As winter approaches in the Southern Hemisphere, humpback whales move north from their Antarctic feeding grounds to give birth in the South Pacific. The journey takes up to six months, but once they reach their destination, the region's warm waters provide a safe haven for calves. 

During a fishing trip off the coast of New Caledonia, one vessel got an unexpected glimpse of these 30-ton visitors.

We're glad to see that the captain idled the vessel during the whales' graceful show of curiosity. This sub-population of humpbacks is considered endangered by the IUCN, so boats must maintain a distance of at least 100 metres.

Located some 3,000 kilometres off Australia's east coast, New Caledonia harbours the second-largest barrier reef in the world. And thanks to dedicated conservation work over the past decade, that site now includes a marine protected area that spans an impressive 392,708 hectares.

We've long known that humpback whales make use of New Caledonia's calm lagoons, but early last year, researchers discovered something else: these migrating giants also stop over at the various underwater mountains ("seamounts") that surround the island territory. Just what they do there, however, remains something of a scientific mystery.

"Seamounts could act as a navigational cue or landmark," explain the authors. "These features often have distinct geomagnetic signatures, which may be used by species that are known to detect magnetic fields during migration."

But the whales do more than just cruise past these mid-water peaks – they actually spend time in their shadows. Experts suspect the structures provide restful shelter after the long migration, ahead of the breeding and mating rituals that follow. 

In the humpback world, attracting a mate is all about that bass. Male whales will suspend themselves nose-down in the water column to project their songs, which are among the longest and most varied in the animal kingdom. Take a look at this clip, filmed off nearby Tonga by underwater cameraman and naturalist Tony Wu:

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Top header image: Wam Wamland/Flickr