The most fascinating shark discoveries of the past decade

From sharks that walk to great whites that migrate incredible distances, here's why we should give these toothy fish more respect.

Wednesday, July 29, 2020,
By JoAnna Klein
Whale sharks (pictured, an animal feeding on plankton off the Yucatán Peninsula) can manipulate the flow ...

Whale sharks (pictured, an animal feeding on plankton off the Yucatán Peninsula) can manipulate the flow of water to capture their preferred food.

Photograph by Brian J. Skerry, Nat Geo Image Collection

Bamboo sharks walk. Ninja lantern sharks glow in the dark. Whale sharks can carry up to 300 babies at once—at different fetal stages and from different fathers. Zebra sharks experience “virgin birth.”

These are but a mere sampling of the decade’s most fascinating shark discoveries. Some 500 known species of these toothy fish ply our planet’s waters, ranging from bite size to bus size, and scientists are still becoming acquainted with most of them. Since 2000, when scientists discovered shark populations were collapsing around the world, research on sharks has ramped up across many fields of study, from palaeontology to neuroscience to biomechanics.

A quarter century later, one thing is clear: Sharks are not the senseless killers often portrayed in popular culture. For starters, these fish have large brains that range in relative size from species to species.

“Your brain is like a shark’s,” says Kara Yopak, a comparative neuroanatomist at the University of North Carolina Wilmington. In fact, as one of Earth’s most primitive creatures, sharks were first to evolve what she calls “the vertebrate brain blueprint,” which contains well-known structures such as olfactory bulbs, the cerebellum, and parts of the forebrain and midbrain.

“The biggest misconception is that sharks are these preprogrammed, small-brained eating machines,” Yopak says. “I’ve learned that’s not the case.”

As shark science expands, so does the urgency to protect the many species, two-thirds of which are threatened by overfishing, climate change, habitat loss, and poaching. One study suggests that if the world upped its marine protected areas by just 3 percent, it could potentially save 99 of the most imperiled sharks, many of which are top predators that help keep their ecosystems in balance. 

Here are more findings that have flipped our knowledge of sharks on its head.

Sharks travel further than ever imagined.

Researchers such as Barbara Block, a marine biologist at Stanford University, have been placing GPS tags on sharks and tracking their movements—and revealing their secret lives.

Previously, scientists thought great white sharks near California stuck close to the shore, hunting sea lions and seals. But as tracking technology advanced, allowing scientists to tag the sharks for longer periods, Block and colleagues learned that the predators travelled thousands of miles each winter to a warm patch of water in the open Pacific, where they made unexplained nighttime dives.

A great white swims off the Neptune Islands in southern Australia. Scientists once thought the predators hunted mostly close to home.

Photograph by Brian J. Skerry, Nat Geo Image Collection

Satellites had suggested this New Zealand-sized Pacific region, since dubbed the “white shark café,” was devoid of food. But they were wrong. Scientists found an area rich with shrimp, worms, big eye tuna, squid and various deep-sea creatures. Now that we know this white shark haunt is so crucial to their life cycle, conservationists are working to establish it as a UNESCO World Heritage Site.

Off the U.S. East Coast in recent years, a great white named Mary Lee has become a minor celebrity, beach-hopping among Bermuda, Florida, and the Jersey Shore and surprising scientists with her frequent jaunts. Mary Lee hasn’t appeared since 2017, but she has active accounts on Facebook and Twitter.

Other shark species are less peripatetic, undertaking epic migrations. In 2014, a great white named Lydia became the first known of her species to cross the Atlantic Ocean. And in 2017, a whale shark named Anne broke records by travelling some 12,400 miles across the Pacific Ocean in a little over two years.

Tooth-like scales help them swim.

All sharks are covered in hundreds of thousands of tiny denticles, which mysteriously regenerate when lost.

“Each one of which is like one of your own teeth, with a pulp cavity, dentine, and enamel covering,” says George Lauder, a fish biologist and roboticist at Harvard University. “The teeth in our mouth come from ancient scales that covered animals like sharks probably 400 million years ago.”

Recent advances in imaging technology, 3-D printing, and robotics have revealed how denticles help sharks swim. In laboratory experiments, Lauder found that sharkskin-like material moved faster and used less energy than smooth material.

The secret? Denticles reduce drag and increase lift and thrust. Size also matters; smaller denticles increase speed, and larger ones decrease it. On individual sharks, denticle patterns and sizes can vary.

Filter-feeders are more complex than thought.

Scientists once assumed all filter-feeding fish used their mouths like colanders: Anything too big to fit through the holes stuck; the rest went out with the water. But Erin “Misty” Paig-Tran, a functional anatomist at California State University, Fullerton, wondered how that could be true. Filter-feeding manta rays and whale sharks she studied near Cancún, Mexico, fed in the same place at the same time, but ate totally different things.

By testing 3-D models of sharks and manta filters in the lab, she unveiled how they do it. By adjusting their swimming speed and the width of their mouths or gill slits, the fish can catch their preferred food by manipulating the water flowing through their gullets. Generally, the faster the water’s speed, the smaller the food particles they ingest. 

The filter-feeding species have different strategies. Whale sharks stop and suction feed, surface and gulp, or swim with open mouths. Megamouths take huge gulps with their denticle-covered filters. Basking sharks swim with open mouths.

At least one shark species is omnivorous—and probably more.

In 2007, scientists studying the diet of bonnethead sharks found bellies full of up to 60 percent seagrass.

“Everyone sort of thought, myself included, that sharks were carnivores,” says Samantha Leigh, a postdoctoral researcher studying sharks in Paig-Tran’s lab. Sure, they may have eaten seagrass by accident, but could their bodies do anything with all that green stuff?

About a decade later, Leigh, then a graduate student at University of California Irvine, fed captive bonnethead sharks seagrass labelled with isotopic tracers—special molecules that allowed her to see where nutrients from the seagrass moved through the body. She found the fish digested about half the organic matter in the seagrass and incorporated its nutrients into their bodies.

“That is very similar to what some juvenile sea turtles digest,” she says. It’s the first omnivorous diet ever seen in a shark. How they do it remains mysterious, but Leigh says the sharks may get help from microbes in their guts—just like humans.

Sharks inspire materials and products that benefit humans.

Studying denticles has enabled Harvard’s Lauder, for instance, to create aerodynamic underwater vehicles with surfaces that more efficiently move through water. (Read how shortfin mako scales could help build better planes.)

In 2012, Lauder tested swimsuit material, purported to reduce drag like sharkskin, that 80 percent of winning swimmers at the Sydney Olympics wore. The Speedo LZR suits, now banned due to concerns over unfair advantage, boosted the swimmers’ performance by about 7 percent, he says. Swimsuit companies such as Speedo are working to design new suits to replace the LZR that are not considered “technology doping.”

Lauder’s research found the suits actually weren’t reducing drag for human swimmers. “The surface of these suits is actually nothing like real sharkskin,” Lauder notes. The real key was that the tight, full-body suits smoothed out any bumps on human skin.

California State University’s Paig-Tran says that filter-feeding sharks are inspiring designs for high-volume, energy-efficient, self-cleaning industrial filters for purposes like wastewater treatment, or even removing microplastics from water bodies.

“There’s a lot that’s happened in the past 10 years,” says Paig-Tran. “The more we learn about sharks, the more fascinating they become.”

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