We have checked the pulse of a wild-living blue whale for the first time, and discovered something remarkable. When blue whales dive for food they can reduce their heart rates to as low as 2 beats per minute. This is well below the rates the large animals were calculated to have. Previous predictions were that the whales would have a resting heart rate of 15 beats per minute.
The finding is particularly extraordinary given that whales have an energetically demanding feeding method, says Jeremy Goldbogen at Stanford University, California. During lunge feeding, a blue whale engulfs a volume of prey-filled water that can be larger than its own body.
From a large inflatable boat in Monterey Bay, California, Goldbogen and his team used a 6-metre pole to attach heart rate monitors to a single blue whale. The monitors were held in place with suction cups. The researchers were then able to monitor the whale’s heart rate for almost 9 hours. They detected heart rates of just 2 to 8 beats per minute hundreds of times.
The whale dived for as long as 16.5 minutes at a time, reaching a maximum depth of 184 metres, and stayed at the surface for intervals ranging from 1 to 4 minutes. The whale’s heart rate was at its lowest when it was diving for food and shot up after it resurfaced, reaching a peak of 37 beats per minute.
The reduction in heart rate during dives enables whales to temporarily redistribute oxygenated blood from the heart to other muscles needed for lunging, says Goldbogen. Whales then recover upon resurfacing by dramatically increasing their breathing and heart rate, he says.
These results demonstrate “the quite extraordinary level of flexibility and control that these diving mammals have over their heart rate and blood flow”, says Sascha Hooker at the University of St Andrews, UK.
Recent technological advances have enabled these kinds of readings to be collected from free-living whales, says Hooker. “These are opening the door to a much greater understanding of how these animals are able to perform some quite amazing feats of diving and exercise,” she says.
Journal reference: PNAS, DOI: 10.1073/pnas.1914273116
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