FACTS ABOUT DUGONGS
Dugongs, sometimes called sea cows, are the only herbivorous mammals that are strictly marine. They are slate grey in colour and can grow up to 3m in length and weigh up to 400kg. A flattened, broad tail fluke is moved up and down to propel them through the water and two pectoral flippers stabilise and steer the Dugong. Dugongs have a large distinctive snout and a thick layer of fat for insulation. They have relatively small eyes so their vision is quite poor, but their hearing is acute. Sexual dimorphism (differences in body characteristics between males and females) is either absent or females are slightly heavier than males.
Australia has the largest remaining population of Dugongs in the world. They inhabit warm shallow protected bays and range in a northern arc from Shark Bay in Western Australia to Moreton Bayin southeast Queensland. Globally the Dugong inhabits the Indo-Pacific region spanning over 40 countries. Across that vast range the distribution of Dugongs has contracted to relatively small and isolated populations, except for Australia. For that reason, wise conservation and management of Dugong populations in Australia is very important.
Dugongs are vegetarians that feed exclusively on sea grass. The sensitive bristles just above their mouth feel through the sand to locate the sea grass. A large adult dugong can eat up to 60kg of sea grass in one day. And it's not just any seagrass - different seagrass species have very different nutritional value for dugongs, some very good, some have not much food value at all.
Dugongs don't reach maturity until they are about 10 to 17 years old. Female Dugongs attract a small group of males who fight for the chance to mate with her. After a long gestation period of about 13.5 months the female will give birth to only one calf (very rarely twins). She will then suckle her calf for about a year and a half from external nipples just under the flippers. Female Dugongs only give birth once every 3 to 7 years. All these things combined mean that the breeding cycle of a dugong is naturally very slow, so their populations recover very slowly from a population decline that might be caused by a cyclone, or a flood and agricultural runoff.
Many factors pose a threat to Dugongs. They are typically very vulnerable to these threats due to their slow population growth rates. The seagrass that is their food source is a true plant that requires light to grow so any increased sediment in the water that affects its clarity or increased nutrient concentrations in runoff can eventually cause the sea grass to die off. Dugongs may then starve, sometimes in their hundreds. Because Dugongs are slow moving animals (reaching speeds of only 10km/h) and commonly feed in shallow water (where most of their seagrass food lives) they are often the victim of boat strikes where they are injured by collisions with speeding boats. Becoming trapped and drowning in shark nets and commercial gill nets is probably the greatest threat to dugongs who can only hold their breath for a maximum of 4 to 6 minutes.