12 Facts About Great White Sharks

iStock
iStock

In 1974, Peter Benchley released Jaws, a horror novel that sold 20 million copies, spawned an iconic film—and catapulted the great white shark (Carcharodon carcharias) to infamy. Although the book brought him fame and fortune, Benchley came to rethink its negative portrayal of great whites: The author-turned-conservationist said in 1995 that if he was writing his book then, “The shark … could not be the villain; it would have to be written as the victim.” The great white is now classified as a vulnerable species. Read on to find out why the truth about Carcharodon carcharias is often stranger—and always more compelling—than the fiction that obscures it.

1. EYE-ROLLING IS A DEFENSE MECHANISM.

Many sharks protect their eyeballs with a pair of clear lid structures called nictitating membranes, which act like protective, transparent eyelids. But not great whites—they don't have the membranes. Instead, their eyeballs roll backwards into the skull reflexively when a shark bites into a thrashing victim [PDF]. This exposes the sclerotic coat, a fibrous tissue that surrounds the eye.

2. SOME REPORTS ON THEIR SIZE ARE KIND OF FISHY.

The great white is a huge fish, no question—but some claims about its maximum size are probably exaggerated. In 1870, one zoologist measured the disembodied jaws of a large adult and estimated that the whole shark must have been 36.5 feet long. But a modern reevaluation—in which the jaws were compared to those from other dead sharks—showed that the creature’s actual length was probably about 16.5 feet, and the reports of the giant shark were likely a printer’s error.

And then there's the Cojímar specimen, a great white captured and killed near Cuba in the early 1940s. Those who saw it in person said the fish was 21 feet long and weighed 7100 pounds. Since then, the claim has been disputed by fish experts who, using an available photo, calculated that the animal’s real length was also in the ballpark of 16 feet. According to biologist Jose Castro’s book The Sharks of North America, the largest great white “believed to have been measured reliably” stretched 19.6 feet long. When it comes to weight, big males have been measured weighing up to 2819 pounds while the largest female weighed 4343 pounds.

3. GREAT WHITES ARE CLOSELY RELATED TO MAKOS.

According to a 2016 paper, there are 509 species of shark divided into nine orders and 34 families. Great whites belong to the lamnidae family, which contains only four other species: the porbeagle, the salmon shark, the longfin mako, and the shortfin mako. All five sharks have conical snouts, eyes that look solid black, and lengthy gill openings. They share a couple of other things as well—including a method for trapping body heat.

4. THEY CAN STAY WARM IN FRIGID WATER.

Most shark species have no direct control over their body temperatures; they're about as hot or cold as the water they’re swimming in. But there are a handful of species—the entire lamnidae family included—that are endothermic, meaning they can consistently maintain high body temperatures even in cold water.

The great white and its relatives have their powerful muscles to thank for this talent. The muscles naturally produce heat as they contract, warming up blood in that area, which is then redistributed to other parts of the body. This allows great whites to keep their core body temperature as high as 25 degrees (Fahrenheit) warmer than the ambient water, which means they can thrive in bitterly cold places. And when muscles are kept warm, they work more efficiently, so great whites can swim faster and farther than many other sharks. On the flip side, great whites need to consume a huge amount of calories in order to keep their body temperatures up.

5. NOT ALL GREAT WHITES GO AFTER THE SAME FOODS.

Great whites have varied diets and not all individuals share the same food preferences. But in general, younger sharks mostly eat fish and squids while older, larger sharks tend to go after big targets like marine mammals. Catching small fish and biting into fatty seals are, of course, two very different tasks. This explains why juvenile white sharks have narrower teeth than adults do—the better to pierce the skins of slippery fish. Living sharks of every species possess multiple tooth rows and are constantly replacing old chompers with brand new ones. As a great white matures, its incoming teeth become broader, serrated, and triangle-shaped, allowing great white adults to tear large chunks of meat off their victims.

6. GREAT WHITES CAN GET AIRBORNE.

Fatty, calorie-rich pinnipeds like seals and sea lions are common prey for large great whites, which typically attack from below in an explosive burst. The top speed of a great white is over 20 miles per hour, and during seal hunts, they can burst completely out of the water—a feat known as breaching—which leads to the successful capture of a pinniped 40 to 55 percent of the time, depending on lighting and other variables.

