Barely two kilometres offshore, we slip into the waters of the Indo-Pacific Ocean. The inky wilderness that engulfs us is disorienting; a world of no bearings and no borders that twists some 10,000 feet downwards. As sudden as a whisper breaks the stillness of night, an ogive ruptures the monochromatic blue. It swims toward us, moving with improbable grace, charging down an invisible migration highway. On its third breath, it sinks downward in a glide that disappears into the bowels of the Ombai Strait. Climbing back onto the boat, I grin. I just met the pygmy blue whale.

It’s a strange place to be, in an era where emerging research is rewriting what we thought we knew about the enigmatic blue whale, demanding that we rethink how – and if – we can protect it in time. The pygmy blue whale, Balaenoptera musculus brevicauda, is the smallest of four, or possibly even five, recognised subspecies of blue whales, the largest of which is referred to as the ‘true’ blue whale, or the Antarctic.

Meeting one in person quickly makes clear that ‘pygmy’ is a bit of a misnomer. Reaching lengths of up to 24 metres – a mere six metres shy of its Antarctic cousin – the pygmy blue whale is really quite large. Inheriting the hallmark blue whale features, an arch-shaped face, baleen plates and a mottled blue-grey wash, the pygmies can be distinguished from the other sub-species through a few, subtle traits: a bigger head and shorter tail, a darker hue, and a slightly different-shaped blowhole.

Though the early ancestors of whales evolved around 50 million years ago, the pygmy subspecies is a relative newcomer. It likely split from a group of Antarctic blues just 20,000 years ago during the last glacial maximum, when it’s thought the extreme cold drove whales northward in search of warmer waters.

Today, they are the only blue whale subspecies known to spend proportionally more time in tropical waters, embarking upon a seasonal migration that ranges from their warm equatorial breeding grounds in the Banda, Timor, and Savu Seas of Indonesia to the southern and western waters of Australia; a journey that can, in some cases, extend as far as the cooler sub-Antarctic.

Until relatively recently, the prevailing thought was that pygmy blue whales followed a straightforward migration, echoing that of most baleen whales: spending the summers fattening up in the colder, food-rich high latitudes before journeying to warmer seas to calf and breed – while fasting. But this ‘feast-or-famine’ annual cycle is steadily unravelling, with reports of baleen whale feeding in tropical waters increasing. And this holds true for the pygmy whales too.

Research now shows they do not strictly follow this paradigm, but instead, act as ‘staging’ migrants, who feed along their migration, replenishing their energy wherever possible.