Watching Whale Sharks
By Heidi Poelman
1 Imagine that you are swimming in the ocean and come upon a shark as long as a school bus. Pretty scary, right?
2 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. 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 wide open, filtering some of the ocean's smallest creatures out of the water.
3 Scientists have learned a lot about whale shark, but much of the animals' lives is a mystery.
Filling Up on Little Bits
4 The shark makes an entire meal out of tiny prey. 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 of its gills. In the process, it eats about six pounds of plankton and small fish....
5 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?...
How to Track a Shark
6 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 sharks 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.
7 Tracking tag 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
8 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.
9 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 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."
10 No one know 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 Yucatan 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.
11 For now, scientists keep searching for answers. As Dr. Hueter puts it, "The more we learn about whale sharks' travel and their favorite hangouts, the better we can understand and conserve them."
