Dugong Hotspots Once widespread throughout the tropics, dugongs are becoming as Australian as meat pies (and no, they are not one of the mystery ingredients). In the late 1960s, herds of up to 500 dugongs were observed off the coast of East Africa, but they are soon likely to become extinct in this area. Populations in India, Sri Lanka, China, Okinawa, the Philippines, Gulf of Thailand, Malaysia, the Red Sea and Borneo have crashed. They are now extinct on Taiwan and the Maldives The Persian Gulf has the second-largest dugong population in the world at around 7,500. Australia is the stronghold for dugongs with a range from Shark Bay W.A. to Moreton Bay in Qld. The population of Shark Bay is thought to be stable with over 10,000 dugongs. Smaller populations exist along the W.A. coast. Large numbers of dugongs live along the NT coast and there are believed to be 20,000 in the Gulf of Carpentaria. A population of over 25,000 exists in the Torres Strait, while the Great Barrier Reef has a stable population of around 10,000. Dugongs are generally found concentrated in wide and shallow protected bays where seagrass beds are common. They are usually located at a depth of around 10 m. Dugongs have been known to travel more than 10 kilometres from the shore, descending to as far as 37 metres where deepwater seagrasses are found. Deep waters may provide a thermal refuge from cooler waters closer to the shore during winter. Shallow waters are used as sites for calving. If dugongs do not get enough to eat they may calve later and produce fewer young. Food shortages can be caused by many factors, such as a loss of habitat, decline in quality of seagrass, and a disturbance of feeding caused by human activity. Sewage, detergents, heavy metal, hypersaline water, herbicides, and other waste products all negatively affect seagrass meadows. Human activity such as mining, trawling, dredging, landreclamation, and boat propeller scarring also cause an increase in sedimentation which smothers seagrass and prevents light from reaching it. One of the dugong’s preferred species of seagrass, Halophila ovalis (paddle weed) declines rapidly due to lack of light, dying completely after 30 days. Extreme weather can destroy hundreds of square kilometres of seagrass meadows, as well as washing dugongs ashore. The recovery of seagrass meadows and the spread of seagrass into new areas, or areas where it has been destroyed, can take over a decade. Most measures for protection involve restricting activities such as trawling in areas containing seagrass meadows. There has been little action on pollutants originating from land. 27 Moreton Bay – Home of the Herds It is said that Moreton Bay is the only place in Australia where dugong still gather into herds, but they live right next to one of Australia’s busiest cities. Within this region, there are several dugong ‘hot spots’ that were visited repeatedly by large herds at high tide. The Eastern Banks region of the bay supports 80–98% of the local dugong population at any one time. Dugongs in other parts of Moreton Bay were at much lower densities than on the Eastern Banks. These seagrass ‘hot spots’ are over the whole Eastern Banks, but only specific parts of them. The western Maroom and northern Coonungai Banks make up a relatively small proportion of the total eastern banks region (13 km2 from 110.5 km2 of total seagrass beds). Dugongs are only rarely encountered over southern Amity Banks, Wanga Wallen Bank and in Rainbow Channel. These ‘hot spots’ contained especially nutritious seagrasses that dugongs prefer to eat and they may even eat it down in a way that makes it resprout with more easily digestible shoots. In that sense the dugongs ‘farm’ these hotspots. These hotspot areas are dominated by sparse Halophila spp. (H. ovalis, H. spinulosa and H. decipiens) with lesser amounts of Halodule uninervis. It has also been suggested that as their habitat declines, dugongs may simply be forced to graze smaller areas of suitable seagrass. Apart from the eastern banks seagrass area, only patchy dugong habitat remains in Moreton Bay. Relatively small seagrass areas in the southern bay are used by considerable numbers of dugongs year-round and dugongs may move between these areas and the eastern banks. The waters of Rous Channel, South Passage and nearby oceanic waters are also frequently visited by dugongs in the winter months. Threats to Moreton Bay dugongs are probably different to elsewhere and reflect the human activities in the bay. Major threats include mortality caused by boat strike and also loss of coastal habitat. Effects of Boat Strike 28 Dugong Hunting by Europeans When Europeans began settling Southeast Queensland in the 1820’s, they were quick to learn about bush medicines from local Aboriginal people. The oil from dugongs was held to possess enormous medicinal value. Dugongs were hunted and attempts were made to establish a market for it in London. However, the majority of the harvested dugong oil, hides, and bones were sold at the Brisbane markets. Dugong skin was also used in the manufacturing of leather products, the bones for cutlery holders and the meat for curing and consumption. Dugong oil, hides, bones and meat were produced at stations in Moreton, Tin Can, Wide, Hervey and Rodds Bays, and also at a small dugong factory in Cardwell. The stronghold of the industry from 1847 until 1969 was Moreton Bay, which then had vast herds. Even after heavy fishing, in late 1891 a pod of Dugongs were spotted just off Woody Point on the Redcliffe Peninsula. It is said that this pod measured approximately 8km wide by 300 metres deep. It was estimated that there were thousands of dugongs. Today this area has a population of approximately 500-1000. By 1888, the low reproductive rate of the dugong was beginning to be appreciated. Only 16 dugongs were caught in Moreton Bay in 1888, almost all were cows in calf. The unsustainability of such a harvest was recognised and ineffective controls were put in place. In 1893, large herds of dugongs entered Moreton Bay after extensive flooding (or more likely they were driven out of inshore bays to the East Banks where they could be easily seen and counted). Crisis apparently over, an annual three-month open season was declared. By 1896 dugongs were again rarely seen in Moreton Bay. From 1900 to the 1920s few were caught. Hunting was finally outlawed in 1969. Indigenous hunting of dugong still occurs in North Queensland today, allowed because of the cultural significance of the practice.