Cracking the mysteries of the elusive, majestic whale shark
It's the biggest shark. And it is the biggest fish in the sea. It is often found roaming in warm waters around the globe. It often has its huge mouth agape. It is in search of dinner.
It has a hulking appearance. But the whale shark has only tiny, almost useless teeth. It is sometimes so docile that entire boatloads of people can swim alongside the enigmatic, spotted beast. It's also one of the least understood animals in the oceans.
A group of scientists spent several weeks diving with whale sharks. They were in the Galapagos Islands. This was last summer and fall. They were attempting to solve some of the long-lasting mysteries. They tried some never-before-used techniques on the species in the wild. They took blood samples. They did ultrasound exams. They did this while swimming furiously beside them underwater.
Here's what's known about these massive marine animals. And here is what scientists are still trying to find out:
WHALE OR SHARK?
They are comparable in size to whales, But whale sharks are sharks. They typically grow to be bigger than a double-decker bus. They grow to 20 to 52 feet. They can weigh more than 20 tons. But they are filter feeders. The huge whale sharks are dangerous only to the plankton they chomp on. They also eat fish eggs. And they eat tiny fish.
The gentle giants aren't particularly fast when compared to other sharks. A simple wave of their tail propels them through the water. They travel faster than any human could ever swim. They have broad, flat heads. Their entire dark-blue bodies are covered in dots. The dots act as camouflage underwater.
They have been overhunted by fishermen for years. Now whale sharks are endangered. They are at risk of extinction.
Whale sharks prefer warm waters. They are often found feeding at locations around the world. These locations include Australia. It includes the Philippines. It includes Mexico. And it even include the oil fields off the coast of Qatar.
Hundreds of whale sharks gather in these areas at certain times of the year. It is mostly young males. They do this to scoop up fish eggs. It is unknown where adult females are feeding then.
The size of the ocean usually makes the shy animals hard to find. Jacques Cousteau only ever saw two in his decades of sea exploration.
TRACKING WHALE SHARKS.
Marine biologists have been tagging whale sharks in recent years. They do this to track their movements. Others are trying to answer questions about their life and reproductive cycles. Only one pregnant whale shark has ever been found. In 1995, a dead whale shark was found off the coast of Taiwan. It had 300 embryos inside. All the embryos were different stages of development.
"The million-dollar questions are where are they mating, hunting and where do their young live?" That's the question asked by Jonathan Green. He is director of the Galapagos Whale Shark Project.
An international database was launched to identify as many whale sharks as possible. They are doing this through their distinctive dot pattern. Each shark has a unique configuration of dots. The dots act like a fingerprint. More than 8,000 sharks have been logged so far. Scientists can only afford to spend a few weeks in the Galapagos each year. So they depend on photos. The photos are taken by visiting divers. They help scientist figure out what the whale sharks are up to. So far, none of the sharks spotted in the Galapagos has been seen anywhere else.
It is hard to conduct a medical exam on a free-swimming whale shark. So researchers only obtained two blood samples. These samples haven't yet been tested. The ultrasound exams were inconclusive. That's because more powerful machines are needed. Most ultrasound machines for animals are intended for abdominal walls that are 1 to 2 inches thick. But a whale shark's abdominal wall is about 8 inches thick.
"When we first started studying these large animals, nobody knew how to go about it," Green said. "Now we have better technology and more experience. We will hopefully be able to answer some of the fundamental questions soon."
Besides blood and ultrasound tests, scientists successfully tagged seven sharks. This is not a large number. But it's important since so few whale sharks are tracked. The pressure of deep water can cause tags to drop off. It can happen if the sharks dive below 6,561 feet. The animals often dive this deep. They do so when they're traveling long distances or possibly giving birth. But any migratory data the scientists collect when sharks stay at shallower depths can help build a picture of the sharks' life cycle.
Green and colleagues are planning further expeditions to the Galapagos. They plan to go later this year. They plan to continue their research. They want to gather more blood samples. And they want to do more satellite tagging.
"When you have so few data points, every single shark is important," said Robert Hueter. He is director of the Center for Shark Research at Mote Marine Laboratory. It is in Florida. He was not part of the Galapagos research. "These aren't like goldfish where you can get sample sizes of hundreds at a time."
WHY IT MATTERS.
In the last 75 years, the vast majority of whale sharks have been hunted by people for food. Their numbers are still dropping. This is according to Simon Pierce. He is chief scientist at the Marine Megafauna Foundation .
Some biologists worry climate change could hurt the sharks. It could reduce their food supply. Rising ocean temperatures could mean less plankton.
"If we do the things that are necessary to conserve the whale sharks, we'll be conserving the ocean itself," said Simon Thorrold. He works at the Woods Hole Oceanographic Institute. It is in Massachusetts.
Green heads the Galapagos project. It's more personal for him. "Even after years of diving with whale sharks, I still get goose bumps every time I see that huge blue shadow in the water. It's an incredibly emotional experience."