The Secret Life of Whale Sharks

Scientists followed the mysterious species for two years to learn how to protect the planet’s largest fish.

(Photo: Victor Ruiz Garcia/Reuters)

Katharine Gammon has written for Nature, Wired , Discover, and Popular Science. A new mom, she lives in Santa Monica.

Think of it as Find My Phone for whale sharks, the world's largest but little-known fish. 

Researchers in Massachusetts and Saudi Arabia attached satellite tags to 57 whale sharks and spent two years tracking them at coral reefs near Al Lith, on the coast of the Red Sea. The scientists dove after the animals, which can grow to be 40 feet long, and attached tags to their fins using a sling spear. The tags transmitted information about the location and depth of the animals for as long as nine months.

The data revealed new insights into the animals' behavior, according to a study published in the journal PLOS ONE. The tags recorded that whale sharks regularly dove to at least 1,640 feet, and one even reached a depth of 4,462 feet. The tags also showed that most of the sharks stayed in the vicinity of the southern Red Sea during the course of the tracking.

The International Union for the Conservation of Nature lists the whale shark as vulnerable.

"Our limited knowledge of whale shark biology and ecology makes it difficult to know exactly how to protect them, and it makes it even harder to know exactly how worried we should be about their future," said Michael Berumen, a marine scientist at King Abdullah University of Science and Technology in Saudi Arabia and a coauthor of the study.

The researchers discovered that Al Lith was a popular congregation site for young whale sharks, with nearly equal numbers of female and male sharks present—an unusual occurrence.

"Our results clearly demonstrate the need for international cooperation to protect the population within the Red Sea," said Berumen. "Sharks afforded protection in one country may be exposed to threats in another country."

Whale sharks pose an unusual challenge to researchers because of their long-range travels and the frequent amount of time that they spend below the surface. That's why so-called aggregation sites, such as the newly discovered Al Lith whale shark meeting place, are so vital to understanding the species.

Berumen said that state-of-the-art technology still has limitations. "The satellite tags used in our study can track movements globally for nearly a year, but they are expensive and still have fairly coarse resolution in terms of spatial accuracy, so identifying potential breeding or birthing grounds is very difficult," he said.

"Whale sharks are really among the most memorable animals that anyone can encounter in the sea," he added. "We hope our work contributes toward a better global and local appreciation for these fishes, and ultimately we hope that future generations have the opportunity to experience them too."

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