Rich with fresh DNA, viruses and bacteria, whale snot is a highly sought-after treasure among Australian scientists.

Key points: The study of whale snot may help researchers understand the ebb and flow of Australia's whale population

The study of whale snot may help researchers understand the ebb and flow of Australia's whale population The use of drones to study whale health gives scientists fresh samples without harming the whales themselves

The use of drones to study whale health gives scientists fresh samples without harming the whales themselves In the past, researchers relied on whales that were either killed or beached, marine biologist Vanessa Pirotta says

Macquarie University marine biologist Vanessa Pirotta is using a water-proof drone fitted with a petri dish that can hover over the blowholes of humpback whales as they embark on their yearly cruise along Australia's east coast.

"The drone is flown through the densest part of the whale snot, collecting the sample," Dr Pirotta said.

"And then the lid shuts and the drone is flown back to the boat and we're happy scientists back on the boat."

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It sounds disgusting, but the snot is used by researchers to do health check-ups on the giant mammals — and even to identify whales that are pregnant.

"We can collect lung bacteria, which can indicate whether a lung is healthy or not. We can also collect viruses," she said.

It may also help the researchers crack one of the mysteries of Australia's whale population — why Southern right whale numbers have bounced back on the west coast but remain stubbornly low in south-eastern Australia.

The whales are coming

This will be the second season Dr Pirotta has been flying drones through whale blowhole sprays in the name of scientific research.

The advantage of using drones to study whale health is that it gives scientists fresh samples.

"In the past, to collect health information from whales we relied heavily on whales that were either killed — which is simply unethical — or from whales that had been stranded on a beach, in which case their health was either compromised or not very well at all," she said.

"So this method allows us to go into the field and collect samples from live, free-swimming whales to build a better picture and to understand their health in a much more non-invasive and safer way."

Humpback whales were decimated by whalers in the 19th and early 20th centuries. ( Supplied: Vanessa Pirotta )

The much-improved method of collecting snot samples is good timing ahead of the annual whale migration.

About 30,000 humpbacks from Antarctica will swim along Australia's coast to their breeding grounds in the warm waters of Queensland.

Captain Joel Rose, with Captain Cook whale watching cruises, has noticed more whales coming every year and said it "never gets old".

It has been a long road to recovery after humpbacks were decimated by whalers in the 19th and early 20th centuries.

It was not until the Endangered Species Act was introduced in 1973 that the whales were finally protected in Australian waters.

Whales weren't protected in Australian waters until 1973. ( Supplied: Vanessa Pirotta )

Since then, the population has rebounded from a low point of about 10,000 to almost 100,000, and it continues to grow.

Mr Rose said it has been great for tourists — with more whales being sighted earlier in the year there are more opportunities to catch a glimpse of the giant mammals.

"Due to the actions that our country and other countries have taken in the last 30 to 40 years, we're seeing a really good resurgence in numbers and we get some really good interactions with the animals," Mr Rose said.

"So it's something that [tourists will] never forget."

From sea monsters to tourism icons

Whaling was once the second largest industry in Australia after wool and it was not too long ago that humpbacks swimming past Sydney faced harpoons rather than drones.

Whale exhibitions have been popular at the Australian Museum, where there are collections of whale skeletons and artefacts that are over 150 years old.

Archives manager Vanessa Finney said there has been a clear shift in Australian attitudes towards whales.

Archives manager Vanessa Finney says whales are part of Sydney's "natural world". ( ABC News: Bindi Bryce )

"They've become more common in Sydney waters … so people have a different relationship to them — not as something that's about to disappear but something that's actually against the odds thriving."

Many of the illustrations and photographs collected by the museum reflect a time when whales were seen as magical sea monsters.

Research on whales previously relied heavily on dead or beached whales. ( Supplied: The Australian Museum )

"People understand that whales are both beautiful and somewhat mysterious," Ms Finney said.

"Whales are very much part of Sydney's natural world and also part of our culture because you can perhaps see them off the coast, but you can only get a glimpse."

Rough sailing ahead for whales

But scientists are warning that not all of Australia's whale species are thriving and there are plenty of challenges.

This season, Dr Pirotta is hoping to use the snot-collecting drone to study the endangered Southern right whale to find out why their numbers have not recovered as well as humpbacks.

There is a healthy population of Southern right whales along the West Australian coast line, but there are only around 300 left in south-eastern Australia.

The Australian Museum boasts whale skeletons and artefacts over 150 years old. ( Supplied: The Australian Museum )

Dr Pirotta said the biggest threats come from humans. Whales stick close to the coast and they have been known to wander into Sydney Harbour, colliding with boats and getting tangled in fishing gear.

Rising sea temperatures are also a problem.

"These animals feed in the waters of Antarctica, where they're now seeing a reduction in sea ice, which is the primary habitat for their food source, which is Antarctic krill," Dr Pirotta said.

