If you appreciate some of the greatest creatures on Earth, then it’s a discovery that will cheer your heart.

Scientists have stumbled upon a secret hideaway used by bowhead whales.

Located in an inaccessible part of the Greenland Sea, the hideaway has become a refuge for the whales, which are among the most endangered on the planet.

More than one hundred bowhead whales are thought to use the refuge, which has become a sanctuary that may help whale numbers recover from centuries of hunting.

Bowhead whales grow to 20 metres long, can weigh 75 tonnes and reputedly have the largest mouths of any animal. They used to live in four main groups around the world.

The largest, a population of an estimated 52,000 whales, lived in the Greenland and Barents Seas, around the island of Svalbard, which is part of Norway.

This is the largest abundance of bowhead whales reported from the Greenland Sea since the days of whaling in the sixteenth to seventeenth centuries

That was before 1611 when commercial whaling was initiated at Spitsbergen on Svalbard.

By 1911, commercial whaling ended. So many whales had been killed that too few remained to viably hunt any more.

Despite 100 years of protection, this population has shown no clear signs of recovery.

Just a few tens of bowhead whales are thought to survive in the region and the population is classified as Critically Endangered on the IUCN Red List.

However, over the last 20 years bowhead whales have been observed with increasing frequency in the Greenland Sea and in the coastal waters of Northeast Greenland, report scientists in the journal Polar Biology.

It isn’t yet clear if this is because there are more whales, or more people active at sea sighting them. Another complication is that it is difficult to count bowhead whales.

This discovery provides renewed hope for the Spitsbergen stock of bowhead whales

In summer, when most surveys are done, bowhead whales disperse. A recent satellite tracking of a single individual revealed that it moved between a wintering ground west of Spitsbergen and a summering ground of the East Greenland coast 700 kilometres to the south.

In previous centuries, whalers knew these movements, naming the two the Northern Whaling Ground and the Southern Whaling Ground, respectively, reports David Boertmann of the Arctic Research Centre, at Aarhus University in Denmark, in the journal.

Intriguingly however, some whales used to escape the hunters, disappearing in spring in dense pack ice floating near Northeast Greenland. The whalers couldn’t follow, and it’s not been clear since how important this region is to the whales.

Yet archaeological remains show that the Inuit people hunted bowheads along the coast in the fifteenth century.

The East Greenland coast was generally inaccessible to whaling vessels due to pack ice

Now research by David Boertmann and colleagues based at the Greenland Institute of Natural Resources, in Nuuk, Greenland and Copenhagen, Denmark, has revealed that the region is a hitherto unknown sanctuary for bowhead whales.

They made the discovery serendipitously, while conducting aerial surveys of walrus populations.

To spot walruses, observers flew in a plane over an expanse of open ocean water, surrounded by sea ice, known as a polynya.

To their surprise, they sighted a number of bowhead whales swimming in the polynya.

From the sightings, they can infer that perhaps more than 100 whales use the refuge.

“This is the largest abundance of bowhead whales reported from the Greenland Sea since the days of whaling in the sixteenth to seventeenth centuries,” the scientists say.

The sanctuary is in one of the shallowest parts of the Greenland Sea, with depths of less than 300 metres, meaning the whales can easily dive to catch their small crustacean prey.

“As the East Greenland coast was generally inaccessible to whaling vessels due to pack ice, the [polynya] may, during the whaling period, have acted as a summer refuge for bowhead whales,” write the scientists in the journal.

“Today the area certainly is of special conservation concern,” they say, and their study could be evidence that the number of bowhead whales is increasing.

“This discovery provides renewed hope for the Spitsbergen stock of bowhead whales that until now has shown only inconclusive signs of recovery despite more than 100 years of protection from whaling.”

However, they also caution that there are plans for oil exploration on the Greenland shelf of the Greenland Sea, and to ship zinc ore discovered in North Greenland.

So more research needs to be done into the bowhead whale populations to discover the likely impact of these plans on the animals.

Follow Matt Walker and BBC Earth on twitter.