The Florida Manatee (Trichechus manatus latirostrus).

Manatees with Man - Crystal River

The presence of the Florida manatee in local waters affords a good opportunity to reflect upon the relationship between nature and man in the context of the Crystal River manatee population.

Pachydermos (παχυδερμος in ancient Greek) means thick skin as applied to mammals like the elephant, the manatee, and rhinoceros. Florida's manatee is a marine mammal related to the elephant. It is sometimes referred to as a “sea-cow” presumably because it is observed to feed on sea grasses.

Like us, the manatee breathes air, has teeth to eat with, gives birth to and suckles it's young with mother's milk, and has hair on it's skin, whiskers on it's face and internal organs performing similar functions to our own. Unlike us, gestation takes about a year instead of our nine months, and a calf born to a manatee weighs between sixty and seventy pounds, is some forty inches long and nurses under water. Like us, there is no specific mating season. The average adult manatee is about ten feet long and weighs between 800 and 1,200 pounds - quite different to ourselves. Moreover, two large manatees were observed to enter a local spring area. Later they were seen to have been joined by a small calf. Could confirm the anecdote that some manatee births are attended by another adult female said to act as a midwife?

Whiskers and hair

Researchers look for gas bubbles when trying to locate manatees in dark waters. Being herbivores gas bubbles may be observed because of their vegetarian diet.

Both fresh and salt water suit the manatee. Salt is filtered from blood in the kidneys which also control water balance.

Suckling teats, one on each side behind a flipper, have no storage sac for milk so young suckle often and for short periods. Although young swim from birth and surface to breathe, they suckle from and depend upon their mother for up to two years.

Females may conceive young as early as four to five years of age but may not become successful mothers until they are between six to ten years old. Male manatees can procreate at seven years of age but must compete with older males vying for the attention of a female in estrus. Several males will form a mating herd and must wait for the female to decide when the time is right before mating occurs.

Anatomy.

Our skeleton enables us to move on land and use tools. The manatee skeleton is built for swimming offering a frame supporting a streamlined body ending in a flat tail or fluke. Up and down motions of its body and fluke propel the manatee powerfully as do whales, dolphins and other mammals (and as we do when using a butterfly stroke), but differently from the side to side motions of fish. Generally manatees choose to move gently and slowly in search of food, or when traveling with young calves. Normally manatees travel at about three to five miles per hour although, however, when stressed or evading, short bursts up to 20 miles per hour can be achieved.

Manatee crawls using flippers		Mother nurtures calf

Small hip bones, remnants of hind limbs, are attachment sites for muscles. However, two fore limbs (flippers) have similar bones to our own with an upper arm (humerus), elbow (olacranon), fore arm (radius and ulna) and five jointed 'fingers' ending with nails. Unlike us, only three or four of the nails protrude from the thick skin of the flipper which encases the fore limb bones. Flippers have many uses to the manatee; helping it to propel (crawl) and steer through shallower or obstructed waters, and like us, helping to bring food into its mouth, or touching, holding onto other manatees or things..

Breathing.

Manatee surfaces to breathe		Manatee swimming upside down

Like us, manatees use lungs to breathe in air to supply oxygen via the heart to energize the muscles and regulate body temperature. Unlike us, manatee lungs are flatter, and extend almost the length of the body. Air in the lungs increases buoyancy. Manatees relocate the buoyancy within their bodies to assist pitch and roll attitudes in diving or maneuvering in the water (like alligators reportedly also do) and to maintain a horizontal posture or to swim or sleep on their backs.

Unlike other diving mammals manatee muscles have little capacity to store oxygen which limits their ability to dive deeply or stay down for extended periods. Breathing takes place at the surface through two nostrils which close when submersed. When resting submerged they surface to breathe on average every three to five minutes, when using a lot of energy the norm would be once every 30 seconds. Periods of twenty minutes submerged have been timed for resting manatees.

Intelligence.

Manatee swimming

Manatees possess a relatively small brain for their size but can be taught to choose an action for reward.

Far example, in tests to determine the hearing frequencies of manatees, an arrangement of a light stimulus accompanied by a sound emission of a known frequency was used. The manatee were rewarded with food, when pressing one of two buttons the manatee correctly responded to the sound. No reward was given when the manatee responded to the light without an accompanying sound. Repetition revealed the range of frequencies actually heard. However, in subsequent tests with lower frequencies the manatee responded to sound below the frequency threshold. It was thought that variations in pressure from emitted sound upon body hair was recognized instead of actually hearing the emitted sound. Was this, like us, cheating for reward?