A blue whale can beat its heart at just twice a minute when it's diving for food

A blue whale can beat its heart just twice a minute when diving — a rate that is half as slow as had previously been thought possible — an experiment has found.

The test — the first to take the heart beat of the largest-ever animal — was achieved by attaching a non-invasive sensor to its skin at the surface using a long pole.

Four suction cups secured the sensor near the whale’s left flipper, where it recorded a heart beat through electrodes embedded in the centre of two of the suckers.

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A blue whale can beat its heart just twice a minute when diving — a rate that is half as slow as had previously been thought possible — an experiment has found

‘We had no idea that this would work and we were sceptical even when we saw the initial data,’ said lead author and biologist Jeremy Goldbogen of Stanford University.

‘With a very keen eye, Paul Ponganis — our collaborator from the Scripps Institution of Oceanography — found the first heart beats in the data.’

‘There were a lot of high fives and victory laps around the lab.’

The researchers’s analysis suggests that the blue whale’s heart is working at its limit, which may explain why the creatures have never evolved to be any bigger.

Similarly, this may help explain why the blue whale is the largest known animal of all time — because the energy needs of a larger body would outpace what a heart can sustain.

The findings shed light on the extreme ranges of heart rates in blue whales during diving, feeding and surfacing.

Professor Goldbogen and colleagues found that blue whales slow their heart rate for deep dives, but expend energy to lunge forward and engulf water for filter feeding.

Professor Goldbogen and colleagues found that blue whales slow their heart rate for deep dives, but expend energy to lunge forward and engulf water for filter feeding 

The team monitored the heart rate of a whale swimming in California’s Monterey Bay for 8.5 hours, during which it dived multiple times.

Foraging dives lasted as long as 16.5 minutes and reached a maximum depth of 184 metres (604 feet), whereas the giant mammal typically only stayed at the surface for less than four minutes.

Heart rates during dives reached a minimum of two beats per minute — well below the predicted resting heart rate of 15 beats per minute — surging to 2.5 times the minimum heart rate during lunge feeding.

During surface intervals, the heart rate reached 37 beats per minute after very deep dives — near the blue whale’s maximum heart rate — as the whale worked to re-oxygenate its tissues.

The test — the first to take the heart beat of the largest-ever animal — was achieved by attaching a non-invasive sensor to its skin at the surface using a long pole

Ten years ago, Professor Goldbogen and Mr Ponganis measured the heart rates of diving Emperor Penguins — and for had years wondered if they might do the same with whales.

‘I honestly thought it was a long shot because we had to get so many things right,’ said Professor Goldbogen.

These factors, he explained, included ‘finding a blue whale, getting the tag in just the right location on the whale, good contact with the whale’s skin and, of course, making sure the tag is working and recording data.’

The full findings of the study were published in the journal Proceedings of the National Academy of Sciences. 

WHAT DO WE KNOW ABOUT WHALE SONG?

For a long time it was believed that whales sang solely for mating purposes.

But some experts suggest the songs also help the mammals explore their surroundings.

Researchers have recorded humpback whales changing their calls when they move to new pastures in order to match the songs of others around them.

Learning these songs may help whales pinpoint one another and group together better when in unfamiliar waters.

Researchers have recorded humpback whales changing their calls when they move to new pastures in order to match the songs of others around them (file photo)

It is tricky for scientists to study how whales sing, as the shy beasts are notoriously difficult to observe, and each species vocalises differently.

Humpback whales sing using folds in the vocal box that vibrate at low frequencies as air is pushed over them.

It has been suggested they have special air sacs adjoining these vocal chords which connect to the lungs.

These allow the whales to pass air between their lungs, the sacs, and the vocal chords without losing any of their precious air supply.