7. THEY DINE ON THE WORLD’S BIGGEST FISH.

In the 1960s, a 14.7-foot great white shark was captured near an Australian whaling station and, when it was dissected, two mysterious bones were found in its stomach. They were later identified as vertebrae belonging to an adult whale shark that was estimated to be 28 feet long. These filter feeders can grow to be 40 feet long and weigh at least 7 tons; experts now think that great whites are scavenging on floating whale shark carcasses rather than hunting the fish.

8. ATTEMPTS TO PUT THEM IN CAPTIVITY HAVEN’T GONE WELL.

Certain sharks thrive in aquariums; great whites don’t. Every single great white that’s been placed in captivity has either died or been released after a brief stay. The Okinawa Aquarium, Sea World San Diego, and the now-defunct Marineland of the Pacific are among the facilities which experimented with captive white sharks at some point or other. At the Monterey Bay Aquarium, one specimen spent a record-breaking six months living in a million-gallon tank. Once she began stalking other display fish, however, she was set free. Several different factors make great whites ill-suited for captivity. To breathe, the animals must be in constant motion to push water over their gills, and aquariums don’t always offer enough space for this. Other issues include the species’ famously large appetite and its tendency to run into glass walls.

9. DESPITE MYTHS TO THE CONTRARY, GREAT WHITES CAN GET CANCER.

There’s a myth that great whites and other sharks are immune to cancer, which has had some unfortunate real-world consequences. Assertions that shark cartilage is an edible cancer cure has led to mass harvesting of the vulnerable fish.

For the record, clinical tests have shown that ingesting shark cartilage in no way treats any form of cancer. Cancer has been documented in more than 20 shark species, including the great white: The first reported instance of a tumor-plagued great white was announced in 2015.

10. THEY TRAVEL VAST DISTANCES.

The great white inhabits many of the world's oceans, but they're most often found in waters with surface temperatures from 59°F to 72°F. The species also migrates seasonally. Some travel from South Africa to Australia and back every year. Other great whites cross the Atlantic, making long treks between Cape Cod, Massachusetts and the Azores, 2300 miles away. And each winter, scores of them leave Californian waters for a point researchers have nicknamed “the white shark café.” Located halfway between Hawaii and Mexico, this region doesn’t appear to offer much in the way of food, but the sharks remain there from April to July. Data from tagged great whites tells us that the males go on rapid, deep dives multiple times per day while hanging out in this area. Nobody knows why the white shark café is such a hot destination—but it might be a place where the fish gather to breed.

11. ORCAS PREY ON THEM.

When great whites get knocked upside-down, they freeze up and exhibit “tonic immobility,” a state of semi-consciousness. There’s at least one animal that can exploit the vulnerability. On October 4, 1997, an orca was seen barreling towards a great white shark (which measured 9 to 13 feet long) near one of California’s Farallon Islands. A human onlooker filmed the orca dragging the stunned fish around on its backside. Eventually, it let go [PDF], and then ate the dead shark's liver.

Between May and the end of June 2017, the bodies of four white sharks—all missing their livers—washed onto South African beaches. All four deaths have been attributed to orcas. A great white’s liver is high in fat and loaded with nutrients, which may account for the orcas’ interest in singling it out for consumption. One of the sharks had its testicles and stomach missing as well.

12. DO THEY REALLY MISTAKE PEOPLE FOR SEALS? PERHAPS NOT.

Though shark-on-human attacks are rare, most of the time, when you do hear about an attack, a great white is behind it. Since 1580, Carcharodon carcharias has been positively identified in at least 314 unprovoked attacks on humans (80 of them fatal). No other shark species is credited with even half as many.

According to one common explanation, great whites attack humans because they mistake them for pinnipeds. The argument goes that, when viewed from below, a person on a surf board projects a seal-like silhouette.

While this is a popular idea, it leaves some critical things unexplained. First of all, great whites have proportionally large eyes by shark standards—and acute vision to boot. Also, the big fish strike seals with tremendous force at great speed; by comparison, the sharks usually move at a slow, deliberate pace when approaching people. And in the vast majority of attack incidents, a great white will deliver a single bite and then leave without consuming the victim. In fact, nearly three out of every four humans who get bitten by white sharks survive the encounter.

