Blue whale: breaking all the rules

It may be bigger than a dinosaur, but the amount we don’t know about the blue whale is probably larger still. Now, new research suggests this giant may be more numerous than we’d dared hope.

 

Blue whale, Balenoptera musculus, California, Pacific Ocean

A blue whale underwater in California © Mark Conlin/Getty

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It’s a tense moment. We peer into the deep water surrounding our boat. “Pffffffffff.” The whale ruptures the surface like a submarine, clearing the water from its huge blowholes and showering us with fishy brine.

There’s no question what we’re looking at. It’s hard to mistake a blue whale – it is three times as long as our boat, with tail flukes the width of soccer goalposts. The issue our team from the Oman Whale and Dolphin Research Group (OWDRG) can’t agree on is what the whale is doing here, in the Arabian Sea, in February – a month when it should be feeding in the Southern Ocean.

Encountering a blue whale is a humbling experience, because these creatures are incredibly rare. Whalers wiped out 95 per cent of the world’s population before hunting was outlawed in 1967, and it’s thought that fewer than 10,000 now remain. The Southern Hemisphere (which, in terms of blue whale populations, encompasses the Arabian Sea), suffered most, and what we wanted to know was how many were left here.

Needle in a haystack

Studying blue whales isn’t easy – the OWDRG has experienced just seven sightings in nine years. But a good place to start is near their food source.

Despite their size, blue whales feed exclusively on krill – tiny, shrimp-like crustaceans – and must consume four tonnes of them each day. Scientists thought that, to find such vast quantities, blue whales conducted bi-annual migrations from their winter breeding grounds in the tropics to summer feeding grounds at the Poles.

However, research is showing that this may not be the case. In January 1998, an IWC research team sighted more than 60 blue whales in the Chilean fjordlands, and it’s since been proved that they remain there all year.

But why? “These waters are very productive,” says Dr Rodrigo Hucke-Gaete, of the Universidad Austral de Chile. “Why bother leaving if you can feed and breed in one place?”

The Chilean blues are not the only ones rewriting the rulebook. The Arabian Sea population may also be staying put all year, taking advantage of the region’s rich food resources. What’s more, blue whales are also known to feed in nutrient-rich gullies off the west coast of Australia. In fact, there are now so many exceptions to the rule that blue whales migrate that it may never have been a rule at all.

“Satellite images indicate that blue whales inhabit waters rich in chlorophyll,” says Trevor Branch, who presented his findings at last year’s IWC conference. “Some blue whales do feed in the Antarctic, but other populations may stay close to their winter food sources all year.”

Time for a recount?

This is good news. If not all Southern Hemisphere whales travel south, the current population statistics could be serious underestimates, since the only counts for southern blues are based on summer sightings below 60˚S.

But what of the whales that don’t make it down that far? And what’s going on in little-studied chlorophyll-rich waters, such as off the coasts of Pakistan and Polynesia? There are still questions to be answered.

Whatever we can learn will make a difference. If we can prove that populations here and in Chile are year-round residents, we can help protect them from illegal whaling. We can also work to understand the threats facing the species globally, such as collision with boats, entanglement in nets, dwindling food resources caused by overfishing and the effects of climate change.

But to truly protect these magnificent creatures we need to work together. Custodianship of the oceans is a responsibility held by all nations. Let’s hope we can rise to the challenge.    

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To find out more about blue whales, click here