In a hard breakthrough, researchers at UC San Diego and Stanford have, for the first time, recorded the heart rate of a blue whale as it swam in the wild off California.
The team says that they had no idea that their test would work, and when they first saw the data, they were skeptical of it. Perusal of the data gathered eventually turned up the heart rate information the team looked for.
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. Studies like this add to our fundamental knowledge of biology and can also inform conservation efforts, they said.
"The biology of the blue whale has long fascinated physiologists because of the animal's extreme size", the study says.
To find out exactly how much a blue whale's heart rate changes during a dive, the study authors followed a group of whales they'd previously studied in Monterey Bay, California, and tagged one with a special sensor mounted on the end of a 20-foot-long pole (6 m).
The tag performed well on smaller, captive whales, but getting it near a wild blue whale's heart is a different task. For another, blue whales have accordion-like skin on their underside that expands during feeding, and one such gulp could pop the tag right off. Researchers didn't expect the heart's slowest rate to be so slow, nor did they expect the heart rate's peak to be so fast. The data he captured showed surprising extremes.
Living in the sea is the thing that enable blue whales to develop to such a colossal size conceivable, as no animal of that monstrosity might bolster itself ashore.
"When I started in the mid-1980s, there was uncertainty about whether blue whales would recover from the extreme exploitation they faced by whaling", said Calamabokidis. Taking a gander at the ECG results, the blue whales pulse bounced considerably during these scavenging thrusts, beating around over multiple times more contrasted with its slowest rate or bradycardia. The drastic slowing of their heart rate helps the whales conserve oxygen, allowing them to remain underwater for longer so that they can feed as efficiently as possible before needing to surface to breathe, the scientists said. This is as true for human landlubbers as it is for blue whales - however, given the whale's gargantuan size and proficiency at diving more than 1,000 feet (300 m) below the surface, their hearts are pushed to limits far beyond ours.
Heart rates during dives reached a minimum of two beats per minute, well below the predicted resting heart rate of 15 beats per minute, and surged to 2.5 times the minimum heart rate during lunge feeding.
This data was intriguing because the whale's highest heart rate nearly outpaced predictions while the lowest heart rate was about 30 to 50 percent lower than predicted. This remarkable piece of whale anatomy transports blood to the outer reaches of the whale's enormous body, contracting slowly to maintain blood flow during the long interval between beats.
"The heart rate data are consistent with allometric predictions based on body mass and the heart rate data confirm anatomical-biomechanical models of vascular function in such large animals".
"A lot of what we do involves new technology and a lot of it relies on new ideas, new methods and new approaches", said Cade. "We're always looking to push the boundaries of how we can learn about these animals".
Additional Stanford co-authors include graduate students Max Czapanskiy, James Fahlbusch, William Gough and Shirel Kahane-Rapport and postdoctoral fellow Matt Savoca. Goldbogen is also a member of Stanford Bio-X.
This research was funded by the Office of Naval Research, a Terman Fellowship from Stanford University and the John B. McKee Fund at Scripps Institution of Oceanography.