Presence of Manatees in the Nariva Swamp noticeable by the subtlest of clues that hint at their existence in this beautiful paradise; gentle swirls at the water’s surface, a trail of bubbles along their path, the rounded tip of its nose quietly breaking the water for a breath of air or the well eaten lush vegetation. Chances of seeing these beautiful creatures, which have survived through evolutionary time, are few. The only glimpse of a manatee in the wild here is often of its nostrils.
Manatees and their relatives the dugongs are marine mammals of the biological family Sirenia, which originated in the middle of the Eocene period about 50 million years ago. Manatees are gentle, herbivores, which are often referred to as “Sea cows” because of its eating behavior. The name manatee comes from the Haitian word “manati”. The closest living relatives to manatees that still exist are elephants, hydraxes and aardvarks. Manatees are classified as sub-ungulates despite the fact that they live in water. Manatees have thick grayish tough and wrinkled skin and sparse bristle-like hairs scattered throughout their bodies and thick whiskers on their snout. They have two flippers to either side of their bodies and their tails are enlarged, paddled shaped and horizontally flattened.
Most of the manatee’s day is spent eating, resting and traveling as well as playing with other manatees. They are very agile creatures. A manatee uses its flippers and tail; to steer itself and propels its body forward through the water with the upward and downward movements of its tail. They play with other manatees by rolling, performing aquatic somersaults and body surfing. Their extra-dense bones enable them to stay suspended at or below the water’s surface.
The manatee’s diet consists of both aquatic and semi-aquatic plants. These include manatee grass, various species of algae, mangrove leaves and water hyacinths and various other plants found in their habitat. On an average a manatee consumes approximately ten percent (10%) of its body weight daily in vegetation. Their digestive system allows the bacterial breakdown of cellulose in the hindgut. Manatees have intestines up to 150 feet long, which accommodates the large volume of high fiber food which is consumed on a daily basis.
The manatee’s flipper has jointed bones. This facilitates the manatee to use its flipper similarly to how we use our hand. The manatee is able to move through the water, bring food to its mouth, and hold objects. At the end of each flipper one can find nails similar to those found on the elephant. Manatees have restricted movement of their necks. This is due to the fact that they have six cervical vertebrae as opposed to seven cervical vertebrae like most other mammals. They therefore must turn their whole bodies in order to look around.
Manatees have no front teeth, they have “marching molars”, their only kind of teeth. Throughout a manatee’s life, the molars are constantly being replaced, and adaptation to their diet of abrasive vegetation. The lower jaw of the manatee has horny pads that help it to grasp the plants. Manatees use their muscular lips to tear plants and guide food to their lips. Its upper lip is split down the middle and each side can move independently. Generally manatees feed in the water, either on the surface or at the bottom, but they are sometimes seen hauling themselves partially out of the water to feed on bank side vegetation or to crop overhanging branches.
Manatees have a large, double-nostriled snout. The upper lip is large and flexible with whiskers on its surface (vibrissae). Each vibrissa has its own separate follicular blood supply and nerve endings. Manatees can grow over 13 feet in length and weigh up to 3,500 pounds. Lengths of about 10 to 12 feet and weights of 1200 to 1500 pounds are average for adults. Despite their size manatees have little fat; they are a sub-tropical species which are very susceptible to cold. Although they have small eyes their eyesight is very good. Manatees have a membrane which can be drawn across the eyeball for protection. They have very good hearing and large ear bones, though there are no external ear structures. Manatees vocalize by a series of chirps, whistles and squeaks. The range peaks at 3 – 5 kilohertz. Communication takes most between mother and calf, or if there is danger. Manatees vocalize to express fear, anger, pain or sexual arousal. They are adapted to hear infrasound frequencies below 20 hertz. The manatee’s brain is not very convoluted, but it has an unusually high ration of grey to white matter.
Manatees will normally surface to breathe through their nostrils ever three to five minutes. When very active however they surface as often as every thirty seconds. A manatee can stay submerged for up to fifteen to twenty minutes. Manatees have a slow reproductive rate. One calf is born every three to five years. Normally it gives birth to one calf, and the occurrence of twins is rear. At birth the calf is around three to four feet long. The mother guides the calf to swim to the surface to breathe. The newborn calf weighs about sixty to seventy pounds. The female manatee has one teat located just below each flipper, on which her new born suckles. In the case of twins each calf suckles on either side of its mother. The newborn calf starts suckling, underwater, a few hours after birth.
The gestation period of the manatee is over one year, approximately thirteen months. Mothers nurse their young for long periods. The mother and baby swim together and the baby is often seen holding onto its mother’s back with its tiny flippers. The dependency of the baby lasts about two years. Communication between mother and calf is often heard by continual chirps and squeaks. The calf starts eating vegetation when it is just a few weeks old. Calves are born with molar and premolar teeth.
Female manatees are sexually mature by six to seven years and males by about nine years. An estrous female maybe pursued for weeks by several males who compete to mate with her.
There are several species and sub-species of manatees that exist. In Trinidad it is the Antillean manatees (Trichechus manatus manatus) which live in the Nariva Swamp, a freshwater habitat. We must note that manatees are migratory animals and are adapted to both salt and fresh water habitats. Manatees can live up to sixty years. Manatees do not pose any threat to any animal and have no natural predators. The only harm that is poised to the endangered manatee is man. Poaching of the manatee, pollution and the destruction of the natural habitat of the manatee are the main causes for the depletion of this highly endangered species here in Trinidad.