Sometimes known as Sea Cows, Manatees are large herbivorous marine mammals capable of moving from rivers to estuaries, and sometimes even trekking out into deeper water some distance from shore. Three of four of the living species of Sirenians are manatees; the other species is the Dugong, which is a slightly smaller and almost identical mammal living in the Indo-Pacific region. Historically hunted, along with their now-extinct relatives, these peace loving animals are threatened by man and habitat loss, not to mention pollution and climate change. Let’s take a closer look at the species and learn a bit more about ways we can help them survive into the future.
Sirenian Life
Historically, manatees living in Florida have been known to have a lifespan of up to about sixty years; a long life in the animal world. Capable of understanding and possessing a complex thought and association process, these intelligent animals have marvelous long-term memories. In studies designed to test their sensory capacities, they have been shown to possess about the same capacity for learning and tasks as dolphins and pinnipeds such as seals.
Manatees prefer marshy areas where seagrass, their main source of energy, is abundant; they inhabit coastal areas around the Caribbean and the Gulf of Mexico, West Africa, and the Amazon Basin. While manatees can move back and forth from freshwater to saltwater environments, Dugongs are solely reliant on saltwater environments.
Both manatees and dugongs require warm temperatures; they cannot survive in water below about 60 degrees Fahrenheit – this is why during the winter months, manatees move inland, to areas where warm springs feed the rivers. Manatees spend more than half their time asleep; they surface for a breath every twenty minutes or so. Normally found in water between one and two meters deep, they are particularly susceptible to injury and death from propeller strikes.
Sometimes spotted as far north as Cape Cod, and seen in Rhode Island and even New York City on occasion, manatees sometimes stray up rivers; one was found in the Mississippi River in Tennessee in 2006 although it later died in a cool lake. Commonly found in the Chassahowitzka, Homosassa, and Crystal rivers in Florida between November and March every year, manatees are also attracted to artificial heat sources; conservationists are concerned because some of the 400 or so manatees that normally migrate annually are congregating around the warm water outflows of the power plants along the coast of Florida. Some plants have closed, yet the manatees keep coming back, causing the US Fish and Wildlife Service to look for ways to keep the water warm so this group of manatees can survive.
Despite facing adversity, Florida’s manatee population is doing better than it once was. In 1996, a Florida winter survey counted 2,639 individuals; in January of 2010, that same survey counted 5,067 individuals, setting a new record and proving that intensive management and strict regulations are working. This is excellent news for this manatee population since a 1997 study showed that decreasing adult survival was pointing toward eventual extinction for the species, whose ancestral fossil record shows their precursors may have been present as long as 45 million years ago.
West African Manatees are the least studied of all manatee species; they are found in estuarine and coastal marine habitats as well as in fresh water rivers along Afrca’s west coast, from the Kwanza River in Angola north to the Senegal River, and even in Chad, 1000 miles inland. While sharks and crocodiles occasionally kill African manatees, most of the threats they face come from humans. They are sometimes poached; habitat loss and environmental disruption cause the most significant threat. Revered in some places as a mermaid type deity called Maame Water, West African Manatees are beloved by indigenous people but their populations are declining.
Dugongs exist in 37 countries; they are found in such places as Marsa Alam, Egypt, India’s Gulf of Kutch, the Andaman and Nicobar Islands, Borneo, Malaysia, New Caledonia, Vanuatu, and Borneo. They are found in the Persian Gulf as well, which supports the world’s second largest Dugong population, and an isolated population lives around Palau. Despite their widespread territory, these animals are vanishing at an almost unprecedented pace due to such phenomenon as red tides, environmental degradation, entanglement in nets, and hunting.
All Sirenians bear live young; gestation lasts for about a year. After they are born, calves stay close to their mothers for 12 to 18 months, at first nursing and later being introduced to grasses as they are weaned. Twins are unusual; most manatees are singletons. Manatees and Dugongs calve once every two to seven years.
Conserving Manatees and Dugongs
Viability studies conducted in 1997 concluded that in order for these species to survive and thrive, at least 95% of each species would need to survive to adulthood and reproduce successfully. As we have seen with the Florida manatee populations, this can be achieved with appropriate monitoring and intervention; sadly, it seems as though other populations may be much less fortunate unless nations take a stronger stance on protection.
All manatees and Dugongs are listed as Vulnerable on the IUCN Red List, with this status describing species only – some isolated populations are close to being completely wiped out. In some places, localized extinction has already occurred – Dugongs are no longer found in some places where they were once plentiful; population collapse has occurred in Hong Kong and Taiwan, and Mauritius, as well as in areas of Japan and China, Cambodia, Vietnam, and the Philippines; other areas are bright spots for the animals, they are thriving in Australia, where they are protected.
As with other marine life, Sirenians play an important role in the ecology of seas and oceans; simply raising awareness, taking special measures to prevent accidental death and dismemberment as the result of propeller strikes, and preventing entanglement by banning fishing practices that endanger them can help to preserve these gentle creatures for future generations to enjoy. When diving or snorkeling with manatees, be sure to give the animals plenty of space to reduce undue stress. Remember to look but don’t touch, and if you ever find a manatee that appears to be in distress, contact wildlife authorities immediately. As divers, we can do more than simply watch populations continue to decline. By spreading the word and helping to educate others, and by following best practices regarding the environment in other areas of our lives, we can each make small changes that can add up to create an impact.