This summer, as in the summer of 1994, a strange and exotic creature graced the Bay waters. Not normally found farther north than North Carolina, a West Indian manatee swam from Florida to Chesapeake and Delaware bays, then along the New Jersey coast to New England. No one knows why this manatee, affectionately known as Chessie, strayed so far from its natural habitat. But all who have seen him are intrigued with the gentle giant.
Manatees are marine mammals that belong to the order Sirenia, from the word siren. In Greek mythology, sirens were creatures who lured sailors to treacherous, rocky shores with their songs. There are four species that belong to this order: the dugong, found in the coastal waters of the Indian and Pacific Oceans; the West African manatee, found in the coastal waters and rivers of western Africa; the Amazonian manatee, found in the fresh water of the Amazon basin; and the West Indian or Florida manatee, found from the southern United States to northern Brazil. A fifth species, the Stellar’s sea cow, was hunted to extinction by 1768. This unique mammal of the Bering Sea grew to more than 30 feet long and ate marine algae.
Manatees and dugongs evolved from four-footed land mammals; evidence of this is the presence of an undeveloped pelvic bone. Their closest relatives are elephants and small Asian and African mammals known as hyraxes.
The Florida manatee is found primarily along the coast of Florida. Most adult manatees are about 10 feet long and weigh 800 to 1,200 pounds, although some manatees have grown larger than 12 feet and weighed 3,500 pounds. Manatees have a tough, wrinkled brown to gray skin that is continually being sloughed off. Hair is distributed sparsely over the body. With stiff whiskers around its mouth, the manatee’s face looks like a walrus without tusks.
The manatee maneuvers through the water by moving its paddle-like tail up and down and steering with its flippers. Manatees are very agile for large animals, sometimes somersaulting and doing barrel rolls in the water.
Although the manatee can remain underwater for as long as 12 minutes, the average time is 4 minutes. Manatees often rest suspended just below the water’s surface with only their snouts above water. As herbivores, manatees eat only plants. They feed underwater, along the water’s edge and may forage on overhanging vegetation. In the Chesapeake Bay, manatees might graze on submerged aquatic vegetation such as pondweeds, wild celery, widgeon grass and eelgrass as well as emergent vegetation such as smooth cordgrass. Manatees must eat 10 percent to 15 percent of their body weight daily. To do this, they spend six to eight hours a day eating.
The manatee spends its life moving between freshwater, brackish and saltwater environments. It prefers large, slow-moving rivers, river mouths and shallow coastal areas such as coves and bays. Great distances may be covered as the animals migrate between winter and summer grounds. During the winter, Florida manatees congregate around warm springs and power plants that discharge warm water. During summer months, some manatees move north, mainly into Georgia and the Carolinas (with the exception of Chessie).
Female manatees are not sexually mature until they are 5 to 9 years old. Males are mature at about 9 years of age. The gestation period is approximately 13 months. Usually only one calf is born every 2 to 5 years. Twins are rare. Newborn calves weigh 60 to 70 pounds and are about 4 feet long. They nurse from a nipple located behind the forelimb of their mother. Born with teeth, calves begin eating plants within a few weeks after birth but may remain with their mother up to 2 years.
Manatees communicate with each other by emitting sounds underwater that are audible to humans. These squeaks and squeals are especially important for maintaining contact between a mother and calf. Hunted for thousands of years, manatee meat was a food source for Native Americans and, later, the Spaniards. Bones were used for medicinal purposes. Leather made from manatee hides was prized for its thickness and used for canoes and battle shields. Missionaries used manatee oil for lamps.
The Florida manatee is a federally endangered species. Many factors have contributed to its endangered status. Humans pose the greatest threat to manatees. Speeding boats run over manatees, submerged just below the surface, killing them either by impact or by slicing into their backs with the propellers. Manatees that survive such encounters carry distinctive scars.
Sensitive manatee areas are posted with speed limits to slow boats so manatees have time to get out of the way.
Flood gates and canal locks have accidentally killed manatees either by crushing or drowning them, although modified operating procedures have reduced the number of these fatalities.
Fishing lines and other trash carelessly discarded into the water are also responsible for a few manatee deaths each year. Death may result when the manatee’s digestive tract becomes wrapped with ingested fishing line. Fishing line tightly wound around a flipper can create a serious infection and possible loss of a flipper.
Harassment from swimmers, fishermen and boaters can interrupt feeding and mating activities. Manatees may be driven into cooler water where they are more susceptible to disease and cold stress. During the winter, when manatees congregate at the Crystal River National Wildlife Refuge on Florida’s west coast, boaters, swimmers and divers are prohibited from some areas.
Natural conditions may also imperil manatees. These animals cannot survive long in cold water. Unusually cold winters can kill manatees. The minimum water temperature that manatees can tolerate ranges from 62 to 64 degrees Fahrenheit. As the water temperature drops below this range, manatees become sluggish and may stop eating. Young are especially susceptible to the effects of cold water.
Periodic outbreaks of red tide can cause some manatee deaths. Red tide is a result of a bloom of small microorganisms. Sea squirts, a filter-feeding animal associated with sea grasses, accumulate toxins from the red tide organisms. Manatees accidentally ingest these organisms while feeding on sea grasses.
Biologists count manatees from airplanes. It is difficult to obtain an exact population figure because poor weather or murky water conditions make it difficult to see manatees clearly. In 1994, aerial surveys counted a minimum of 1,822 manatees. Because the reproductive rate for manatees is so slow, the number of manatees killed by human and natural causes exceeds the number of manatees born.
As long ago as 1893, Florida passed a law to protect manatees. The Florida Manatee Sanctuary Act, passed in July 1978, established the entire State as a “refuge and sanctuary for the manatees.” Manatees are also protected at the federal level under the Marine Mammal Protection Act of 1972 and the Endangered Species Act of 1973, which makes it illegal to hunt, capture, harm or harass these marine mammals.
Though the Chesapeake is not part of the typical range for a manatee, this mammal’s presence illustrates the importance of the Bay in providing food and habitat to many wildlife species. We are fortunate that this endangered species can thrive in our waters. As Chessie swam from Chesapeake Bay to Delaware Bay and then up the New Jersey coast, many people who had never seen a manatee in the wild were able to watch this rare and graceful mammal.