In waters near our shores, strange and melodic sounds can be heard during certain times of the year. It is the singing of whales that visit the island. Some of them are born here and return when they are about to give birth.
Marine mammals are not well known in Puerto Rico because they only appear occasionally and they can rarely be seen. The best known marine mammals in Puerto Rico are manatees, because they live closer to the coast and they visit river mouths. Other marine mammals in the Caribbean are whales, dolphins, and sea lions. It is feared that sea lions may have become extinct.
Unlike fish, mammals are characterized by being: warm-blooded, they breathe through lungs, have skin covered with hair, internal fertilization and development of offspring, mammary glands, and a relatively-developed brain. Marine mammals hold their breath for long periods of time by plugging their ears while they are submerged. Some of these characteristics have been modified to adapt to aquatic life. For example, their limbs have been developed for swimming and whales have little or no hair when they reach adulthood.
Many of these species are endangered. Therefore, their conservation is essential and generates greater interest in our aquatic natural resources.
The Department of Natural Resources (DNR), Caribbean Stranding Network, "Sea Grant" Program, and the Marine Sciences Department of the University of Puerto Rico, as well as other foreign organizations through a specialized staff, have focused their efforts toward research for better understanding these organisms.
Whales, dolphins, sea lions, and manatees are an integral part of our natural heritage. Therefore, they must be studied and fully protected.
The West Indian manatee, Trichechus manatus, is found from southeastern United States to the northwestern coast of Brazil. Two subspecies are identified: Florida manatees (Trichechus manatus latirostris), found in the southeast of the United States, and West Indian manatee (Trichechus manatus manatus), found in the rest of the Caribbean, including Puerto Rico.
The adult manatee can reach a length of 4.3 meters and can weigh more than 1,600 kg. Females tend to be longer and heavier than males. The color of adults ranges from gray to brown; offspring are dark-colored at birth, and their color lightens after the first month.
Manatees are primarily herbivores. They feed on a variety of submerged, floating, and emerging aquatic plants. In Puerto Rico, manatees feed mostly on marine herbs such as are thalassia and syringodium. Adults consume approximately between 8 and 11 percent of their body weight per day. Their peculiarity of being the only herbivore marine mammal gives them a major ecological niche. Manatees serve as biological agents for the control of aquatic vegetation and can influence other levels of aquatic ecosystems such as distribution, production of the plants they consume, and encouraging nutrient cycling.
Freshwater, estuarine, and marine ecosystems may serve as habitat for the West Indian manatee, which may move freely between areas of extreme changes in salinity. Manatees have no specific mating season; therefore, offspring may be born throughout the year. They have a low reproductive rate: their gestation period is about 13 months and have a single offspring every 3 to 5 years. These reproductive characteristics make this species highly vulnerable. Offspring depend on their mothers for a minimum of two years, but remain together until they are four years old, not just for food but to learn migration routes and feeding sites.
In Puerto Rico, manatees are found around the entire island, except in the islands of Desecheo and Mona. They are mostly seen from the town of Dorado to the town of Mayagüez, but especially in the area of Fajardo, Ceiba, Jobos Bay in Guayama and at the mouth of the Rio Guanajibo in Mayagüez. The manatee is considered the most endangered marine mammal in the entire area of the northeastern Caribbean. Studies conducted at the end of the 1970s and in 1984 suggest that only between 63 and 200 manatees remain in Puerto Rico. Its endangered status is directly related to human contact, as evidenced by excessive hunting of the species and deaths due to accidents with fast boats.
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