13 Fascinating (and Reassuring) Facts About Sharks
Updated: Oct. 02, 2018Spoiler: In real life, they rarely harm humans.
Humans kill more sharks than sharks kill people
It’s true: Sharks kill about six people per year across the globe, while humans kill between 75 and 100 million sharks. “The math on that is pretty simple,” says Nick Whitney, Ph.D, senior scientist at the Anderson Cabot Center for Ocean Life at the New England Aquarium, who first got interested in sharks as a kid in Michigan because the movie version terrified him. Now that he studies them for a living, he’s no longer afraid to swim in the ocean. “I know what lies beneath now, and in some ways, that makes me much more comfortable,” he says. “Then again, if I see a lot of bait fish close to shore and birds actively feeding on them, I know there are probably bigger fish nearby as well, and there are likely to be sharks, too.”
Only three shark species are responsible for most human bites and fatalities
Whitney says that of the more than 400 species of shark out there; bull sharks, tiger sharks, and white sharks are the most dangerous, but even with those groups, most bites are inspired more by curiosity than animosity. “If any of these three species wanted to kill a human and eat them, it would be easy to do,” he says. “The fact that the vast majority of those bitten even by these three species survive, that’s a good sign it was an investigatory bite.” Whitney has been bitten twice, but says both times he totally deserved it. “Most of the injuries I’ve sustained during shark work have come from other humans or slip-and-fall accidents on the boat.”
The U.S. sees more shark attacks than any other country, but very few fatalities
Most of the bites in the United States happen in Florida. In 2017, sharks attacked 31 people without provocation (there were other incidents, where the person who got bitten was trying to remove a shark from a fishing line or found some other way to rile it up), but none died. The last fatal attack in the United States happened in 2015, in Hawaii. Worldwide, only five people died after shark attacks in 2017: one in Australia, two in Reunion Island (an overseas department of France near Madagascar in the Indian Ocean), one in Costa Rica, and one in Cuba.
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Shark spotters make beaches safer for swimmers and sharks
Some places in Australia use overhead drones and helicopters to look for sharks near busy beaches, and in Cape Town, South Africa, human spotters put up flags on the beach and alert swimmers and surfers if a shark is spotted. “Shark Spotting has been a very successful program,” says Alison Kock, a marine biologist with South African National Parks. “Not only does it reduce the chances of sharks biting people, but it also provides essential ocean safety information.”
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Other shark-protection methods can be lethal
Some places use baited lines to catch sharks near popular beaches so they can be killed, though this culling hasn’t proved to reduce the number of human fatalities. In other places, giant nets surround swimming and surfing areas, so sharks can’t approach, but most animals caught in the nets die—including not only sharks, but also dolphins and sea turtles, some of which are threatened or protected species.
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Sharks aren’t killed only to protect humans
Kock says humans pose a far greater risk to sharks than the other way around: “They are currently being killed faster than they can reproduce.” Overfishing—particularly, the cruel practice of cutting off fins (for shark fin soup) and then releasing sharks back to the water to drown—is responsible for most of the losses, but sharks also get caught accidentally by longlines and nets meant for other fish, according to the World Wildlife Federation. Whale sharks, one of the least threatening species to humans (they eat plankton), were listed as an endangered species in 2016, when their numbers were found to have been cut in half over the past 75 years.
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Whale sharks are the biggest fish in the sea
They can grow as long as 40 feet and weigh more than 20 tonnes, which makes them about twice the size of most great white sharks. They do have teeth, but they don’t use them for eating. Instead, they feed primarily on plankton and shrimp, like filter-feeding whales; they open up their five-foot-wide mouths as they swim along and filter out all the food as it passes through their bodies. They aren’t aggressive toward humans, and many ecotourism operations promote SCUBA diving trips that allow people to swim with them.
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Sharks come in all sizes
Dwarf lantern sharks, which can fit in the palm of your hand, have been found in the Caribbean off the shore of Colombia and Venezuela, and are thought to live more than 900 feet below the surface, according to the Smithsonian Institution. They have photophores, organs that create light chemically, on their fins and bellies. The bioluminescence apparently helps camouflage them from predators looking up at them (making them blend in with the light from above the water) and attracts prey when they’re down in darker water.
Great white sharks are clever predators
“Sharks are smart,” says Kock. She points out that great white sharks show up every year to feed on a group of young Cape fur seal pups at Seal Island, off the coast of South Africa near Cape Town. “Cape fur seals are really smart and agile, and catching an experienced adult is hard work and difficult. But white sharks avoid this by targeting the naive seals each year.”
Sharks fill an important ecological niche as apex predators
Although we feel bad for the young seals, the role sharks play in picking off the weakest members of their prey group can be important. “Sharks play a key role in ocean ecosystems,” says Whitney. “Removing them may cause a domino effect that can impact other species, even down to corals and algae.” Without sharks thinning their ranks, large predatory fish can become more abundant; when they start eating more of the fish that typically graze on algae, then the algae might proliferate and out-compete the coral for sunlight.
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Great white sharks are travelers
Over the past couple of decades, researchers have been trying to figure out where white sharks go and why. Tagging programs have shown that west coast sharks travel north and south between California and Mexico and spend several months out in the middle of the Pacific, about halfway to Hawaii. East coast sharks range from Newfoundland to the Gulf of Mexico. In 2005, a great white named Nicole swam from Africa to Australia and back in nine months, for a total of more than 12,000 miles.
Some sharks can never stop swimming
It’s not true of all species, but great white, tiger, and mako sharks all need to keep moving in order to breathe. Whitney has used tags with accelerometers—”the same technology found in your Fitbit or iPhone”—to track the way sharks move underwater, and he’s found that great whites do something he hadn’t expected: they repeatedly swim from the surface down to the sea floor and then back up. “We can tell from the tags that when they’re going down, they just glide, and then when they’re going up they have to beat their tails pretty strongly to get to the surface,” he says. It might be a way of conserving energy, like when birds glide, and they might even be sleeping on the way down. “They have to swim constantly from the moment they’re born until they die, so this might be a way to take a break once in a while.”
Shark lifespans can be long
“Sharks are generally long-lived,” Kock says. “Great whites live up to 70 years, and Greenland sharks live up to 400 years!” In fact, Greenland sharks appear to be the longest-lived vertebrates on Earth. Scientists determine their ages by studying layers of eye tissue, and they estimate that these sharks might not reach sexual maturity until they’re 150 years old. That means accidental kills can severely impact the species’ long-term prospects. Other sharks are turning out to be older than researchers thought as well. Within the past ten years, they’ve started testing shark tissues for carbon radioisotopes that indicate if it was alive during the 1950s and ’60s, when nuclear testing was ongoing.
