A diving animal slows its heart to make the oxygen in its blood last, and a blue whale is the extreme case of a big body with a slow pulse. The complication is how it eats. swallows a room full of water at a time and costs a great deal of power. Goldbogen and colleagues tagged a foraging whale with a heart monitor that also logged depth. What does the heart do during a lunge?
It runs at the edge in both directions. During dives as deep as one hundred and eighty-four meters the heart typically beat four to eight times a minute, and at one point twice. Back at the surface it ran twenty-five to thirty-seven, close to the estimated ceiling for an animal that size. Each feeding lunge drove the rate up roughly two and a half times above the diving minimum, then let it sag through the long glide.
A large animal has a slow heart, and a diving animal has a slower one still. during a dive stretches the blood’s oxygen over more time, which is how a whale stays down. For a blue whale both effects point the same way, toward a pulse that sounds impossible.
Then there is how it eats. Lunge feeding means accelerating into a swarm of krill with the mouth open and engulfing a volume of water comparable to the whale itself. That is a burst of very high power in the middle of a dive built around spending as little as possible.
Goldbogen and colleagues got an and depth recorder onto a foraging animal. On dives reaching one hundred and eighty-four meters and lasting up to sixteen and a half minutes, the heart typically managed four to eight beats a minute and at the lowest point two. At the surface afterwards it reached twenty-five to thirty-seven, close to the estimated maximum for a heart that size.
The lunges show up clearly inside the dives. During the powered ascent of a lunge the rate climbed to about two and a half times the diving minimum, then eased down through the long glide while the engulfed water drained through the baleen. Those swings explain the of a rorqual, wide and elastic enough to hold one beat’s worth of blood and keep it flowing until the next arrives.
wat. Two beats a minute at depth and nearly forty at the surface, with the aorta smoothing out everything in between.
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The spread between the floor and the ceiling is what sets an upper bound on body size, because a heart cannot be scaled up without the plumbing keeping pace.
How do we know?
Goldbogen and colleagues attached a suction tag carrying an electrocardiogram and a depth recorder to a foraging blue whale, and logged heart rate against dive profile.
What is still unknown
A single instrumented animal over a limited number of dives. The ceiling for surface heart rate is an estimate the measurements approach rather than a limit anybody has measured directly.
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