The ocean’s biggest fish roams through the water, looking for dinner. What will he eat? Is he hungry for a giant jellyfish or an unsuspecting swimmer? Nope—this big guy has tiny, almost useless teeth. He’s a whale shark. He measures about 30 feet long. He weighs more than 20 tons—about as much as two and a half elephants. For dinner he wants nothing but tiny fish, plankton, algae, and fish eggs. To scientists, he is a puzzle. They just don’t know much about him!

Scientists spent several weeks diving with whale sharks in the Galapagos Islands last summer and fall. They tried a few tricks no one has ever used on wild whale sharks before. They took blood samples and did ultrasound exams—all while swimming beside the docile sharks underwater. You read that right. They were swimming underwater with SHARKS!

And that’s not easy—even with the friendly kind of shark. Whale sharks are slow swimmers compared to other sharks. A simple wave of the tail propels them through water. They mosey along at about three miles per hour. But for a human swimmer, that’s a sprint! Imagine a doctor examining a patient while running a race! Researchers in the Galapagos got just two blood samples from the sharks. Those samples have not yet been tested. The ultrasound exams didn’t give new info. The researchers need more powerful machines. Most ultrasound machines are made for animals with abdominal walls one to two inches thick. A whale shark’s abdominal wall measures eight inches.

Whale sharks are sharks, not whales. (Say that 10 times fast!) But they’re as big as whales. They typically grow to be bigger than a double-decker bus. It’s hard to believe something that big can be so hard to keep track of . . . until you think about the size of the ocean. Plus whale sharks are covered in dots that act as camouflage underwater.

Scientists will keep trying. They know so little about the mysterious beasts that every bit of data counts.