Although their bulbous, whiskery face makes this hard to believe today, manatees are probably the source of legends about mermaids. Their humanlike eyes must have captivated the early European sailors who caught fleeting glimpses of them swimming in the warm waters of the West Indies.
In the 17th century, mermaids were depicted with their male companions, mermen. Although the legends of these half-fish, half-human creatures have lived on for hundreds of years and are still popular today, it is uncertain whether the manatees that inspired the legends will live on much longer.
Only a concerted effort to protect them in their marine habitat will save manatees from extinction.
Range and Status
Manatees inhabit warm waters of the Western Atlantic from Florida to Brazil where they live in coastal waters, freshwater inlets, and river mouths.
Warm Florida waters have provided wintering refuges for manatees in natural warm water springs. They also are attracted to the warm water outflow from power plants, where on occasion a manatee has gotten stuck and rescue efforts have made the evening news.
Although their range is quite large, manatees today exist only in a few small, isolated populations. They once were widespread in rivers and along coasts in their range, but they were hunted extensively in the 18th and 19th centuries. Coastal development has further reduced their populations. Today, there are less than 2,000 manatees remaining in the United States.
The manatee is a large, bulky aquatic mammal with flippered forelimbs and a spatula-shaped tail. Manatees can grow to 12 feet in length and weigh up to 3500 pounds. They may live to be 50 years old.
The manatee diet consists entirely of vegetation, consuming at a rate of 100 pounds a day. They eat by using their divided upper lip, which is very flexible, to grasp and take in aquatic plants. Like other air-breathing marine mammals (dolphins, whales, and seals), manatees must periodically surface for air.
Females reach sexual maturity between five and nine years of age, but they do not produce many offspring; more animals are killed each year than are born. Mothers are strongly bonded to their calves, but other social ties among manatees are very loose. They are extremely gentle and have been described as incapable of aggression.
Manatees are one of four living species in the Order Sirenia, which also includes the West African manatee, the Amazonian manatee, and the dugong. Another sirenian, the Steller's sea cow, became extinct in the 1700s. The sirenians evolved from an ancestor they share with the elephant, their closest living land relative.
Causes of Endangerment
The manatee has no known predators other than humans. In the past, humans hunted manatees extensively for their meat, fat, and tough hides. In some parts of the Caribbean and South America, manatees are still hunted for food.
Powerboats are now the greatest threat to manatees. Manatees are slow, near-surface swimmers, and the number of collisions with motorboats is increasing at an alarming rate.
In 1990, 218 manatees, which comprised 12 percent of the United States' manatee population, were killed in boating accidents, and many more were injured. A recent project to capture, tag, and release manatees revealed that many bore the scars of encounters with speed boats.
Residential and commercial development along rivers and waterways has also affected the manatee population. Habitat destruction has damaged the estuarine seagrass communities on which manatees depend. In addition, chemical pollution has impaired the immune systems of marine mammals, and the manatees may have become more vulnerable to infection as a result.
Recent mass deaths among marine mammals have been traced to greater disease vulnerability due to chemical pollution. In 1988, over 10,000 harbor seals died in Denmark and Sweden from a virus related to canine distemper. PCB's (polychlorinated biphenyl) in the water contaminate the fish that the seals eat. The PCB's accumulate in the seals and make them more susceptible diseases.
Other pollution-related mass deaths have occurred recently in bottle-nosed dolphins in the Gulf of Mexico (1988) and striped dolphins in the Mediterranean Sea (1991).
Sadly, manatees seem to be experiencing an epidemic too. Since the beginning of 1996, more than 250 manatees have been found dead in southwestern Florida. With their population already severely reduced due to other causes, a single epidemic such as this could push the manatee beyond the point of no return, into an extinction vortex.
The spread of the disease may have been facilitated by the gathering of manatees at the warm-water outflows of power plants.
Manatees have been protected for an unusually long time. The English declared Florida a manatee sanctuary in the 1700s and hunting manatees was prohibited. Sanctuary from hunters has not protected the manatee from speed boats, however. Speed limits in waterways can help manatees by giving them enough time to avoid collisions and reducing the severity of collisions when they do occur.
Manatees spend hours grazing underwater everyday, and they can be very exciting to watch in their natural habitat. Manatee-watching tourism gives local people a financial incentive to preserve the species, since tourists spend their dollars at local businesses. Tourists may be inspired to do something to help these beautiful and mysterious creatures.
In Belize, manatee-watching tourism has been a very successful conservation action. Not long ago, local people hunted manatees with rifles, while today manatees are a big attraction for tourist dollars. Unfortunately, the boats that take passengers out to view the manatees have become an increasing threat. Collisions with motor boats are becoming more common and are an increasing cause of manatee mortality in Belize.
More scientific research is needed to understand manatees and their needs. One current study is tracking manatees by satellite to learn more about where they go and what they do. We need to know more about their calving and feeding behaviors.
Citizens are helping to preserve manatees through the Save the Manatee Club, an organization co-founded by singer-songwriter Jimmy Buffet. Citizen involvement also has been an important factor in tracking the recent wave of manatee deaths in Florida. Reports from concerned people are helping scientists study and understand the causes and effects of the epidemic.
Questions For Thought
Tourists travel to Belize and pay money to see manatees feed in their natural habitat. Tourists also come to see manatees displayed in marine parks such as Sea World. What different impacts do these two types of tourism have on manatee protection?
The avoidance if boating accidents is one of the most important precautions for manatee survival. What kind of a program would you design to educate boaters about manatees?
Activities: [CS1-1,CS1-8,C3-2, General]
Words in bold italics can be found in the glossary.