Dear Hannah,

Of all the whales that live in the sea, the largest are blue whales. In fact, blue whales are the biggest known animals to have ever lived on our planet. Yep—even bigger than dinosaurs.

That’s what I found out from my friend Enrico Pirotta. He’s a researcher at Washington State University who is really curious about blue whales. Using math and science, he’s helping us learn more about blue whales and how they migrate along the Pacific Coast.

Pirotta explained that when baby blue whales are born, they are already massive. They weigh between 5 to 7 tons. They stretch about 22 feet long. They grow bigger and stronger, putting on a couple hundred pounds each day.

A mother whale nurses her calf a lot so it will quickly grow big enough to get food on its own. Blue whales take a big gulp of seawater and use baleen in their mouths as a way to filter out their food. They eat krill, a kind of plankton so small that we can barely see them.

Like you, I was curious why blue whales are so large—especially when you consider they feed on such tiny plankton. The answer is a little more complicated than you might expect.

“Nobody really knows why,” Pirotta said. “It’s a very important question. There isn’t one answer.”

But scientists do have a couple ideas, he added. Pirotta explained that the whales in the ocean today descended from ancestors that walked on land millions of years ago. As the whales adapted to life in the water, many changes took place.

Pirotta explained the ocean makes a pretty good environment for growing. There’s a lot of space and buoyancy. If you’ve ever floated in a swimming pool, you’ve likely got a sense of buoyancy. While our skeleton helps keep us upright, whales don’t rely on their skeleton as much. Because of the buoyancy, whale bodies can get bigger. They don’t have gravity pushing down on their body as much as we land animals do.

Being a large whale is also an advantage when you might not have dinner for a while. Food in the ocean can be pretty scattered. Whales can go several weeks without eating. They use their big bodies to store energy, just in case there aren’t a lot of krill around.

Another idea is that the large size, along with a layer of thick blubber insulation, help the whale stay warm in the water. Typically, large animals tend to lose body heat slower than small animals.

And of course, being the biggest animal in the ocean can also help ward off potential predators. It turns out being a giant in the deep serves a whale pretty well.

Dr. Universe

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