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DUGONG MUMS SHOW THE WAY
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| Mother and baby dugong. Photo: GBRMPA |
Dugongs are either homebodies or hoons, say researchers at the Cooperative Research Centre for the Great Barrier Reef in Townsville.
And it all may depend on what they learned from their dugong mothers.
Dugongs are normally shy creatures, which spend their lives peacefully grazing the meadows of seagrass along the northern coasts of
Australian waters contain the world's largest population of dugongs, which are believed to be under threat from human activities along the coastline. The dugong research project has revealed important new aspects of dugong behaviour, which will need to be taken into account in the planning of fishing, netting and conservation zones along
“Dugongs are quite fussy eaters,” says Mr Sheppard. “When I started studying them, I shared the popular view that they were rather passive creatures which seldom moved far from the bays and estuaries where they live.
“I soon discovered how far and fast they can travel, how clever they are at finding the best seagrass meadows – and how much they may owe to their mothers,” he says.
Mr Sheppard says that using the latest GPS tracking technology, he and his team have been able to build up a detailed picture of the behaviour of a group of some two dozen dugongs from
“We have carefully captured each of 22 dugongs and strapped a GPS satellite tag to the animal's tail,” says Mr Sheppard. “The dugong simply trails the tag through the water behind it, and when it comes up for a breath of air, the tag also surfaces and transmits data to a receiving satellite. This gives us fine-scale data about the animal's movements, twenty four hours a day.”
The GPS tags are ultimately recovered by the researchers so that they can be re-used. They leave no trace on the dugongs.
Mr Sheppard says that when he started the dugong tracking project, he shared the common view that dugong herds were largely stationary, feeding at familiar seagrass meadows.
“I soon discovered that the herd could be divided into two behaviour types,” he says. “There are the homebodies, who seem content to stay around and graze in the familiar meadow.
“But there are also the hoons,” he says. “These animals will suddenly leave the herd and travel hundreds of kilometres to fresh fields of seagrass.
“What is clear is that they are moving purposefully to a remembered goal. This suggests that they have strongly developed spatial memories,” he says.
The research team believes that the reason that not all dugongs in a herd undertake these long voyages is that the knowledge of where to go is passed from mother to offspring, and not every member of the herd is even aware of the distant possibilities. This behaviour has also been observed in
Having both homebodies and hoons in a dugong population makes sense from an ecological point of view, because the seagrass meadows upon which dugongs depend are so patchy and unpredictable. Dugongs are therefore hedging their bets by staying put when the grazing is good and travelling to distant ‘remembered' fresh meadows when the food quality drops.
“This is graphically illustrated when, for example, a cyclone wipes out a seagrass meadow,” says Mr Sheppard. “Some members of the herd will immediately move to another feeding site. Others will actually by-pass a good seagrass meadow as if they are unaware of its existence. Others again will try to tough it out at the damaged meadow and – in some cases – even starve rather than move away.”
Mr Sheppard says that
“The increasing urbanisation of the coastline may be posing a real threat to the seagrass,” he says. “Runoff and urban pollution are changing the nature of coastal ecosystems, while we are recognising that seagrass itself is a major resource.
“It's essential not just for dugongs, but for the breeding of many species of fish and prawns,” he says.
This project supports
More information from:
James Sheppard, CRC Reef Research Centre,
Chloe Lucas, CRC Reef Media Liaison, 07 4729 8450, 0408 884 521
Prof. Julian Cribb, CRCA Media 0418 639 245
http://www.abc.net.au/science/scribblygum/august2004/
