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The Biggest Mystery in the Sea
Shark!The passengers on the boat stare wide-eyed into the clear water. A huge, dark shape glides just under the surface, jaws stretched in a massive grin. The shark is bigger than a person, bigger than an elephant, bigger than the boat! Its enormous mouth is wide enough to swallow you whole.
But don’t worry! This is a gentle giant.
An Ancient Mystery Whale sharks are an ancient life form, evolved many millions of years ago, long before humans appeared, and they’re still here today. They’re the biggest fish in the world, but they eat the smallest things in the sea.
Whale sharks are among the most mysterious creatures in the ocean. In spite of the fact that they’re so laid-back that divers canget close enough to touch them, scientists know surprisingly little about them. We’re just beginning to explore the many mysteries of the whale shark.
One reason why whale sharks are so mysterious is that they’re always on the move. Endlessly crisscrossing the great oceans, they roam the deep waters of the globe. Three-quarters of the whale sharks of the world live in the Pacific Ocean, while the rest live in the Atlantic. Scientists haven’t yet figured out if these two populations ever meet each other and have young. Whale sharks mostly stay in warm tropical waters near the equator, but they sometimes come into regions of cooler waters to search for food.
Whale sharks wander through the ocean, often traveling thousands of miles in a year. Sometimes they swim far down into the shadowy depths of the sea, in waters more than a mile deep. Sometimes they come right up near the shore in shallow water, giving human swimmers a scary surprise!
Big Mouth, Small Food Although its mouth is hugely wide, the whale shark’s throat is very small—not much bigger around than a baseball. No big fish can fit down that narrow tube. Whale sharks avoid sucking in fish that are larger than your little finger. And most of their prey is even smaller.
It’s amazing to think of something the size of a school bus feeding on teeny minnows and sardines. But whale sharks’ favorite food is something so small that you can barely see it. Plankton is the name scientists give to many different species of tiny plants and shrimp-like animals that float in the open waters of the ocean. One speck of plankton is so small you need a microscope to see it, and a million of these tiny organisms could fit in a teaspoon. A whale shark can swallow millions of them in a single gulp, but it takes a
lot of plankton to fuel the body of a whale shark.
This means they have to spend a lot of time eating!
Whale sharks constantly have to seek out food. They often feed on fish eggs, and they’ll travel far across the ocean to places where fish are spawning (laying eggs). Since many marine predators hunt for fish eggs, some kinds of fish reproduce by broadcast spawning. This means that a group of fish gather and release eggs into the water all at one time. A single female tuna can release more than two million eggs at once! With billions of eggs floating around, there’s a greater chance that more will survive.
So hungry whale sharks gather where clouds of fish eggs fill the water. But to get to these rich feeding grounds, the whale sharks often have to travel a long way.
World Travelers As far as we know, whale sharks can’t swim very fast. They’ve never been clocked moving at high speeds, and usually they amble along at about two miles per hour or so—that’s as fast as the average person can swim, and Olympic athletes can swim three times that fast. When migrating, a whale shark can only average about thirty or forty miles a day. How far can they get, moving so slowly? For many years, marine biologists (scientists who study ocean life) assumed that whale sharks probably didn’t migrate vast distances.
In 2011, marine biologist Dr. Héctor Guzmán from the Smithsonian Tropical Research Institute, based in Panama, wanted to find out how far whale sharks could travel. He tagged several adult whale sharks by attaching a small device to their fins that would transmit a global positioning signal (GPS) that could be picked up by satellites—kind of like giving the whale shark a cell phone. Using these signals, his team of researchers tracked the journey of a female whale shark they named Anne.
Anne was tagged near Panama, but she soon headed west toward the Galápagos Islands. She slowly kept on for several days, and then suddenly the signal vanished. Anne had dived deep into the ocean. The satellite tag could only transmit in shallow water, so the scientists lost track of Anne for months.
Then, after 235 days of silence, the signal returned. Anne had resurfaced. And she had traveled more than seven thousand miles through deep, cold water, all the way to Hawaii. But she wasn’t done with her travels yet. The researchers followed her over the course of a year as she eventually made it close to the Philippines, completely across the Pacific Ocean. It was the longest whale shark migration ever tracked, more than 12,500 miles one way.
Scientists now think that whale sharks travel all over the oceans of the globe. But why do they put so much energy into traveling so far? Is it the need for food that drives them, or are they searching for mates? Is it a quest for a safe place to have babies? No one knows why whale sharks swim such huge distances. Do all of them travel as much as this, or was Anne an unusual wanderer? And just how deep into the shadowy depths of the ocean do they dive? There’s so much to learn about these mysterious creatures.
Copyright © 2022 by Chelsea Clinton. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
