Body length 2.5-4 m, weight reaches 600 kg. The maximum recorded body length (male caught in the Red Sea ) was 5.8 m. Sexual dimorphism was expressed : males are larger than females.
A small sedentary head passes into a massive spindle-shaped body, which ends with a caudal fin located horizontally. The tail is different in shape from the tail of manatees and resembles a tail of cetaceans : its two lobes are separated by a deep notch. The forelimbs turned into flexible fins- like fins 35β45 cm long. Only the vestigial pelvic bones hidden in the muscles remained from the lower extremities. The skin is rough, up to 2-2.5 cm thick, covered with sparse single hair. The color darkens with age, becoming dull-lead or brownish; belly is lighter.
The head is small, round, with a short neck. There are no auricles. The eyes are small, deep set. The nostrils are pushed up more strongly than other sirens; equipped with valves that close under water. The muzzle looks chopped off; ends with fleshy lips hanging down. The upper lip carries stiff vibrissae and is bifurcated in the middle (stronger in young individuals); its structure helps the dugong to pluck algae . The lower lip and the distal part of the palate are covered with keratinized areas. Young dugongs have about 26 teeth: 2 incisors and 4-7 pairs of molars on the upper and lower jaw. In adults, 5-6 pairs of molars are retained. In addition, in males, the upper incisors turn into tusks protruding from the gums by 6-7 cm. In females, the upper incisors are small, sometimes they do not penetrate. The molars are cylindrical, devoid of enamel and roots.
In the skull of the dugong, the maxillary bones are greatly enlarged. Nasal bones are absent. The lower jaw is bent down. The brain box is small. The bones of the skeleton are thick and strong.
Dugongs survived only in the tropical zone of the Indian and Pacific Ocean : from the Red Sea along the eastern coast of Africa, in the Persian Gulf , off the northeastern coast of India , near the Malay Peninsula, Northern Australia and New Guinea , as well as in a number of Pacific islands. The total length of the modern range of dugongs is estimated at 140,000 km of coastline.
Currently, the largest population of dugongs (more than 10,000 individuals) lives near the Great Barrier Reef and in the Torres Strait . Large populations off the coast of Kenya and Mozambique have declined dramatically since the 1970s. Off the coast of Tanzania, the last dugong was observed on January 22, 2003, after a 70-year hiatus. A small amount of dugongs is found at Palau ( Micronesia ), at about. Okinawa (Japan) and the Johor Strait between Malaysia and Singapore .
Dugongs live in warm coastal waters, shallow bays and lagoons . Sometimes they go to the open sea; go into the estuaries and estuaries of rivers. They are kept above the depths of not more than 10β20 m. Most of the activity is feeding, associated with the alternation of tides , and not with daylight hours. Dugongs come to feed in shallow water, to coral reefs and shoals, to a depth of 1β5 m. The basis of their diet consists of aquatic plants from the families of species and water- red , as well as seaweed . Small crabs were also found in their stomachs. When feeding, 98% of the time is spent under water, where they "graze" 1-3, a maximum of 10-15 minutes, then rise to the surface for inspiration. On the bottom often "walk" on the front fins. Vegetation is torn with the help of a muscular upper lip. Before you eat a plant, the dugong usually rinses it in the water, shaking its head from side to side. Dugong consumes up to 40 kg of vegetation per day.
They are kept alone, but gather over forage places in groups of 3β6 goals. In the past, herds of dugongs up to several hundred heads were noted. They live mainly settled; some populations make daily and seasonal movements, depending on fluctuations in water level, water temperature and food availability, as well as anthropogenic pressure. According to recent data, the length of migrations, if necessary, is hundreds and thousands of kilometers [3] . The usual swimming speed is up to 10 km / h, but a frightened dugong can reach speeds of up to 18 km / h. Young dugongs swim mainly with pectoral fins, adults swim their tail.
Dugongs are usually silent. Only excited and frightened, they emit a sharp whistle. Cubs make bleating screams. Vision in dugongs is poorly developed, hearing is good. Captivity is much worse than manatees .
Reproduction
Breeding continues throughout the year, varying in peak time in different parts of the range. Dugong males fight for females using their tusks . Pregnancy presumably lasts a year. There is 1 calf in the litter, rarely 2. Delivery takes place in shallow water; a newborn with a body length of 1β1.2 m weighs 20β35 kg, is quite mobile. During the dives, the cubs cling to the motherβs back; milk is sucked upside down. Grown up young cubs gather in flocks in shallow water during the day. Males do not take part in raising offspring.
Milk feeding lasts up to 12-18 months, although as early as 3 months young dugongs begin to eat grass. Puberty occurs in 9-10 years, possibly later. Large sharks prey on young dugongs, only combed crocodiles and killer whales can pose a threat to adults [4] . Life expectancy is up to 70 years.
Dugongs are hunted for meat that resembles veal in taste, as well as for fat, skins and bones, which are used for crafts made in ivory . In some Asian cultures, body parts of dugongs are used in traditional medicine . From an animal weighing 200-300 kg receive 24-56 liters of fat. Due to predatory prey and habitat degradation, dugong has become rare or extinct over most of its range. Thus, according to estimates based on the frequency of catch by their nets, its number in the most prosperous part of the range, off the coast of Queensland , decreased from 72,000 to 4,220 heads from 1962 to 1999 [5] .
Currently, dugong fishing is prohibited by nets and they are harpooned from boats. Mining is permitted as a traditional craft of indigenous peoples. Dugong is listed in the Red Book of the International Union for Conservation of Nature with the status of β vulnerable species β [5] .
In Jules Verne βs novel β The Mysterious Island β, a dugong is mentioned - the faithful dog of the colonists Top fought with him in the lake named after Ulysses Grant - Lake Grant. In another Verne novel, β 20,000 Leagues Under the Sea, β one of the main characters, the harpooner Ned Land, preys on the dugong. Faced with the dugong and the heroes of the very first novel by J. Verne - " Five weeks in a balloon ", this time in Lake Chad .
