10 Huge Facts About Whale Sharks

This fascinating, filter-feeding species will finally get its close-up in this summer's Finding Dory . Here are a few things you might not have known about the world's largest fish.

It’s often said that the whale shark’s maximum length  from end to end is about 45 feet, but this is a fish story. The longest verified measurements of live (or recently dead) specimens are in the 40-foot range.Â

How heavy can they get? That’s a difficult question to answer. Weighing such huge marine animals is no easy task; many scientists simply estimate instead. Still, researchers at the Okinawa Churaumi Aquarium have managed to weigh several individuals over the years. The heaviest they’ve encountered was a captured 30-footer that weighed just above 7 tons. In the wild, longer ones probably weigh a good deal more.

For years, there was much debate over how baby whale sharks come into the world. Then, in 1995, a pregnant female  was fatally harpooned near Taiwan. An autopsy revealed that her uteri (all sharks have two ) contained around 300 unborn embryos. This discovery confirmed that the species is ovoviviparous . In other words, whale sharks—like certain snakes—hatch from eggs that are stored inside their mother’s body. Afterward, the little fish exit her womb fully-formed.

Thirty or 40-foot adult whale sharks have few natural enemies. Juveniles, on the other hand, are easy pickings for predators  like blue sharks and marlins. These youngsters have every incentive to get big quick—which is exactly what they do.

Consider this: In just three years and 68 days, one newborn whale shark at Japan’s Oita Ecological Aquarium went from weighing 1.7 to 333.4 pounds. Another infant showed the astonishing growth rate  of 18 inches per year over 630 days.

But, like human babies, young whale sharks don’t keep growing at the same speed forever. Once the fish reach a certain size, scientists theorize that their growth rate slows down considerably. By then, the creatures have—again, in theory—become big enough to scare away would-be attackers.

Most sharks have 20 to 30 rows of pearly whites, but whale sharks have more than 300 rows . That means a whale shark has 3000 individual teeth, each one about the size of a match head.

All those teeth don't do very much, though. Despite their enormous size, whale sharks exclusively dine  on very small life forms like plankton, krill, fish eggs, and small fish . The sharks usually swallow their food whole. Attached to the gills is a mesh-like network of long, cartilaginous bars known as “gill rakers.” These allow water to escape, but prevent even millimeter-sized victims from doing so. Eventually, the meal is forced down our whale shark’s narrow throat and digested.

Sometimes, a whale shark will lazily swim with its mouth agape. This low-energy feeding technique allows the beast to passively  swallow any food items that might be in its path. But when it sees a dense cluster of potential targets, the shark changes tactics: The animal creates suction by rapidly opening and closing its jaws, pulling dinner into its cavernous maw. Here’s a look at this second method in action:

Generally, whale sharks—which are tropical and sub-tropical fish—are encountered from latitudes  30° N to 35° S. Within this range, they move around a lot: In three years, a single whale shark can travel 8000 miles or more. Though scientists don’t fully understand their migration habits, we know that the fish tend to gather en masse in specific places at specific times. For example, huge schools  visit exotic locales like the Galapagos Islands and Yucatan Peninsula every summer to gorge on plankton.

Covered in hard, tooth-like scales called denticles , the hide on a whale shark's back can be up to 4 inches thick . Whale sharks can toughen this skin still further by clenching the muscles that lie just beneath it. Conversely, their underbellies are relatively soft and vulnerable—so when approached by human divers, a whale shark will often turn  its belly away from them. Â

Most experts agree that whale sharks reach sexual maturity around age 30 , but their total life expectancy is unknown—and estimates are all over the map. According to some ichthyologists, the big fish probably die in their sixties. Others speculate that whale sharks can live to be 100 or even 150 years old. For the record, scientists aren’t completely sure about the great white shark’s maximum lifespan either—though they’re now known to reach age 70 or more.

In 2003 and 2004, a team led by biologist S.G. Wilson studied the long-term movements of six different whale sharks near western Australia. According to their results, the sharks mostly avoid deep plunges—in fact, the surveyed animals spent over half of their time within 100 feet of the surface.

With that said, though, whale sharks occasionally travel much, much further down. One of the Wilson team’s specimens, for instance, spent at least 12 uninterrupted hours at a depth of 3215 feet . And this wasn’t an isolated incident—tagged whale sharks off the coasts of India have been recorded hitting 2200- to 3200-foot depths as well. Why do the fish embark on such extreme dives? Nobody knows, although the answer likely has something to do with either keeping cool or gathering food.

No two whale sharks share the exact same pattern . Just behind their gills, every single one has a totally unique arrangement of pale, white spots. Today, this fun fact is helping biologists keep tabs on individual sharks—with some help from a secret weapon inspired by NASA.Â

Mapping out stars can be a daunting task. The Groth algorithm , created in 1986, is a pattern-recognition formula that enables NASA scientists to identify the countless star fields observed by instruments like the Hubble Telescope.

Decades later, one conservationist group is using a new version of this for a very different purpose. ECOCEAN is an Australian non-profit that runs the largest whale shark identification program on earth—and anybody with a camera can participate. The concept is simple. If you’ve ever filmed or photographed a wild whale shark, send  ECOCEAN a copy of your footage—along with some basic details about when and where the encounter occurred.

Then, a modified Groth algorithm is used to figure out if your fish is one of the 13,000-plus individuals on their record. If a match is pinpointed, you’ll get an email with a summary of that particular shark’s migration history.

Jason Holmberg of Portland, Oregon is ECOCEAN’s information architect. During the early 2000s, he worked with NASA astrophysicist Zaven Arzoumanian to develop this new fish-centered Groth algorithm. As Holmberg explained, their final product closely resembles the original. “We just adapted that from [identifying] white spots on a black night sky to white spots on the flank of a whale shark,” he told  National Geographic .Â

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