A blue whale’s heart can beat as few as two times a minute.
The discovery comes from data collected during researchers’ first few attempts to measure the heart rate of the world’s largest animal, and the results, published Monday (November 25) in PNAS, reveal how the whales survive their deep dives to find food.
Recording the whale’s heartbeat was not an easy feat. It required attaching electrodes sitting atop suction cups to the behemoth’s body at exactly the right spot—just behind the left flipper. “To be honest, I thought it wasn’t going to work,” study coauthor Jeremy Goldbogen, a zoologist at Stanford University, tells The Atlantic.
Much to Goldbogen’s surprise, the tactic did work. Maneuvering in a small, inflatable boat, he and his team sidled up to a blue whale that had surfaced in California’s Monterey Bay and used a 20-foot pole to tap the sensor onto the whale’s skin. After it was tagged, the whale went down for a foraging dive, and a few hours later, the sensor floated to the water’s surface. The team retrieved it and took it back to the lab.
Downloading and analyzing the sensor data, the team found that the whale—a 72-foot-long male—had a heart rate of only a few beats per minute, sometimes as low as two, when it dove, and then, when it surfaced, the whale’s heart rate skyrocketed to as high as 37 beats per minute. The dynamic tempo is what surprised the scientists most: models of resting heart rate based on size had suggested that the whale’s should be somewhere around 11 beats a minute, and so the team expected there would be some period when its heart rate would hit this speed. But it didn’t. It vacillated between the fast rate and the slow one.
That extreme vacillation shows “the quite extraordinary level of flexibility and control that these diving mammals have over their heart rate and blood flow,” Sascha Hooker, a physiologist at the University of St. Andrews who studies diving mammals and was not involved in the study, tells New Scientist. The technological advances that allowed this type of data collection, she notes, 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.”
Goldbogen tells Reuters that “in particular, new measures of vital rates and physiological rates help us understand how animals work at the upper extreme of body mass.” It helps scientists answer questions such as, “What is life like and what is the pace of life at such a large scale?”
Ashley Yeager is an associate editor at The Scientist. Email her at firstname.lastname@example.org.