Sirenians are an order of aquatic mammals that inhabit rivers, streams, wetlands and coastal waters. There are only four species of sirenians left, with one already hunted to extinction.
Sirenians need to be saved as they are truly unique animals. They are the only aquatic herbivores feeding on a diet of grasses, weeds, and water lilies, and if we lose these, we lose the chance to study unique mammals.
Christopher Columbus’s greatest discovery may not have been America but what he called mermaids on his first voyage. The mermaids that he described were manatees. These mermaids had a paddle-like tail and female human-looking breasts, looking like a cross between a hippo and a dolphin. Columbus described them as “are not so beautiful as they are painted, although to some extent they have the form of a human face.”
Dugongs were the following species discovered by European sailors as they sailed the Indian ocean. Dugongs, a relation of the manatee, were also described as mermaids.
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Species of Sirenian
There are three species of manatee and one species of dugong. They are members of the order Sirenia. The nearest relation of sirenians is elephants.
The African manatee Trichecus senegalensis lives in the rivers and coast of West Africa. The West Indian manatee Trihecus manatus lives as far north as Florida and down to French Guiana in South America. The third manatee is the Amazonian manatee Trichecus inunguis, which lives only in the freshwater of the Amazon basin.
There is only one species of dugong Dugong dugon. These only live in the ocean around the coasts of the Indian ocean and the West Pacific, from China down to Australia.
Manatees and dugongs resemble seals with streamlined bodies and flippers as their forelimbs. They propel themselves using their tail fluke, similar to whales. They are hairless and have small, round eyes placed on top of the head. Their ears and nostrils are also on top of their heads.
While manatees have a straight snout, the dugong has a downturned snout. Like the manatee, dugongs have a fluked tail, but it is divided into two flukes instead of one fluke.
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Steller’s sea cow
Unfortunately, another member of the sirenian order was hunted to extinction over 200 years ago. Captain Vitus Bering, an officer in the Russian navy, was stranded on what is now called Bering Island. A German naturalist on the same expedition, Georg Steller, discovered vast herds of animals, nine meters in length which lived in the shallow waters around the island. These were called Steller’s sea cows after the naturalist who discovered them.
The sailors killed a few of the animals and took their meat and skins to survive. Because they were so easy to catch, the news spread when the sailors were rescued of the sea cows. As the population was not very big, hunters soon came to the island and wiped them out. Within 27 years, the entire species was gone.
Not much is known about the Steller’s sea cow apart from what the naturalist wrote. They describe an animal that lived on seaweed, unique for such a large mammal. The only other animals that lived solely on seaweed were invertebrates and fish. To deal with their special diet, they must have had a specialized digestive system. However, we will never know.
Due to the freezing conditions in the Bering Sea, the Steller’s sea cow must have been well adapted to the conditions. Other species of sirenians are not adapted to regulate their body temperature even though they have large amounts of fat. Every other species lives in hot, tropical and subtropical waters, which is why they are rarely seen above Florida.
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Save the sirenians
The four species of manatee and dugong do not get the same attention as whales, seals, and dolphins. Savethemanatee.org is a fantastic charity that brings to light the plight of sirenians, but unfortunately, scientists and the media see whales and seals as more important. If manatees had the big, cute eyes that seals have, then I am sure they would share more of the attention.
Sirenians are challenging to keep in captivity, and they are shy and secretive in the wild, making it difficult for them to be appropriately studied.
Manatees and the dugong live in coastal waters and rivers and do not dive to great depths. They feed on plants, so their bodies do not need to be streamlined to swim fast or deep after their prey. They are entirely aquatic, giving birth in the water.
All three species and the dugong are protected but more needs to be done. Small communities still see them as a prize. They still feed themselves on their meat which is prized for its flavour, while the fat is rendered into oil, and the bones can be carved and the leather used.
However, because of their love of aquatic plants, they have been used to clear waterways of weeds. In Guyana, manatees are kept in the Botanic Gardens of Georgetown to keep the pools clear of plants. They have also been used in canals where they cleared a clogged canal in a few months.
However, taking these animals from their natural habitat can destroy the wild populations. With breeding taking place once every two to four years, it would be impossible for introduced animals to thrive. They need to be kept in their natural habitat.
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Diet
The diet of the manatee and the dugong is unique as they are the only fully aquatic herbivores. Because of this and the tragic loss of the Steller’s sea cow, scientists are studying them, which helps keep them protected.
While the Steller’s sea cow was unique in its seaweed diet, the remaining sirenians are almost as unique. They live on aquatic or semi-aquatic flowering plants. Those that live in freshwater have the most varied diet with grasses, pondweed, rushes, water lilies and other plants that they can find clogging up the watercourse.
Although they live mainly on plant material, they are also known to feed on fish, even stealing them from an unsuspecting fisherman’s net, sucking the meat off and leaving the bone.
Large amounts of food need to be eaten every day as the plant material has high water content. Manatees can eat up to 25% of their body weight in one day and dugongs up to 10%. Herds of sea cows will congregate, much live in their land namesake, feeding off large amounts of aquatic plants.
They use their large, rubbery lips to gather large amounts of food. The shape of the snout has adapted for where they do most of their feeding. Manatees feed mainly on floating plants, and their snout is straight. This even allows them to eat from overhanging branches. The dugong has a downturned nose allowing them to feed on the bottom of a waterbed.
Manatees keep their milk teeth until they drop out before growing their adult teeth. Due to the amount of sand and grit that they take in with their food, the teeth get worn down. Their molars are used in sequence, and as the teeth in the front wear out and fall out, new ones appear at the back of the jaw, moving the whole row forward.
Because of their feeding habits, zoologists and scientists are studying them, something that is helping them to survive. Manatees and the dugong are the only aquatic herbivores, which is strange when you think about how many terrestrial herbivores there are. Antelope, cattle, goats, sheep, hippos, horses, deer, and rabbits are just some of the many herbivores that live on land.
We need to save sirenians to study why they are so different from other animals. With the loss of the Steller’s sea cow and every loss of a species, we lose the chance to see and experience something unique.