When I saw “world’s largest animal” in the title of a recent scientific study published in Proceedings of the National Academy of Sciences, I assumed it was about blue whales. I was right. J. A. Goldbogen of Stanford University and 10 colleagues measured a blue whale’s heart rate when it was swimming and diving. To study a creature in the wild that weighs twice as much as the largest land-dwelling animals ever known to have existed (Titanosaurus dinosaurs) is no small feat.
As you might imagine, measuring the heartbeat of a leviathan is a multistep process. One essential step is to find a blue whale for the experiment. Another is to locate the heart. You must then find a way to count how many times it beats each minute. To do these things, you need money. Justifying such a study to funding agencies and the scientific community is another critical point.
The study is justifiable for several reasons. First, basic research is never wasted. Finding out something previously unknown about a vital organ in a whale may lead to questions not previously considered. Learning how the circulatory system of the largest living animal functions would contribute to basic scientific knowledge. A general principle is that smaller animals have higher metabolic rates and faster heartbeats than larger ones. Determining a blue whale’s heartbeat under normal swimming and diving conditions helps anchor a baseline point for comparing heart rates among animals. The authors noted, “No heart rate profile data have been collected for any large whale at sea.”
Blue whales roam the world’s oceans from the North Pacific and Atlantic to the Antarctic, although individuals from various populations seldom mix. They occur in Monterey Bay, Calif., and the investigators located a male blue whale previously photographed for individual identification in 2003.
The heart of an adult blue whale weighs more than 600 pounds — and is large enough for a human to stand up inside of it. Where is it located in the body? Based on studies of other whales the research team knew the heart was behind the flipper on the left side.
As for the crucial step of attaching a device to measure heart rate, the scientists did what anyone would do — got in a small boat, approached the whale swimming on the surface, and used a 20-foot-long carbon fiber pole to apply a “suction cup-attached electrocardiogram (ECG)-depth recorder” equipped with surface electrodes.
Once a blue whale detects an edible food source underwater, it opens its mouth at an angle of more than 80 degrees and gulps in thousands of gallons of sea water full of plankton and tiny crustaceans known as krill. The longitudinal lines visible on the throat of a blue whale serve an essential function. They expand like a balloon as the whale takes in tons of water, up to 50,000 gallons, sometimes exceeding its own body weight.
The tongue, which weighs more than a large elephant, was pushed back into the throat and is then thrust forward, forcing water out through a network of bristles known as baleen. The water is expelled. The prey is held behind for the whale to swallow.
A blue whale can consume a half-ton of krill in one gulp and more than 1.5 million calories per day. The whale being studied foraged underwater for more than 16 minutes and dove to a depth of more than 600 feet. The ECG measurements revealed that heart rate slowed during dives to as low as two beats per minute, compared to 25 to 37 after a dive.
That the research team succeeded in bringing “the physiological laboratory to the open ocean” was a noteworthy achievement. The research findings on cardiac functions of a whale in the wild were a first of their kind. Blue whales are amazing creatures. Scientists who have found ways to study the inner workings of their enormous bodies are equally amazing.