Blue whales and humpback whales utilize flexible heart rates during underwater foraging to balance oxygen conservation with the high energy demands of prey capture, according to a study published in PNAS. Researchers led by Ashley Blawas of Stanford University’s Hopkins Marine Station found that while heart rates plummet during deep dives, they spike during “sprint-like lunges” to support intense physical exertion.
How Rorqual Whales Balance Bradycardia and High-Energy Hunting
Whales face a physiological contradiction when diving: they must conserve oxygen via extreme bradycardia—a slowing of the heart rate—while simultaneously performing “the largest biomechanical event on Earth.” This event involves sharp plunges, barrel rolls, and lunges to scoop up prey at depth.
According to the PNAS study, blue whales (Balaenoptera musculus) and humpback whales (Megaptera novaeangliae) do not maintain a static low heart rate. Instead, their heart rates are flexible. Blawas reported that heart rates increase specifically to support the energy needed for lunges and then decrease slowly as the animal recovers.
Did you know? A blue whale’s heart can slow to just two beats per minute during a deep dive to conserve oxygen—a rate that would cause a human to lose consciousness.
The Data: Heart Rate Spikes During the Lunge
To capture this data, the research team used custom suction-cup ECG tags equipped with accelerometers, gyroscopes, and magnetometers. These tags were attached to five blue whales and four humpback whales across Monterey Bay, the Channel Islands in California, and the Western Antarctic Peninsula.
The biometrics revealed a distinct pattern of cardiac activity linked to foraging behavior:
- Blue Whales: Heart rates increased to approximately 21.9 beats per minute (bpm) immediately after lunging.
- Humpback Whales: Heart rates spiked to roughly 28.2 bpm following a lunge.
Blawas noted that heart rates remain elevated during the post-lunge phase and decline gradually while the whales filter seawater. She compared this to human athletes recovering from interval sprints, suggesting rorquals likely rely on anaerobic energy stores during the lunge, which oxygenated blood then helps renew.
Establishing a Baseline for Whale Resting Heart Rates
While the study focused on foraging, the team recorded a rare instance of a humpback whale “logging”—a restful state where the animal stays at the surface with little to no movement.
The recorded resting heart rate for this humpback was 18.5 bpm. Blawas stated this is likely the closest measurement of a resting heart rate in a free-ranging whale to date. This figure aligns with the metabolic expectations for large mammals; for comparison, elephants on land have a resting heart rate of about 30 bpm.
Comparison of Resting Heart Rates
| Species | Approx. Resting Heart Rate |
|---|---|
| Humpback Whale (Logged) | 18.5 bpm |
| Elephant | 30 bpm |
| Human (Average) | 60–100 bpm |
Future Applications for Marine Conservation
The ability to measure heart rate in the wild provides a new diagnostic tool for marine biologists. Blawas indicated that changes in resting heart rate can serve as indicators of health and stress.
Future research may use this cardiac data to assess how whales respond to external stressors, including noise pollution and shifts in prey populations caused by environmental changes. Because the tags float and send satellite signals upon detachment, researchers can retrieve the data to build a more comprehensive library of cetacean metabolic responses.
Expert Insight: The technical challenge of these measurements is significant. Blubber acts as an insulator, making heart signals faint. The Stanford team had to engineer specific electrical points of contact to prevent saltwater from shorting the measurements.
Frequently Asked Questions
Why does a whale’s heart slow down when it dives?
It is an oxygen-conserving response called bradycardia, which allows the animal to stay underwater longer while searching for food.
How do researchers measure a whale’s heart rate?
Scientists use suction-cup tags containing an ECG (electrocardiogram) and movement sensors that attach to the whale’s skin when it surfaces.
Do whales run out of oxygen during a lunge?
According to the PNAS study, whales likely use anaerobic energy stores for the actual sprint of the lunge, then use oxygenated blood to recover during the filtering phase.
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