Things You Never Knew: 8 Facts about Dugongs
Dugongs feature highly on many divers’ bucket lists and are a marine mammal many of us want to see. We are extremely fortunate to spot them here in North Sulawesi but did you know that they are behind the myths of mermaids? Or that despite being known as “sea cows” they are more closely related to elephants? Did you know that dugongs “talk” to each other? Read on to find out more intriguing facts about these amazing creatures….
1. Dugong Species
There are 4 species in the dugong family, 3 out of the 4 are manatees and only 1 is dugong: “Dugong dungon”, which is the species we have here in North Sulawesi. The only other true species of dugong (Hydrodamalis gigas) was hunted to extinction in 1767, just 36 years after its discovery. They were similar in appearance to Dugong dugon but substantially bigger with a body length of a massive 7 – 10 meters and weighing in at between 4,500 – 5,900 kilograms!
Dugongs are often referred to as “sea cows” due to their heavy, solid looking bodies. They are a greyish brown color and range in length from 2.4 meters up to 4 meters and adults weigh from between 230 – 400 kilograms. They have short, paddle-like front flipper fins and a straight tail, which they use for propulsion through the water. The tail is the feature which distinguishes them from manatees, which have a paddle shaped tail, whereas the dugongs is similar to that of a whale. Dugong’s ears are barely visible but they are thought to be extremely sensitive and compensate for their poor eyesight. Dugongs have tusks but they are only visible in mature males and extremely old females – did you know that the dugong is actually related to the elephant?!
Dugongs are a social species and found in groups which can vary in size from just 2 to 200 individuals. Pairs of dugongs found together are often mother and calf pairs. Large groups don’t stay together for long as there is rarely enough sea grass to support a big group over a long time scale. Dugongs are semi-nomadic; some will migrate long distances while others will reside around the same area for life. Their travelling is driven entirely by the availability of food.
Dugongs are ordinarily a very shy species and will allow themselves to be observed from a distance but move away if disturbed. When approached patiently and cautiously they have been shown to be quite inquisitive. We have been lucky enough to have some very close encounters here at our dive sites. Did you know that dugongs communicate with each other? Similar to dolphins they use chirps, whistles, barks and other sounds that echo underwater!
Dugongs are the only completely herbivorous marine mammal on the planet and their diet consists entirely of sea grass. They use their upper lips to uproot the entire sea grass plant rather than eating only the leaves – this leads to dugong “trails” which are like sandy pathways through sea grass beds. They have very slow metabolic rates and when sea grass is scarce they will also eat algae.
5. Mating and Reproduction
Unlike many other marine species, dugong mating is not seasonal and occurs year round. Male dugongs will form a mating train and follow one female attempting to mate with her – this is known as the “following phase” which is followed by the “fighting phase”. Fighting can occur between the males or between one of the males and the female and includes splashing, tail thrashing, rolls and body lunges. The final stage is the “mounting stage”, which is when the “deed” is done. Male dugongs mount females from underneath while the other males continue to fight for the same position, meaning a female may be mounted several times by competing males – this almost always guarantees conception.
Female dugongs do not reach sexual maturity until they are 6 years old, only produce one calf every 2.5 – 7 years and have a long gestation period of 13 – 14 months!
6. Life Cycle and Span
Dugong calves nurse (suckle) for 18 months or longer and during this time they rarely stray from their mother – they are often seen riding on the mother’s back! The calves suckle from their mothers’ mammary glands which are hidden away under her fins. They continue to remain close to their mother until between 6 and 9 years of age, at which point they will leave their mother to seek out a mate of their own. Dugongs in the wild live up to 70 years or more and their age can be estimated by counting the growth layers that make up their tusks.
7. Conservation Status
Dugongs are sadly listed as vulnerable on the IUCN Red List, endangered on the US Federal List and are also listed on Appendix 1 of CITIES (Convention on International Trade In Endangered Species). Dugongs’ threatened status is largely due to human activities; if they are caught in fishing nets and cannot surface for air they will drown – they can only hold their breath for up to 12 minutes. Sea grass is often in shallow water and they spend most of their time at around 10 meters or less so they are susceptible to boat and propeller strikes, they also suffer from lack of food in areas where pollution is an issue and in some parts of the world they are hunted. These threats combined with a low and slow reproduction rate means they need protecting.
8. North Sulawesi Dugongs
We are extremely lucky to have these wonderful marine mammals here in North Sulawesi and to see them at our dive sites. The majority of sightings tend to be around Bunaken and Bangka Island where there are sea grass patches for them to feed on. Peter’s Sponge dive site at Bangka has been an excellent spot for sightings and for observing some interesting behavior as a submerged tree log has become a scratching post for them! The best time for sightings is around sunrise and sunset but as they are such a shy species sightings are not guaranteed and are a special occasion.
Recent research has shown that the area around Bangka is considered a corridor for dugong migration from Indonesia to the Philippines – watch this space for more info as research continues.
If you have any images of dugongs that you have seen here in North Sulawesi we would love for you to forward them to us, along with the dive site name and date so we can send them on to the Dugong and Sea Grass Conservation Project.
If you’d like to come and join us here in North Sulawesi and explore some of our dugongs (and our) favorite dive sites, book a combination package between Murex Manado and Murex Bangka to maximize the diversity of marine life you will see and increase your chances of an encounter. Seamless boat diving transfers from resort to resort mean no missed diving days and the opportunity to explore some of North Sulawesi’s most remote and pristine dive sites.
If you’d like to include Lembeh in your itinerary check out our Passport to Paradise program and explore three distinct dive destinations in one trip. Epic walls, kaleidoscopic reefs and the world’s best muck diving.
For more information / to make a booking: [email protected]