From
http://www.casa.gov.au/download/orders/Cao20/2011.pdf
...each occupant of a single engine aircraft shall wear a life jacket during flight over water when the aircraft is operated beyond gliding distance from land or water, as appropriate, suitable for an emergency landing. However, occupants need not wear life jackets when the aircraft is taking-off or landing at an aerodrome in accordance with a normal navigational procedure for departing
from or arriving at that aerodrome, and
occupants of aeroplanes need not wear life jackets during flight above 2000 feet above the water.