Blue Whale Heart Rate Can Drop to Just Two Beats Per Minute While Diving
For the first time, scientists have recorded the heart rate of a blue whale, finding it can drop to as low as two beats per minute while diving deep beneath the surface. The fastest rate recorded was 37 beats per minute at the end of very deep dives as the whale recovered and reoxygenated its enormous body.
Blue whales are the biggest animals on Earth, reaching between 80 and 100 feet in length. They are believed to have appeared about 1.5 million years ago. Earlier this year, researchers found evidence to suggest that baleen whales—which blue whales are a type of—evolved huge body sizes far earlier than once thought, raising questions about their role they have played in the development of ocean ecosystems.
Their extreme size has also fascinated scientists looking to understand their physiology—how they got to be so big and whether they could get any larger.
In a study published in PNAS, a team led by Jeremy Goldbogen, from Stanford University, report how the were able to attach a heart monitor to a blue whale in California's Monterey Bay. The male, who is known to be at least 15 years old, was followed for 8.5 hours, during which it dove down over 600 feet for up to 16.5 minutes.
The team had attached an electrocardiogram by attaching four suction cups to the whale. At the end of the monitoring period, the cups detached and the researchers collected them and started analyzing the data stored.
Findings showed that while diving, the whale's heart rate dropped to between four and eight beats per minute. At its lowest, it fell to just two beats per minute. After coming back up to the surface, the heart rate increased to 37 beats per minute—which is close to the estimated maximum heart rate of a blue whale.
While lunge feeding—a technique where the whale propels itself forward to consume prey—the lower heart rate increased by about 2.5 times, before gradually dropping back down as it glided along.
The team was surprised at their findings. The upper limit almost exceeded expectations, while the lower heart rate was about 30 to 40 percent slower than predicted. They believe blue whales must have specialized, stretchy aortic arches. This part of the heart helps push blood out to the body. In blue whales, it appears the aortic arch contracts slowly to allow for additional blood flow in between beats.
Researchers say the heart rate recordings indicate the blue whale has reached its upper body limit. Any bigger and its heart would not be able to accommodate its physical needs. "Animals that are operating at physiological extremes can help us understand biological limits to size," Goldbogen said in a statement.
"They may also be particularly susceptible to changes in their environment that could affect their food supply. Therefore, these studies may have important implications for the conservation and management of endangered species like blue whales."
