Researchers tracking blue whales and humpback whales in Monterey Bay, the Channel Islands, and Antarctica have recorded flexible underwater heart rates during foraging dives. Using custom suction-cup ECG tags, scientists found that heart rates spike to support sprint-like lunges for prey and then decline slowly during filtration.
Tracking Heart Rates During Deep Foraging Dives
When filter-feeding cetaceans dive into the ocean depths, their bodies undergo extreme bradycardia to conserve oxygen. For massive animals like the blue whale and the humpback whale, heart rates can plummet to just two beats per minute as they descend hundreds of meters below the surface. Despite this physiological slowdown, these animals execute sharp plunges, turns, and barrel rolls at depth to scoop up prey in what researchers describe as the largest biomechanical event on Earth
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Marine scientist Ashley Blawas led a study at Stanford University’s Hopkins Marine Station, recently published in PNAS, to understand how flexible these mammals’ heart rates really are while they expend large amounts of energy underwater. The challenge whales and other divers face is that they have to balance this oxygen-conserving dive response with the need to perform potentially oxygen-demanding exercise while underwater to capture prey,
Blawas told ScienceAlert.
Engineering Suction-Cup ECG Tags for Free-Ranging Whales
To measure these biometrics in the wild, researchers fitted nine whales—five blue whales and four humpback whales—with custom suction-cup tags in Monterey Bay, the Channel Islands in California, and the Western Antarctic Peninsula. Each tag stays attached for 12 to 36 hours before floating to the surface for data retrieval via satellite signal. The devices carry an accelerometer, gyroscope, and magnetometer to track movement, alongside an electrocardiogram to measure heart rate.
Recording an ECG from a marine mammal presents distinct technical hurdles. Successfully recording an ECG from a whale requires stable attachment of electrical points of contact to the animal, elimination of saltwater intrusion that could electrically short your measurement, and placement of the device close enough to the heart to pick up these small signals,
Blawas explained. Because thick layers of blubber prevent direct placement over the heart, engineers had to refine their tag design to capture the faint signals.
Surge Rates and Interval Recovery in Rorqual Whales
Data retrieved from the tags revealed that immediately after lunge-feeding, heart rates climb to approximately 21.9 beats per minute in blue whales and 28.2 beats per minute in humpbacks. These rates remain elevated during the post-lunge phase while the animals filter seawater, before gradually declining.
“What we found in this study, is that blue whales and humpback whales have flexible heart rates underwater during foraging that increase to support prey capture via sprint-like lunges, and decrease slowly between lunges.”
Ashley Blawas, marine scientist at Stanford University’s Hopkins Marine Station
Researchers draw a direct parallel between these aquatic mammals and land-dwelling athletes. This is similar to what we see in the heart rate patterns of humans recovering between interval sprints, where heart rate stays high even after the sprint is over and then slowly recovers,
Blawas noted, adding that rorqual whales likely rely on anaerobic energy stores during lunge sprints that are replenished by oxygenated blood between lunges.
Measuring Resting Heart Rate During Surface Logging
An unexpected milestone occurred when the team recorded data from a humpback whale that was not diving at all, but rather engaging in a surface behavior known as logging
. This restful state involves minimal movement as the animal remains at the surface for extended periods. The resulting data provided what researchers believe is the closest anyone has come to a measurement of resting heart rate in a free-ranging whale!
The resting heart rate during this logging behavior was measured at 18.5 beats per minute. While significantly lower than the human average of 60 to 100 beats per minute, it aligns closely with expectations for animals of comparable physical scale on land, such as elephants, which record resting rates around 30 beats per minute. This finding indicates that terrestrial mammals and large cetaceans share similar underlying drivers of metabolism and oxygen demand during periods of rest.
