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The Fascinating Dugongs

One of the most fascinating fish in the Marine Park is the Dugong. Recent research has discovered that the dugongs are long-distance swimmers and can travel hundreds of kilometres in search of sweet seagrass beds and warmer waters. They are also finding that dugongs are not used to living in the fast lane. A recent study by Mr James Shepherd, from James Cook University, used satellite-tracking devices to track the movements of seven dugongs for over two months.

Some dugongs travel extremely long distances with one large animal swimming almost 300 kilometres north from Hardy Bay to Great Keppel Island, where he stayed for just over a week, before returning to Hardy Bay.

Another headed north to Port Clinton, averaging 45 kilometres a day over eight days. Here he rested for a few weeks before moving an additional 500 kilometres north of the tagging point. Such wide-ranging patterns suggest that dugong populations are mobile and linked so it is important to realise that the dugong population in each bay is not isolated but part of a pod.

The research also discovered what appears to be a wintering ground for dugongs. They are sensitive to the cold and can be attracted by warmer waters from the tropics that flow into this area with the Eastern Australian current. Although this is a bare place, with hardly any seagrass and many sharks several dugongs revisited the area several times, swimming over 70 kilometres across the bay from seagrass beds at the heads. As temperatures started to rise at the end of the winter dugongs stopped visiting this area.

Research shows that while dugongs spend about 70% of the time about 3 metres from the surface they can range as deep as 37 metres. Dugong deaths as a result of boat strikes have been recorded in several areas of Queensland and management are concerned about the potential for boats to drive due gongs from habitats that are important to them.

Using a balloon to get a birds eye view of dugong behaviour and their response to bay traffic it was discovered that, because dugongs spend very little time, near the surface and are difficult to see from a boat they are easily struck. Most importantly, but perhaps not surprisingly, it was discovered that it is more difficult for dugongs to avoid boats that are moving fast up on the plane than boats moving slowly. Dugongs have a delayed response to boats and only move away from a boat when it is very close. Boats moving at high speed do not give dugongs enough time to move and often run over the animals, while dugongs always manage to avoid boats that are moving slowly.

Although dugongs are disturbed by day their reaction is relatively short and generally returned to their original behaviour within a few minutes of the boat passing. However, this result should not be interpreted as meaning boats and dugongs can survive together easily. It is important for new, dugongs, particularly in seagrass areas to be protected from boating at all times.