Manatees made headlines this winter when a group of them, including a mother and calf, became marooned in a Florida storm drain and had to be rescued by marine biologists with backhoes and earth-moving equipment. Why such heavy machinery?
Manatees, nicknamed “sea cows,” can get big. Newborns average 4.5 feet long and weigh 70 pounds. Full-grown manatees weigh between 800 and 1,200 pounds, and can grow up to 13 feet in length. Slow-moving, graceful aquatic cousins of the elephant, manatees are truly gentle giants.
They are also voracious herbivores. An adult manatee can eat 10 percent to 15 percent of its body weight in algae and aquatic vegetation in a day.
With no natural predators, they can live up to 60 years or more. Loss of habitat—as the human population of the Florida peninsula grows—is the manatee’s greatest threat. Manatees need crystal-clear water, where sunlight can penetrate to power the growth of their food.
There are three major species of manatee: the West African, the Amazonian and the West Indian, or Caribbean, of which the Florida manatee is considered a subspecies. Manatees are also related to dugongs and the Steller's sea cow, which was hunted to extinction in the 1700s. One of the few megafaunal mammal species to have died out within relatively recent human history, the Steller’s sea cow serves as a stark cautionary tale of overfishing.
Florida manatees are creatures of the tropics and subtropics, where they live singly or in small groups in coastal estuaries and lagoons. Large groups, called aggregations, are only found in the winter, as they collectively search for the warmest pools, equally at ease in fresh, brackish or saltwater. They can tolerate an astonishingly wide range of salinities.
What they can't tolerate, though, is the cold. In the summer, when the water is warm, isolated individuals called vagrants have been found as far north as Massachusetts.
In 2011, a manatee spotted in the Chesapeake Bay was identified as "Chessie," the very same manatee that swam into these waters 17 years before. In the winter, when temperatures fall, manatees migrate, swimming up rivers to warm springs and even congregating around the warm-water outflow pipes of power plants.
Why do they act like such snowbirds? Manatees lack the insulating layer of blubber found in most marine mammals, like seals, walruses and whales—animals that live in cold and temperate oceans. Florida manatees are warm-weather-dependent, and their population is estimated at 6,000 today by Florida’s Fish and Wildlife Research Institute.
Scientists believe the drainpipe refugees probably came from the nearby Indian River Lagoon where, because of the South's harsh winter cold snap, the temperature in the water of their natural habitat had dropped below 70 degrees. Any temperature cooler than 68 degrees can be life-threatening.
Manatees need warm weather to survive. Changing weather patterns, and coastal pollution, threaten them. They aggregate only to warm themselves, not for a newspaper photo op—though it made for a wonderful feel-good headline. Thankfully, the 20 manatees that swam into the storm drain near Satellite Beach were rescued.
To learn more about the biology and behavior of manatees, and to see a 70-pound newborn calf, visit aqua.org/ablueview.
This is John Racanelli of the National Aquarium for WYPR, your NPR news station.