Amanda Hodgson

Sirenian social and reproductive behaviors lack much complexity or diversity. Whereas sirenians are usually sighted as solitary, or as cows with single calves, aggregations of many individuals can occur. Persistent social groupings are unknown. Home ranges are widely overlapping. Mating systems of dugongs (Dugong dugon) have been variously described as leks or as scramble promiscuity (mating herds ) and lone mating pairs have been observed in areas of low density, but further research into the hypothesized leks is needed (especially because scramble promiscuity has been observed in the same region). Dugongs and all manatees (Trichechus) show scramble promiscuity, wherein males form groups that escort single females with much physical contact for many days. The strongest social bonds are between females and nursing calves. Florida manatees (Trichechus manatus latirostris) show natal philopatry for years after weaning. Socially transmitted knowledge (tradition) appears important to Florida manatees and perhaps all species of sirenians, particularly in regions where seasonal movements during winter are necessary for survival, such as in winter for Florida manatees, and dugongs at the high latitude limits of their range. Some populations of Antillean, Amazonian, and African manatees have regular movements in response to seasonal flooding and access to food, which also may be learned through tradition . Dugongs may rely on group movements based on traditional knowledge in response to regional loss of food supply from extreme weather events. Communication is most obvious through vocalizations, which can show individual distinctiveness. Vocal communication is most prevalent between mothers and calves. Allomaternal care occurs in Florida manatees at shared aggregation sites. Florida manatees occupying a given region can consist of multiple matrilines that develop through the early bonding of calves to mothers and subsequent natal philopatry. Population genetics research supports male-biased dispersal and possible female-based philopatry in other trichechids, but perhaps not as strongly in dugongids. Considerable further research is needed on these and related topics to more comprehensively understand sirenian social and reproductive behavior.

Manatees and dugongs live in tropical and semi-tropical regions around the world. Their preferred habitats are seagrass beds, rivers, lakes, and estuaries. Manatees live in both freshwater and marine systems although habitat preferences vary across the three species, while the dugong is entirely marine. Sirenians are shallow water divers, and their dive durations are short compared to most other marine mammals. The maximum recorded manatee dive duration is 24 min, with the maximum recorded duration of a dugong dive being about half that. Even though the durations of dugong dives are shorter than those of manatees, current data indicate that dugongs dive deeper than manatees. Dive depths for manatees generally do not exceed 5 m, other than during occasional travel over deeper water; however, this may be an artifact of water depth in areas where diving data were recorded, or where manatees live. In some parts of their range, dugongs are found over deep-water seagrass beds and dives have been recorded to more than 30 m. All extant sirenians eat diverse plant-based diets: collectively they have been documented feeding on at least 55 genera of marine and freshwater plants. Although not confirmed for the Amazonian manatee, it is likely that all extant sirenians eat animal, as well as plant, matter. West Indian and African manatees have been documented eating marine and freshwater fish and invertebrates , and for African manatees, these food resources are a regular part of their diet, arguably making them omnivores . Dugongs have been recorded targeting invertebrates at the high latitude limits of their range in winter. All manatees like to drink fresh water, in contrast to dugongs, which live entirely in marine systems and apparently meet the water requirements from their food.

The role of sirenians in aquatic ecosystems is largely a function of their feeding ecology. Sirenians are large herbivorous aquatic mammals that often congregate and, being mammals, have high energetic requirements relative to other marine herbivores. An adult dugong can weigh from 250 to 600 kg¹, while the West Indian and West African manatees both range between 350 and 1,400kg², and the Amazonian manatee from 200 to 480kg³. Consequently, sirenians consume significant amounts of aquatic vegetation. They also display dietary preferences in regard to plant species, individual plants, and parts of plants4,5. Thus dugongs and manatees have the capacity to...

In the Arabian region dugongs occur in the Red Sea and the Arabian (Persian) Gulf (map 10.1). They are known locally by a variety of names: bugarah al bahr (cow of the sea: Bahrain, Qatar, and UAE); arus al bahr (bride of the sea: Gulf and central Red Sea coasts of Saudi Arabia, and Bahrain); taweelah (southern Red Sea coasts of Saudi Arabia and Yemen); al jild (skin or leather: at Wejh in Saudi Arabia and Hurgadhr in Egypt); and naqat al bahr (camel of the sea: northern Red Sea).