Interesting facts about Dugongs (Dugong dugong) and Manatees (Trichechidaesp.).
Dugongs (Dugong sp.) and manatees (Trichechidaesp.) are the two existing families of the order Sirenia or sea cows. The name Sirenia comes from Greek mythology meaning mermaid. Sirenia’s are unique among all marine mammals since they are strictly herbivores. There are three living species of manatees and one of dugongs, but out of the two, dugongs were the one with most subspecies (19 in total). Up until the 1768 there was a third family of Sirenia the Steller’s sea cow (Hydrodamalisgigas) which was the closest relative of the dugong. Only 27 years after they were discovered they went extinct, making them one of history’s fastest recorded extinctions. This was most likely due to their description by Steller (after who they were named) described their blubber as almond tasting oil, creating a high demand for it especially in Russia. In Africa dugongs can be found on the east coast and manatees on the west coast (West African manatees,Tricbecbussenegalensis).
Dugongs and manatees are marine mammals with a relatively large snout, short round paddle-like flippers and horizontal tail (like whales and dolphins). They can grow to 4m in length and weigh up to 450kg. The main difference between dugongs and manatees is the shape of the tail; dugongs have a fluke tail (similar to that of a whale) whereas manatees have a rounded tail. The dugong’s mouth is turned downwards while manatees have a more centre -placed mouth. This allows the manatee to feed at any level in the water column, whereas the dugongs are restricted to feeding on the seafloor. Dugongs have been described as a cross between a dolphin and a walrus since they are more streamlined than walruses, but they have short tusks that are seen when they are feeding.
Dugongs are widely distributed in the Indo-Pacific coastal, tropical and subtropical region and can be found in 48 countries. They prefer shallow protected bays and channels, but can be found along the continental shelf in water depths of up to 33m. West African manatees are found in lagoons, rivers and estuaries from Senegal/Mauritania to Southern Angola.
Both dugongs and West African manatees have been seen giving birth all year round with a peak in June to September. Not much is known about their reproductive system, but they seem to be polygamous (https://oceanadventures.co.za/animal-relationships-work/) where the males compete for the females. Their gestations period is 13-14 months and one single calf is born. The calves will be weaned at 18 months of age, but will stay with the mother for several months after weaning. Dugongs can live for over 70 years of age, while the manatees are estimated to have a maximum lifespan of 60 years.
Both dugongs and West African manatees are classified by the International Union for the Conservation of Nature (IUCN) as vulnerable. Both are exploited for their meat, bones, skin and oil. Dugongs have also been hunted traditionally dating back 4000 years and been used in traditional medicine. Both species face several threats to their survival including being accidentally trapped in fishing nets and line as bycatch, hit by boats and through plastic ingestion (https://oceanadventures.co.za/marine-debrismarine-pollution/). They are also threatened by a loss of habitat due to the damming of rivers, clearing of mangroves and the destructions of wetlands. Despite conservation efforts to protect them they are still decreasing in numbers. Their natural predators are large sharks, Orcas and crocodiles (mainly dugongs).
– Whales dolphins and other marine mammals of the world (2006) by HadoramShirihai and Brett Jarrett. Prinston field guides 2006
– Jefferson T. Webber M. Pitman R. 2007 Marine mammals of the world: A comprehensive guide to their identification 1st edition