Mermaids or Sirenia?

Mermaids or Sirenia?

OK, we're not actually talking about mermaids, but we will be talking about the lovely creatures that are believed to be the inspiration behind mermaids-the Sirenia. Sirenia is an order of mammals made up of four extant or living species. Three species of manatee exist: the West African Manatee, the West Indian Manatee, and the Amazonian Manatee. The fourth species of Sirenia is the dugong. Until about 1760, there was another species bigger than both manatees and dugongs, called the Stellar's Sea Cow. Unfortunately, the Stellar Sea Cow was hunted into extinction within 27 years of being discovered by science. We will talk more about the sea cow later in the article, though first let's look at the living creatures. 


Manatee mother and calf

Manatees are large, fully aquatic mammals. They can grow up to 4 m (13 ft) long and weigh as much as 600 kg (1300 lbs). Female manatees tend to be larger than their male counterparts. Unlike other mammals that have eyelids that close by bringing the top eyelid down, manatees' eyelids close in a circular manner, so the circle shrinks around the eye to blink. Manatees typically breed every other year as the gestation period lasts about 12 months. They also generally give birth to one offspring, which means their reproductive rate is very slow. A fascinating fact when it comes to manatees is that they have been shown to show signs of complex associative learning, on par with that of dolphins. 

An easy way to distinguish a manatee from a dugong is that all the manatee species have paddle-shaped tails. This means that the end of the tail is rounded. We'll look into what a dugong's tail looks like further in the article. 


Dugong family

The dugongs are the last surviving members of the family Dugongidae. The dugong is found in the waters of the Indian and West Pacific oceans. From the east coast of Africa all the way around the tip of southern India to the islands of the Philippines, Indonesia, and the west Pacific, including the northern waters of Australia. 

The oldest dugong on record lived to the ripe old age of 73. As adults, they have few natural predators, growing to a size of 4 m (13 ft), which is a similar size to that of manatees. The dugong, however, weighs a lot more than the manatee, coming in at 900 kg (1900 lbs). They live mainly on sea-grass but have been known to eat algae if sea-grass is scarce. 

Unfortunately, despite their long life, dugongs only reproduce a few times. It could be 7 years between births. This limits the speed with which populations can recover. 


The dugong is related to the Stellar's Sea Cow, which also belongs to the family of Dugongidae. Living in the Bering Strait, they were first described for science by Georg Wilhelm Stellar in 1741. Unfortunately, within 27 years of this, the Stellars Sea Cow was hunted to extinction. It was reported to be 9 m (30 ft) long, which would make it almost 3 times the length of the dugong. 

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