Manatees (3 species) and dugongs (1 species), often called “sea cows,” make up the four living species in the Sirenia order of mammals. These marine mammals are more closely related to elephants than to other marine wildlife. These animals are large, slow, primarily herbivorous animals that live in shallow waters.
Manatees grow up to 4.0 meters (13 ft 1 in) long and weigh as much as 590 kilograms (1,300 lb). They live in the Atlantic Ocean in coastal waters of the Caribbean, Gulf of Mexico, Amazon and West Africa. Dugongs are slightly smaller, rarely exceeding 3m (9.8 ft) and live in 40 different countries in the Indo-Pacific.
All Sirenia species are largely dependent on seagrass beds as their primary food source. Manatees move between fresh, brackish and salt water while dugongs only inhabit marine environments.
Location is the easiest way to tell the species apart, but there are some other differences. Manatees are generally larger, dugongs have a longer snout and upper lip, and their tails are very different shapes. Manatees have a paddle-shaped tail and dugongs have a fluke, similar to a whale or dolphin.
Manatees and dugongs are keystone species in their ecosystem; they are the first to indicate the health of their habitat. Their constant browsing of seagrass (up to 40kg or more per day) keeps the grasses cropped short, removes old grass and encourages new growth. Their waste provides nutrients to phytoplankton, the base of the marine food chain.
These gentle giants maintain a healthy ecosystem which provides critical habitat and feeding areas for thousands of other species, from sea turtles to tiny invertebrates.
All four species of sirenia are listed as vulnerable to extinction. Worldwide, there has been a minimum 20% decline in the last 90 years. Australia has the largest remaining population of dugongs which is still only 3-5% of historical numbers.
Natural causes of death include predation on juveniles, low water temperatures, and disease. With no natural predators for adults, the main cause of species decline is human-related. Since manatees and dugongs live in different parts of the world, their biggest threats can differ..
Seagrass meadows are the primary food source for both manatees and dugongs. Anything detrimental to seagrass ecosystems (dredging of waterways, excess sediment from coastal development, construction of seawalls, even shading from docks) also negatively impacts sirenia. The largest contributor is nutrient pollution which causes algal blooms. These blooms not only block the sunlight seagrass needs to survive, but also can have toxic effects on the nervous system of these animals.
In the first five months of 2021, nearly 750 manatees have died in Florida, mostly from starvation, as harmful algal blooms are killing the seagrass that manatees need to survive. In all of 2020, there were only 637 manatee deaths.
With no natural predators and no need to chase down prey, manatees and dugongs are slow-moving animals. This, coupled with the fact that their main food source is in shallow water, makes sirenia very susceptible to ship strikes. Collisions with boats and propellers lead to infections, disfigurement or death. Manatees are especially affected with some having over 50 propeller scars on their body.
Like all marine animals, plastic pollution has taken a toll. Fishing line and other plastics drift into seagrass beds or catch on floating vegetation and end up being consumed. Monofilament fishing line is the most common foreign object found in the digestive system of dead manatees. Dead manatees have been found with their stomach and intestinal tract clogged with plastic bags. Dugongs have similar issues. Recently, in Thailand, a rescued juvenile dugong died from shock after ingesting eight plastic bags. The plastic triggered an intestinal inflammation, which led to gastritis, a blood infection and pus in the lungs.
As mammals, manatees and dugongs need air to breathe; on average, they hold their breath for 2.5 minutes. If they are entangled while under water, they will suffocate. Discarded fishing line is frequently the problem as flippers get tangled.
Even if the animal isn’t held underwater, damage can be done. Discarded plastic packing straps and bicycle tires have been found to encircle the animal’s body and eventually imbed into flesh as the animal grows.
In North America, manatees are threatened by low water temperatures. While there used to be dozens of natural hot springs, these have been rerouted due to urbanization. These natural warm water sources were used by manatees in colder temperatures to stay warm. In the absence of these natural options, manatees have been spending their winter near artificial sources such as factory discharge. Not only is this not an ideal habitat, but bringing a large number of animals in close proximity can facilitate the spread of disease.
The reproductive strategy of these animals further complicates their ability to cope with human stresses. Manatees give birth after age three and dugongs not until ten years old. Both animals have several years between births.
Support Organizations Protecting Seagrass and Sirenia
There are a number of organizations fighting for protections for manatees and dugongs. Please support these organizations as these little-known species need more awareness. Please use your voice and spread the word about these beautiful marine mammals.
Reduce Plastic Use
Reduce the amount of trash you produce. The less we use, the less ends up on the beach or in the ocean. Carry reusable water bottles and shopping bags and say no to straws. Think about where your waste goes.
Participate in Beach and Ocean Clean Ups
If you live near the coast, volunteer or participate in beach clean-ups. Whenever you are on the beach, if you see trash, pick it up and put it in a proper waste bin. If you are a scuba diver, help with ocean clean-ups to reduce the trash circulating in the ocean.
Be a Responsible Boater
When you are operating a boat in areas known to be inhabited by manatees or dugongs, slow down to avoid strikes and, if an animal is spotted, give them at least 50m of space.
Support Manatee and Dugong Tourism
Some areas of the world are working to protect manatees and dugongs by putting a higher value on live animals through tourism. Snorkel or dive with these animals to support their protection. Make sure your guides follow procedures and local codes of conduct intended to protect the animals.
Reduce Use of Chemicals and Fertilizer
The chemicals you use on your lawn and in your home can wash into the ocean. Look for eco-friendly alternatives; and be sure to properly dispose of toxic chemicals you must use. Minimize (or stop) the use of fertilizers on your lawn or your property as these also make their way into the ocean and have negative impacts on marine life.
Do Not Feed Manatees or Dugongs
Individual tourists sometimes feed wild ocean animals in an attempt to get a closer look or to get a better photograph. These practices present a number of risks to wild animal species.
Seychelles Protects Habitat of Last Indian Ocean Dugong Population
In 2020, the Indian Ocean archipelago of the Seychelles announced the protection of 30% of its waters (twice the size of Great Britain). These waters are home to the last remaining population of dugongs in the Indian Ocean.
Jamal Galves, National Geographic Explorer
Jamal Galves is a conservation biologist and the Program Coordinator for the Belize Manatee Conservation Program. At the age of 11, Jamal joined a manatee research expedition near his village. His love for manatees was born and he has gone on to devote his life to their protection and educating others about their importance. Jamal is a beautiful example of one person spreading their passion, speaking for those who can’t speak, and making a difference.
Australia’s Dugong Population on the Rebound
Australia is home to the largest remaining population of dugongs in the world. However, in 2011, after a cyclone, the number of animals was the lowest it has been since surveys began 25 years earlier. In 2017, the count was substantially higher and 10% of the animals were calves. An encouraging sign for dugong recovery.