Ecological Services in the Caribbean
Oficina de Servicios Ecológicos del Caribe -- Southeast Region
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Antillean Manatee Fact Sheet

Trichechus manatus manatus
Familia: Trichechidae
Orden: Sirenia

three manatee photos

Description 
The Antillean manatee (Trichechus manatus manatus) is a grey marine mammal, adults are eight to 15 feet long and weigh as little as 400 pounds and as much as 1,400 pounds. At birth, calves measure over 3 feet and weigh between 35 and 60 pounds. Sexes are distinguished by the position of the genital openings and presence or absence of mammary glands.  Females appear heavier and bulkier than males of the same length.  The manatee body is round, tapering into a spoon or paddle-shaped tail. Their body is covered with sparse hairs and their snouts with stiff whiskers called vibrissae that give it another sensory tool. Manatees have unique lips that help them gather, grasp and manipulate food and have teeth that they keep replacing as long as they live.   Because they are mammals they must come up for air.  Their nostrils are like little valves located at the tip of the snout above the mouth and can remain tightly closed when they dive under water.  Manatees can remain submerged for 15 to 20 minutes. Manatees have two front flippers with three nails on each.  Their scientific name, Trichechus manatus, means three (Tri) and chechus (nails).  

Biological Information 
The Antillean Manatee reaches adulthood at about six years of age and the oldest in captivity reached over 60 years of age.  In the wild, in Puerto Rico, studies suggest they live up to 27 years of age. Adult manatees in Puerto Rico measure between 8 and 9 feet in length. Florida manatees are larger. Females typically give birth to only one calf every three to four years after a gestation period of 13 months.  There have been a few cases of twin births. Calves are completely dependent on maternal care for survival, nursing for up to two years.

Diet:  Manatees are herbivores, feeding primarily on seagrasses and aquatic plants that grow in shallow coastal waters and rivers. The Antillean manatee feeds primarily on three seagrass species in Puerto Rico: paddle grass (Halodule wrightii), turtle grass (Thalassia testudinum), and manatee grass (Syringodium filiformis).  Occasional use of mangrove and accidental ingestion of green alga and hydroids has been reported.    

Distribution:  The Antillean manatee occurs along coastal shallow and estuarine waters of Puerto Rico and do not use the marine habitats around the islands of Mona, Monito, or Desecheo and are rarely seen around Culebra and Caja de Muertos.  Both sightings and strandings of manatees in the US Virgin Islands are extremely rare.  Aerial surveys indicate manatees are more heavily distributed along the southern coast of Puerto Rico versus the northern coast. Some “hot spots” include Ceiba, Vieques Island, Jobos Bay in Salinas and Boquerón Bay.  Manatees are least abundant along the north coast, between Rincón and Dorado and on the west along Añasco.     The Antillean Manatee is also present along the coasts of the Greater Antilles, the Gulf of Mexico, the eastern coast of Central America and further south along the north coast of South America all the way to northeastern Brazil.     

Threats 
From1980 to 2012, at least 214 manatee died in PR. The leading causes of death result from natural and human related causes.  About 37% of manatees died of natural causes, 26% die of human-related causes, and 36% of the causes are unknown mostly because bodies are found in advanced state of decomposition. 

Human causes  

  • Boat strikes:  Collisions with motorized watercrafts, boats and jets keys are the primary caused of human related deaths of manatee in Puerto Rico.    
  • Poor boatmanship: Carelessness in shallow waters can damage seagrass beds.   
  • Harassment:  Feeding, watering, or swimming with manatees or engaging in any activity that could alter manatee behavior can cause these animals to leave sheltered areas and move into areas more commonly used by humans. 
  • Habitat modification: Increases in commercial and recreational activities along the coast could affect manatee habitat.  Construction and expansion of ports and marinas could damage seagrass beds.
  • Pollution: Contaminated water and discharges make their way into the rivers polluting manatee drinking water and food sources.  Human demands for potable water will likely increase, possibly limiting sources of clean drinking water for manatees. In the future, the potential loss of fresh water sources may be the most limiting habitat factors for manatees. 

Natural Causes 

  • Hurricanes and stressful conditions: Hurricanes may cause calf to get stranded and may eventually die. In 1996, a manatee death was correlated with heavy surf produced by Hurricane Hortense and in 1998, Hurricane Georges separated a manatee cow and calf.

Conservation Measures
The West Indian Manatee was designated as an endangered species in 1970.  Manatees are protected through a number of Federal and Commonwealth laws that specify that manatees should not be given food or water, touched or followed. The primary regulations at the Federal level are the Endangered Species of Act 1973, and the Marine Mammal Protection Act of 1972.  Commonwealth laws include several regulations that provide protection for the Antillean manatee and its habitat, such as the New Wildlife Law of 1999; Regulation No. 6766 for the management of vulnerable and endangered species; the Aquatic Safety and Navigational Law of 2000; and Law No. 147 for the protection, conservation, and management of coral reefs in Puerto Rico.   

Commonwealth and federal agencies implement actions to improve habitat conditions and minimize threats to the manatee. The Caribbean Ecological Services Field Office implements a Rescue, Rehabilitation and Release Program for the Antillean manatee population in Puerto Rico.  Manatee strandings in PR are coordinated by the DNER Marine Mammal Program with collaboration from the Caribbean Stranding Network (CSN) and the Puerto Rico Zoo.   The Puerto Rico Zoo in western Puerto Rico and the Manatee Conservation Center in the Bayamón Campus of the Interamerican University in the north provide critical care and long-term rehabilitation to rescued manatees in Puerto Rico. 

Federal and Commonwealth agencies also work with developers to incorporate conservation in development project to address adverse effects to manatee habitat.  No wake areas, marked navigation channels, boat exclusion areas, and standard construction conditions for marinas and boat ramps, are but a few of the strategies used to minimize threats.   

One of the most effective manatee conservation strategies is the designation of federal Manatee Protection Areas (MPAs), where speed limit zones and/or closures can be set in some areas.  MPAs in Puerto Rico are in the planning phase and studies are underway to identify the most suitable regions of the island for the manatee.  The DNER also has a manatee conservation and protection plan that establishes boat slow speed zones within important manatee areas in Puerto Rico.   Regulatory speed buoys help boaters identify navigable waterways and speed limits to avoid or minimize collisions with manatees.

Individuals are encouraged to follow these recommendations   

  • Use polarized sunglasses while navigating. These help to detect any manatee, shallow waters and any other obstacle in the water.   

  • If you see a manatee within the path of your vessel, reduce the velocity to 5 mph and turn your vessel away from the manatee’s path or wait until the manatee has moved from the area by putting your vessel in neutral.

  • After you are certain that the manatee is well outside of the path of your vessel, resume navigation slowly (not more than 5 mph) until your vessel is not less than 50 feet (15 meters) away from the manatee.   

  • Obey regulatory speed zones and reduce velocity in shallow waters less than 10 feet, particularly close to the coast, in river mouths, in sea grass beds and mangroves. 

  • If you observe a manatee while in the water, passively observe it, do not follow it, nor harass or touch.   

  • Do not throw trash in the water. Manatees may ingest or entangle on trash, which may injure or kill it.      

  • Never feed or give water to a manatee. It is illegal and will wrongly habituate them to approach areas where they can be injured.     

  • Avoid damaging sea grass beds with anchors and propellers, and enjoy encounters with these animals from a distance.    

  • Report accident involving a manatee immediately. If you find a baby manatee alone, call the Department of Natural and Environmental Resources Law Enforcement at 787-724-5700 or the Marine Mammal Rescue Program at 787-833-2025, 787-538-4684 or 787-645-5593. 

References

  • Mignucci A. 2010. El manatí de Puerto Rico.  San Juan, Puerto Rico:  Red Caribeña de Varamientos & Universidad Interamericana de Puerto Rico, 56 pp. 

  • Mignucci-Giannoni, A.A. 1989. Zoogeography of marine mammals in Puerto Rico and the U.S. Virgin Islands. MS Thesis. Department of Marine Affairs, University of Rhode Island, Kingston, R.I. 448 pp. 

  • Mignucci-Giannoni, A.A. and C.A. Beck.  1998. The diet of the manatee (Trichechus manatus) in Puerto Rico.  Marine Mammal Science, 14(2): 394-397.  

  • UNEP. 2010. Regional Management Plan for the West Indian Manatee (Trichechus manatus) compiled by Ester Quintana-Rizzo and John Reynolds III.

  • CEP Technical Report No. 48. UNEP Caribbean Environment Programme, Kingston, Jamaica.  U.S. Fish and Wildlife Service. 2008. 5-Year Review, West Indian Manatee (Trichechus manatus). Prepared by the USFWS in cooperation with the Manatee Recovery Team. 81 pp.

Resources

Last updated: April 2, 2013
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