Small pod of pilot whales are stranded off Australia's south coast – just weeks after more than 350 became trapped in the harbour and died

A small pod of pilot whales have become stranded in Macquarie Harbour on Tasmania's rugged west coast, only weeks after a mass stranding in the same harbour left hundreds dead.

The Department of Primary Industries, Parks, Water and Environment are responding to reports a large pilot whale became stuck in the harbour near Strahan on Saturday afternoon.

Three smaller pilot whales, which were swimming with the large whale before it became stranded, also remain in the harbour.

The Department of Primary Industries, Parks, Water and Environment are responding to reports four whales have become trapped in Macquarie Harbour, on Tasmania's west coast where 470 of the mammals were stranded last month

The whales appear to be healthy and should be returned to sea on Sunday, wildlife biologist Sam Thalmann says.

'The harbour is a large, complex marine environment, with very dark waters and an intricate shoreline making detection of these whales difficult,' he said. 

'However, once the whales are stabilised, we will make all efforts today to move these whales back out to sea.'

It comes after about 470 long-finned pilot whales were found beached on sandbars at Macquarie Harbour in late September - the biggest mass stranding on record in Australia.

After a week long rescue effort, only 111 could be saved, leaving authorities the gruesome task of disposing of more than 350 carcasses.

Tasmania is the only state in the country where mass groups of whales and dolphins regularly become stranded, according to the DIPIPWE. 

Despite rescuers' best efforts, only 111 whales could be saved.  Pictured: Authorities battling to save a beached whaled on September 22

Reasons include misadventure, disorientation caused by shallow waterways or rough seas, or even flight response when in contact with a superior species. 

Long-finned pilot whales are most frequently involved in mass strandings in the island state. 

Beached whales most often die of dehydration. The animals have a very thick layer of blubber that keeps them warm in deep-sea temperatures, but causes them to rapidly overheat near the surface.

A stranded whale may also be crushed to death by their own weight, without water acting as a support, or else if they are stranded in deep water they may drown if their blowholes are covered.

Why are the whales stranded?

Tasmania is the only part of Australia prone to mass strandings, although they occasionally occur on the Australian mainland.

Scientists are unsure why exactly they run aground.

Marine Conservation Programme wildlife biologist Kris Carlyon said the pod may have been drawn into the coast to feed or by the misadventure of one or two whales, which led to the rest of the pod following.

Marine scientist Vanessa Pirotta said there were a number of potential reasons why whales might become beached, including navigational errors. 

'They do have a very strong social system, these animals are closely bonded and that's why we have seen so many in this case unfortunately in this situation,' Ms Pirotta said.

Another potential cause is when the whales use magnetic fields for navigation, they get perplexed by geomagnetic anomalies or they may be following a sick member of their group that got stranded 

Long-finned pilot whales are known for large strandings because they stick together in tight social structures.