Aquatic Mammals

Manatee: Trichechus manatus

Appearance:

Adults are typically 9-10 feet long and weigh around 1000 pounds. However, they may grow to over 13 feet and weigh more than 3500 pounds. Adults are gray in color, with very sparse fine hairs distributed over much of the body. Stiff whiskers grow around the face and lips. Algae growing on the dermis may make them appear green or brown. They have two fore limbs, usually with 3 or 4 nails, that they use for slow movements and to grasp vegetation while eating. They have a rounded flattened tail for swimming. The nostrils, located on the upper surface of the snout, tightly close with valves when underwater. While they can hold their breath for up to 20 minutes they typically surface to breathe approximately every 3-5 minutes. Their eyes are small and have a membrane that can be drawn over them for protection. The ear openings, located just behind the eyes, are small and lack external lobes. They have a flexible upper lip that is used to draw food into the mouth.

Habitat:

The manatee is a large, herbivorous, aquatic mammal that inhabits coastal waters and rivers.

The West Indian manatee's range is from the southern United States throughout the Caribbean Islands, Central America, and to northern South America. In the United States the manatee ranges up the eastern coastline into Georgia, the Carolinas, and beyond during warm months. In the Gulf they are occasionally sighted as far west as Texas. During cold months manatees in the southern United States migrate to the warm waters of south Florida, or find a source of warm water such as artesian springs or industrial discharges.

Behavior:

They consume freshwater and marine plants of all kinds. Gestation is approximately 13 months and usually one calf is born. The calf may stay with the cow for up to 2 years. Manatees reach sexual maturity in 3-5 years and may live over 50 years.

A manatee uses its flippers and tail to steer itself through the water and moves its tail up and down to propel itself forward. Manatees are quite agile in the water. They can swim upside down, roll, do somersaults or move vertically in the water.

Manatees are mammals. They must surface approximately every five minutes to breathe, but can hold their breath for as long as twenty minutes when resting. The manatee's nose is usually the only part of its body that comes out of the water when it breathes.

Manatees are herbivores, which means they eat plants. Also known as a "sea cow," manatees usually spend up to eight hours a day grazing on seagrasses and other aquatic plants. A manatee can consume up to 10 percent of its body weight in aquatic vegetation daily. The manatee uses its muscular lips to tear plants much like an elephant uses its trunk.

Manatees rest from 2 to 12 hours a day either suspended near the water's surface or lying on the bottom, usually for several hours at a time.

Anatomy facts and trivia:

A manatee can move each side of its lip pads independently. This flexibility allows the manatee to "grab" aquatic plants and draw them into its mouth.
Manatees do not have eyelashes. Their eye muscles close in a circular motion, much like an aperture on a camera. They have a lid-like membrane (called a nictitating membrane) that closes over their eyes for protection when they are under water.
Manatees can hear very well despite the absence of external ear lobes.
A manatee's heart beats at a rate of 50 to 60 beats a minute. The heart rate slows down to 30 beats a minute during a long dive.
Manatees have no "biting" teeth, only "grinding" teeth. A manatee's teeth (all molars) are constantly being replaced. New teeth come in at the back of the jaw and move forward about a centimeter a month. The front molars eventually fall out and are replaced by the teeth behind them. This tooth replacement is an adaptation to the manatee's diet, as it consumes plants that may hold a lot of sand.
Manatees have only six cervical (neck) vertebrae. Most all other mammals, including giraffes, have seven. As a result, manatees cannot turn their heads sideways, they must turn their whole body around to look behind them.
The manatee's rib bones are solid, there is no marrow. They make red blood cells in their sternum where marrow is found.
The manatee has pelvic bones, but they are not attached to its skeletal frame. They are remnants of a time when manatees lived on land. The bones are found in a cartilage tissue area of the body in the vicinity of the reproductive organs and the urinary bladder. The bones are soft when the manatee is young and later harden as they mature.
Other remnant bones found in the manatee are the hyoid bones located near the neck region. These bones are similar to the Adam's apple in humans. Today, there is no known use of these bones in the manatee.
The manatee's lungs lie along its backbone instead of along its rib cage as is found in most mammals. The lungs are long (1 meter or more in adults), wide (20 cm), and thin (5 cm or less). Besides breathing, the lungs help the manatee with buoyancy control.
The bones in a manatee's flipper are similar to a human hand. The jointed "finger bones" of the flipper help the manatee move through the water, bring food to its mouth, and hold objects. Three or four nails are found at the end of each flipper.
The adult manatee averages about 10 feet long and weighs about 1000 pounds.

Additional Information:

Manatee Education

What to Do if You See a Sick, Injured, Dead, or Tagged Manatee

Image Credit: