4.3.1.3.2 — Marine Mammals: Manatees and dugongs

Manatees belong to the order Sirenia (sea cows) of which there are only 4 extant species in 2 families, Trichechidae and Dugongidae. The West Indian manatee (Trichechus manatus), the West African manatee (Trichechus senegalensis), and the Amazonian manatee (Trichechus inunguis) are members of the family Trichechidae. The dugong (Dugong dugon) is the only surviving member of the family Dugongidae. Steller's sea cow (Hydrodamalis gigas) is also in the family Dugongidae and the only inhabitant of cold waters, but the species was extirpated by humans in 1768 just 27 years after its discovery in the North Pacific (Stejneger 1887). The dugong is listed in CMS Appendix II, because it is threatened in most of its huge range, which extends from Australasia into the Red Sea for the subspecies Dugong dugon hemprichii (Ehrenberg 1833). Its movements are poorly understood. The Government of Australia (1999) fitted 10 dugongs with satellite transmitters in the Great Barrier Reef Marine Park, where regular foraging trips of several hundred kilometres length were measured. When the species was more numerous, entire herds moved between Shore and seagrass meadows, where they feed mainly on the genera Halophila and Halodule. Therefore, the conservation of this species requires strict protection of ecologically sensitive seagrass meadows. This includes regulation or even banning of fisheries in these areas, because mortality due to entanglement in fishing gear is high. Other key threats include hunting and injuries by boat traffic. A careful analysis of threats and measures for threat abatement can be found within the Australian dugong conservation plan (Government of Australia 1999).

The Caribbean manatee, Trichechus manatus Linnaeus, 1758, faces similar problems throughout its range from Florida south to Brazil. Only populations between Honduras and Panama are listed in CMS Appendices I and II. This is within the range of the nominate form Trichechus manatus manatus Linnaeus, 1758, which extends much further including Mexico, Venezuela, Trinidad, Brazil and the Greater and Lesser Antilles. As the species is red-listed as "Vulnerable", CMS protection should cover the whole range of the subspecies.

As part of the Caribbean Environment Programme (CEP), a conservation plan has been developed.³² This extensive document is based on detailed studies of the species' biology and conservation status. Satellite studies have been initiated by the Belizean Manatee Project, in cooperation with the US Fish and Wildlife Service's Sirenia Project (http://www.wesave.org/manatee/).

Another sirenian species classified as "Vulnerable" by the 2000 Red List International (Hilton-Taylor 2000) is the Amazon manatee, Trichechus inunguis. It is the only exclusively freshwater sirenian, and is endemic to the Amazon basin, where it migrates in harmony with the hydrological cycle of the Amazon and its tributaries. From the flooded forest, it migrates to perennial lakes during the dry season. These migrations involve crossing of international borders, especially within the Upper Amazon region, where the species has become particularly rare. In spite of protection by national law, this once abundant species is endangered by hunting, increased boat traffic and environmental degradation (Rosas 1994).

The West African manatee, Trichechus senegalensis Link, 1795, is the least known of the sirenians. It is widely distributed in fresh water and coastal marine waters from Senegal to Angola, and migrates up river during the rainy season. Proposed hydroelectric dams in Nigeria and Gambia represent threats, and the Ivory Coast's population is fragmented due to development of waterways (Ripple 1999).

Sirenia are studied and monitored by the IUCN/SSC Sirenia Specialist Group, which regularly publishes a newsletter available online (http://pegasus.cc.ucf.edu/~smm/snews.htm). An excellent compilation of species accounts and further online information is provided by two organisations engaged in Sirenian conservation, Sirenian International, Inc. (http://www.sirenian.org).

This document should be quoted as part of the publication "Riede, K. (2001): The Global Register of Migratory Species ­ Database, GIS Maps and Threat Analysis. Münster (Landwirtschaftsverlag), 400 pp." + CD

 by Klaus Riede