Window on Nature
By Lowell & Kaye Christie, F47246
Manatees, or, if you prefer, sea cows, are clearly warm-water creatures. That’s why they spend most of their lives in the shallow coastal waters off Florida. Long on the endangered species list, manatees are currently increasing in numbers, but the process is very slow. Their greatest threat isn’t hunger, predators, or red tide “” it’s boats.
Many manatees have been scarred for life on their backs or tails due to collisions with boat propellers. And those are the lucky ones. Such run-ins often can be fatal. Another serious hazard for manatees is swimming too close to flood-control gates or navigation locks, where they can be crushed and drown. And like so many animals, manatees also suffer from pollution and habitat loss.
These seal-like critters have features that make identification easy. Some time in their history, manatees lost their hind limbs, which were replaced by a wide tail. But manatee tails are horizontal, flapping up and down rather than left to right. Up front, instead of flippers, they have forelimbs with three to four toenails each. The forelimbs help them to maneuver in shallow water, where they spend most of their time. Flippers wouldn’t work nearly as well when crawling along the bottom of the ocean or riverbeds. Nor would they be much help when grabbing sea grass or other vegetation to feed on.
Since manatees are aquatic mammals, you might assume they are in the same family as seals, dolphins, or whales. They are in a group of marine mammals called sirenians. Like seals and whales, however, manatees must surface for air, but not very often. They can exchange 98 percent of their lung capacity in one enormous breath. When active, they breathe every few minutes; when resting, every 10 to 15 minutes suffices.
Typically, manatees grow to be approximately 10 feet long and weigh somewhere between 1,000 and 1,800 pounds. The occasional manatee can reach a length of 13 feet and weigh up to 3,000 pounds.
Female manatees reach sexual maturity at approximately 5 years of age, while the males may take several years longer. Adult females may breed as often as every two years, delivering a calf 12 to 14 months later. After birth, the youngster stays close to its mother for several seasons. Manatee calves weigh close to 40 pounds and are 3 to 4 feet long. They grow so quickly that they may weigh 700 pounds by their first birthday. At present, manatees are thought to live 50 to 60 years in the wild.
Manatees may be gentle, slow-moving creatures, but they are always hungry. As strict vegetarians, they spend most of their waking hours eating. An average-size manatee consumes approximately 100 to 150 pounds of greens a day.
These animals spend most of their time in the warm waters of shallow rivers, bays, and estuaries along the coast, rarely venturing into water below 68 degrees. Still, when the weather turns too hot for comfort, manatees head for cooler water. Their migration schedule runs between 40 and 50 miles a day, sometimes more.
One autumn, Chessie, a much-written-about long-distance manatee migrant, had to be rescued from the cold waters of Chesapeake Bay. Experts decided that it was too late for Chessie to migrate all the way back to Florida before winter set in, so they arranged transportation to get him back to where he belonged. Then before releasing Chessie, they tagged him with a locating device so they could track any future adventures. It revealed that Chessie swam as far north as Rhode Island during several hot summers.
But how can manatees find their way during the darkest nights, or when in murky waters? One thought is that they navigate using their sense of touch. Thanks to the sparse thatch of hair that covers their entire body, and those long, thick whiskers on their faces, they literally feel their way along. At least that’s one theory.
Manatees hear very well, even though they have no external earlobes. So far, scientists have found no evidence that the animals use echolocation in their travels. Thus, they are left with the assumption that migrating manatees probably stay close to the shoreline.
They may be serious long-distance swimmers, but manatees are also known to take a break for play, body surfing, or doing barrel rolls before getting back to business. They also squeak or squeal underwater to demonstrate stress or fear. Manatees aren’t what you would call noisy critters, but when they do make sounds, they are within the human auditory range. So if you are around manatees much, you might be lucky enough to hear their vocalizations.
As mentioned earlier, the greatest hazard to manatees is colliding with the boats that share their shallow water habitat. Homosassa Springs Wildlife State Park is one refuge for injured or orphaned manatees. Those in need of critical care are housed, fed, and given veterinary attention. Animals that can be expected to re-acclimate to life in the wild are released when ready. Manatees that are more severely or permanently injured must be kept in captivity. This month’s “Baker’s Dozen” column covers 13 places where folks have a good chance of seeing manatees, whether captive or free.