I found this text about manatees and felt it answered many of the questions I had since seeing some while kayacking in Florida.
Manatees come in a variety of sub-species. These include the adult West Indian, West African and Amazonian manatees. Each type varies in size, though they average about 10 ft. (3 m) in length overall. Large individuals may reach lengths of up to 13 ft. (4 m). Average adult weights are approximately 800 to 1200 lb. (363-544 kg). Larger manatees have been known to weigh up to 3500 lb. (1588 kg). Females generally being bigger than males. Amazonian manatees are the smallest of the three species. They are shorter and more slender. The longest recorded specimen measured 9.2 ft. (2.8 m). One particularly large specimen weighed 1058 lb. (480 kg). The manatee’s body shape becomes fullest inthe middle and narrows to a paddle-shape at the tail. The two small pectoral flippers on a manatee’s upper body are used for steering. A manatee swims by moving its large tail in an up-and-down motion. Not very colorful, manatees are grayish-brown. West Indian and West African manatees have three or four fingernails, similar to the toenails on an elephant’s feet, at the tips of their flippers. Amazonian manatees do not have fingernails. Built with few bodily contours to allow for easier swimming, manatees have no externally discernible neck nor any ear flaps. The actual opening to the ear canal is very small. For surface breathing, they employ two nostrils that lie on top of their heads at the end of the snout. Small eyes (about 0.8 in. or 2 cm in diameter) are located on the sides of the head. Given this overall physical description, you may wonder how anyone could have ever mistaken these creatures for mthyical sirens or mermaids.
Manatees are non-aggressive, non-territorial herbivores that spend most of their time feeding (six to eight hours per day) and resting (two to twelve hours per day). The remainder of their day is spent traveling, curiously investigating objects and socializing. The most fundamental social unit being between a female and her calf. Without hesitation, manatees will mouth, rub against and interact with other manatees. Best described as semi-social, these “sea cows” don’t shy away from company. Groups of manatees gather and disperse casually. These groups tend to be temporary and vary regarding sex, number, or age. Manatees also congregate at winter warm-water refuges. Manatees have even been observed participating in loosely organized, seemingly playful activities such as body surfing and follow-the-leader.
All sirenians (large aquatic mammals) are herbivores. They feed on a wide variety of submerged, emergent, floating, and shoreline vegetation. Manatees in Florida, for instance, feed on over 60 species of plants. These include turtle grass, manatee grass, shoal grass, mangrove leaves, various algae, water hyacinth, and water hydrilla. Manatees consume about 4% to 9% (32 to 108 lb. or 15-49 kg for an adult manatee) of their body weight in wet vegetation daily. They tend to feed at many different depths — off the bottom, in the water column and at the surface. They have even been known to crop overhanging branches, consume acorns, and haul themselves partially out of the water to eat vegetation along the shoreline. Manatees use their front flippers and large, flexible lips to manipulate potential food.Rough, ridged pads at the front of a manatee’s palate (up on the roof of the mouth)and lower jaw break vegetation into small pieces. Behind these pads, molars grind up the food and prepare it for digestion.
Manatees inhabit warm waters from Florida to Brazil — as well as Africa. They live in coastal waters, freshwater inlets, and river mouths. Warm, Floridian waters have provided wintering refuges for manatees. They also are attracted by the warm water outflow from power plants, where on occasion a manatee has gotten stuck. Although their range is quite large, manatees today exist only in a few small, isolated populations. They once were widespread in rivers and along coasts in their range, but they were hunted extensively in the 18th and 19th centuries. Coastal development has further reduced their populations. Today, there are less than 2,000 manatees remaining in the United States. All species of manatees are protected to some extent by national or local acts in every country they occupy. Federal and state laws have been passed that protect Florida manatees in the United States, for example. The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) is an international treaty developed in 1973 to regulate trade in all wildlife species. Moreover, all species of sirenians are protected by this treaty.