Commonlit | Watching Whale Sharks

Name: Class:

Watching Whale Sharks The ocean’s biggest fish is a mystery. By Heidi Poelman 2016

Scientists’ knowledge about the largest fish in the ocean, the whale shark, is limited. In this information text, Heidi Poelman discusses how scientists are learning more about this large creature. As you read, take notes on why it is difficult for scientists to study whale sharks.

[1] Imagine that you are swimming in the ocean and come upon a shark as long as a school bus. Pretty scary, right?

Well, if it were a whale shark, you would be in luck. The whale shark is the largest fish in the ocean, but it isn’t aggressive.1 In fact, its 300 rows of teeth are too small to hurt humans. When a whale shark eats, it doesn’t rip or tear. It drifts or swims with its mouth open wide, filtering some of the ocean’s smallest creatures out of the water.

"The whale shark makes a big meal out of tiny prey." by Reinhard Scientists have learned a lot about whale sharks, Dirscherl/Alamy is used with permission. but much of the animals’ lives is a mystery.

Filling Up on Little Bits

The shark makes an entire meal out of tiny prey.2 To do it, the fish filters a lot of water. In a recent study, scientists learned that in one hour a midsize whale shark can pass more than 157,895 gallons — enough to fill 13 tanker trucks — through the filters in its throat and out its gills. In the process, it eats about six pounds of plankton and small fish.

[5] Whale sharks have been found off the coasts of Mexico, Australia, the Philippines, Madagascar, and other tropical locations. They can live 75 years or more and grow longer than 45 feet. Their mouths are wide enough to hold a sofa.

That’s some of what scientists know. They have to answer many more questions to help whale sharks survive in the changing oceans. Where do the fish go when they disappear for weeks at a time? Why do they dive so deep? Where do they breed and mate?

1. Aggressive (adjective): ready or likely to attack 2. Prey (noun): the animal that is hunted and killed by another for food 1 Because the sharks swim for thousands of miles across the open sea, they are hard to study. Since 2003, one group of American and Mexican scientists has been studying whale sharks off the Yucatán Peninsula in Mexico. The scientists have put ID tags on about 750 of the giant fish and electronic tracking tags on more than 40 others.

How to Track a Shark

An electronic tracking tag allows scientists to trace a whale shark’s journey through the ocean. Scientists use a small pole spear to attach the tag to the shark’s dorsal fin. No one knows if the shark can feel the point of the spear. “Ninety-nine percent of the time, the shark shows no response,” says Dr. Robert Hueter at Mote Marine Laboratory in Florida. He’s a leader of the research group.

Tracking tags contain devices that keep a record of where each shark travels, how deep it swims, and any changes in water temperature. When the shark surfaces, the tag sends the information to a satellite in orbit around Earth. The satellite transmits the information back to Earth. “We basically get e- mails of the data,” says Dr. Hueter. “It gives a record of what the animal has been doing.”

Deep Divers

[10] Using a tracking tag, Dr. Hueter recorded a whale shark that dived to a depth of 6,325 feet, or about 1.2 miles — the world record for whale sharks so far.

No one knows why the sharks dive so deep. The reason may be because sharks don’t have swim bladders like most other fish. A swim bladder is a gas-filled sac that lets a fish rise, sink, or stay at one depth. Without a swim bladder, sharks sink toward the ocean floor to rest. This tendency to sink adds to the whale shark mystery. “If a whale shark dies in the ocean, it sinks,” explains Dr. Hueter. “So it’s very difficult to learn what happened to it.”

No one knows where whale sharks breed or give birth. In 2007, Dr. Hueter tagged what he believes was a pregnant whale shark. Over the next 150 days, the shark traveled nearly 5,000 miles from the Yucatán Peninsula to a point about halfway between South America and Africa. Dr. Hueter thinks this may be one place where whale sharks go to give birth, but he’ll need more data to find out.

For now, scientists keep searching for answers. As Dr. Hueter puts it, “The more we learn about whale sharks’ travels and their favorite hangouts, the better we can understand and conserve3 them.”

3. Conserve (verb): to protect from harm or destruction 2 Text-Dependent Questions

Directions: For the following questions, choose the best answer or respond in complete sentences.

1. PART A: Which statement best identifies the central idea of the text? A. Some of the practices that scientists use to track and study whale sharks have been considered cruel. B. Whale sharks are at risk of becoming extinct due to humans’ overhunting of their primary food source. C. Whale sharks will likely remain a mystery to scientists because of how deep they live in the ocean. D. Learning more about whale sharks is an important step for scientists to further protect them.

2. PART B: Which detail from the text best supports the answer to Part A? A. “It drifts or swims with its mouth open wide, filtering some of the ocean’s smallest creatures out of the water.” (Paragraph 2) B. “That’s some of what scientists know. They have to answer many more questions to help whale sharks survive in the changing oceans.” (Paragraph 6) C. “Scientists use a small pole spear to attach the tag to the shark’s dorsal fin. No one knows if the shark can feel the point of the spear.” (Paragraph 8) D. “‘If a whale shark dies in the ocean, it sinks,’ explains Dr. Hueter. ‘So it’s very difficult to learn what happened to it.’” (Paragraph 11)

3. Which of the following describes the structure of the section “How to Track a Shark” (Paragraphs 8-9)? A. It describes the different ways scientists' track sharks, and then why they prefer to us an electronic tag. B. It describes the benefits of using an electronic tag to track sharks, and then some of the shortcomings of the technology. C. It describes what an electronic tag is, and the information it provides scientists about whale sharks. D. It describes what an electronic tag is, and then the difficult process of attaching it to a whale shark.

4. Which of the following describes ocean’s temperatures and whale sharks? A. Rising ocean temperatures are forcing whale sharks to live deeper in the ocean. B. Cooling ocean temperatures are forcing whale sharks to leave their habitat. C. Changing water temperatures are putting whale sharks at risk. D. Changing water temperature are killing whale sharks’ food source.

3 5. What is the relationship between whale sharks’ movements and why scientists know so little about them?

4 Discussion Questions

Directions: Brainstorm your answers to the following questions in the space provided. Be prepared to share your original ideas in a class discussion.

1. How do scientists observe whale sharks and what do they know about these creatures because of their observations? Why do you think it’s important for scientists to study animals?

2. In the text, the author talks about how the temperature of the ocean is changing. How are humans in part responsible for this change? How do humans both help and harm the environment? What could you do to help the environment?

3. How do scientists use technology to learn more about whale sharks? Do you think there are any disadvantages to scientists using technology to track animals? If so, what?