Introduction

  • Scientific name: Dugong dugon
  • These mammals are strictly vegetarian and can eat up to 50 kg of seagrass every day.
  • Centuries ago, sailors mistook them for the mythical mermaids because of their ability to do “tail stands” in shallow water.
  • Considered vulnerable by the International Union for Conservation of Nature (IUCN)

Distribution

Dugongs live near the coast in areas that can support their diet of sea grass. They are sometimes found in deep ocean water but they are most often found in areas that are only up to 5 meters deep. They can be found from the waters of east Africa all the way to Australia and Indonesia. The World Wildlife Fund (WWF) has estimated that there are up to 85,000 dugongs in the world with most of them living in northern Australia.

Dugongs are found in all Southeast Asian Coral Triangle countries, which are Indonesia, Malaysia, and the Philippines or the CT3. In the Philippines, the dugong population has been greatly reduced due to hunting, pollution, and diminishing habitat. Palawan is one of the dugong’s last strongholds.

Why they are important

Dugongs help maintain productive coastal marine ecosystems by eating the sea grass that grow on the sea floor. When sea grasses are eaten it encourages the regeneration of more sea grass; studies have found that this maintains or increases the level of productivity and nutrition of marine vegetation. When seagrass gets older its nutritional content degrades; therefore constant trimming of seagrass means a healthier marine ecosystem.

Dugongs are an indicator species of whether the seagrass ecosystem is healthy or not. Seagrass meadows are vital components of the entire marine ecosystem just like mangroves and coral reefs. A single acre of seagrass can support more than 40,000 fish and 50 million small invertebrates. Seagrasses can also be called the “lungs of the sea” because one square meter of seagrass can produce 10 liters of oxygen each day through photosynthesis.

Seagrasses are very sensitive and they are often suited for clear waters and waters with low nutrient levels. Pollution from farming and industry poses a threat to the dugong because if the sea grass starts to die, dugongs will have to migrate somewhere else in search of their favorite food.

“Dugong” by flickker photos is licensed under CC BY-SA 2.0
“Dugong” by flickker photos licensed under CC BY-SA 2.0

Biology

The dugong’s eyesight is not very effective and instead it relies more on its sensitive whiskers and sense of hearing. Dugongs make chirp, whistle, and bark sounds in order to communicate with other dugongs. They use their sensitive whiskers to detect vibrations from their surroundings and they use it to search for sea grass as they swim on the sea floor.

Dugongs can live up to 70 years old and can grow up to 3 meters long and weight up to 500 kg. They have a slow reproductive cycle and will reach sexual maturity at around 6-8 years old. It takes them one year to produce a single calf. The calf often stays with the mother for up to 18 months before starting its own life.

There is little or no difference between the appearance of male and female dugongs although females may grow to be slightly larger than males.

Dugongs can only stay underwater for six minutes before needing to resurface to breathe. They are closely related to the manatee (sea cow) and are visually similar except that the tail of a manatee is shaped like a single paddle while the dugong has flukes similar to a whale.

Threats

They are overfished as people still hunt them for their meat but the dugong’s slow reproductive cycle means that the population is slow to recover and they are more vulnerable to extinction.

Dugongs are prone to threats such as boat strikes and by-catch because they like to stay in shallow coastal areas. Habitat loss due to pollution and overdevelopment are also contributing to the decline of the dugong species.

What you can do

Minimize water pollution. Don’t treat the water as a trash can; throw away your garbage properly so that the waters can remain clean. Farmers should avoid runoff with fertilizers and pesticides from reaching the water as this will pollute coastal waters and contaminate seagrass beds.

Travel slowly in shallow coastal areas. Dugongs can only stay underneath the water for a maximum of 6 minutes so this means that they will frequently surface to get a breath of fresh air. Travelling slowly  can give enough time for you and the dugong to avoid each other and prevent a boat strike.

Avoid use of mesh and gill nets in coastal areas. Dugongs can get tangled in these nets and they will quickly drown due to their small lung capacity.

Share information about our threatened resources to raise awareness about their status and their importance.

Laws that protect the Dugong in the CT3

Quiz

Without dugongs, what would happen to the marine ecosystem?

Answer by commenting on the Facebook post by CTI-Southeast Asia!

Download the Protected Philippine Aquatic Wildlife posters.

Article by Panji Brotoisworo.  Art by Dana Rose Salonoy.

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