ABU DHABI // A sudden dip in recorded deaths among the emirate's threatened dugong population has sparked hope the gentle marine creature may be recovering from intensive building work along the coastline. Conservationists have long warned that the dredging, land reclamation and increased boat traffic associated with a boom in the development of marinas and hotels was taking a devastating toll on the rare mammals.
But after two years of record numbers of dugong deaths, scientists at Environment Agency-Abu Dhabi (EAD) have noticed a drop in the rate. In 2007, there were 12 deaths recorded, but so far this year the number is only six, said Dr Thabit Zahran al Abdessalam, director of marine biodiversity management sector at EAD. There were 11 deaths of recorded during 2006. Dugongs are listed as a species vulnerable to extinction by the International Union for Conservation of Nature, which has updated its "Red List" of threatened plants and animals.
The lugubrious creatures grow to between two and three metres in length, can weigh of up to 400 kg and live up to 70 years. Their skin is deep grey and they have a flat, two-pointed tail that propels them through the water. Instead of front limbs, they have flippers that they use to steer. They are herbivores and their diet consists mainly of seagrass. Their ability to eat the equivalent of 15 per cent of their body weight has gained them their other name: the sea cow.
Although protected by federal law, they have faced growing threats from coastal development, seismic activity by the oil industry and oil pollution. The number of recorded deaths is relatively small and the reduction only recent, but Mr Abdessalam is hopeful a trend has emerged. Two reasons could explain the reduction. "My perception is that the extent of land reclamation was much greater in 2006 and 2007 and also mitigation measures had not been implemented then," he said.
Land reclamation usually involves dredging, an operation which disturbs the seabed as sand, rocks or clay are removed. This changes the physical and chemical composition of the water, which can in turn threaten the health of coral reefs and seagrass beds, which are very sensitive to such changes. Dredging increases the murkiness of water, making it harder for seagrass, the dugong's principal source of food, to grow. Dredging also stirs up a lot of nutrients in the water which encourage algae. If these organisms multiply too quickly, they can use up all the oxygen in sea water, killing large numbers of fish.
One way of reducing the problem is to use sediment curtains, vast swathes of material that surround the dredging area and contain the murkiness by filtering the water. Increased boat traffic linked to the building activity is another problem. Mr Abdessalam said that a number of dugong died after being hit by boats. The only way to stop this was to ask boat owners to avoid dugong-dense areas and observe speed limits. "We have been trying to implement these measures since 2006," he said.
Seismic surveys carried out during oil exploration can also have devastating effects. Mr Abdessalam described how scientists had found a dead dugong with signs from bleeding from its nose and ears: "That means that there was some kind of acoustic disturbance." Seismic surveys explore the geology beneath the seabed by releasing low-frequency pulses that work in the same way as sonar or radar devices. The pulse penetrates the layers beneath the seabed and its echo is recorded and analysed as it bounces back. While these sounds might not disturb humans, they bother dugongs and other marine animals, which can hear sounds in the lower range of the spectrum.