Biologists have proposed that when the animals bite people, they do so out of curiosity (at least, in most cases). “Great whites are curious and investigative animals. That’s what most people don’t understand,” marine biologist R. Aidan Martin told National Geographic. “When great whites bite something unfamiliar to them, whether a person or a crab pot, they’re looking for tactile evidence about what it is.”

The sharks often go out of their way to nibble on inanimate objects—such as underwater cameras—before losing interest and moving on. So maybe, when they decide to bite people, they're not looking for a snack.

10 Juicy Facts About Leeches

Ian Cook
Ian Cook

Leeches get a bad rap, but they’re actually pretty cool once you get to know them—and we're finding out more about them, even today. Recently, a team led by Anna Phillips, curator of parasitic worms at the Smithsonian National Museum of Natural History, discovered a new species of medicinal leech (pictured above) in a Maryland swamp. We asked parasite expert and curator at the American Museum of Natural History Mark E. Siddall to share some surprising facts about the worms we love to hate. 

1. Not all leeches suck blood.

Hematophagous, or blood-feeding, species are only one type of leech. “The vast majority of species are [hematophagous],” Siddall tells Mental Floss, “but it depends on the environment. In North America, there are probably more freshwater leeches that don’t feed on blood than there are blood-feeders.” And even among the hematophagous species, there are not too many who are after you. “Very few of them are interested in feeding on human blood,” Siddall says. “Certainly they’ll do it, if they’re given the opportunity, but they’re not what they’re spending most of their time feeding on.” 

2. Leeches are everywhere.

Japanese leech on a log
Pieria, Wikimedia Commons // Public Domain

“Every continent on the planet has leeches, with the exception of Antarctica,” Siddall says. “And even then there are marine leeches in Antarctic waters.” Humans have co-existed with leeches for so long, according to Siddall, that just about every language has a word for leech. 

3. Leeches have made a comeback in medicine.

Bloodletting for bloodletting’s sake has fallen out of favor with Western physicians, but that doesn’t mean medicinal leeches are enjoying a cushy retirement. Today, surgeons keep them on hand in the operating room and use them as mini-vacuums to clean up blood. “That is a perfectly sensible use of leeches,” Siddall says. Other uses, though, are less sensible: “The more naturopathic application of leeches in order to get rid of bad blood or to cure, I don’t know, whatever happens to ail you, is complete hooey,” he says. How on Earth would leeches take away bad blood and leave good blood? It’s silly.” 

4. Novelist Amy Tan has her own species of leeches.

Land-based leeches made an appearance in Tan’s 2005 book Saving Fish from Drowning, a fact that instantly put the author in leech researchers’ good graces. “There are not a lot of novels out there with terrestrial leeches in them,” Siddall says. So when he and his colleagues identified a new species of tiny terrestrial leeches, they gave the leech Tan’s name. The author loved it. “I am thrilled to be immortalized as Chtonobdella tanae,” Tan said in a press statement. “I am now planning my trip to Queensland, Australia, where I hope to take leisurely walks through the jungle, accompanied by a dozen or so of my namesake feeding on my ankles.”

5. Leeches can get pretty big.

The giant Amazon leech (Haementeria ghilianii) can grow up to 18 inches and live up to 20 years. And yes, this one’s a blood-feeder. Like all hematophagous species, H. ghilianii sticks its proboscis (which can be up to 6 inches long) into a host, drinks its fill, and falls off. Scientists thought the species was extinct until a zoologist found two specimens in the 1970s, one of whom he named Grandma Moses. We are not making this up.

6. Leeches make good bait.

Many walleye anglers swear by leeches. “A leech on any presentation moves more than other types of live bait," pro fisher Jerry Hein told Fishing League Worldwide. "I grew up fishing them, and I think they're the most effective live bait around no matter where you go." There’s an entire leech industry to provide fishers with their bait. One year, weather conditions kept the leeches from showing up in their typical habitats, which prevented their collection and sale. Speaking to CBS news, one tackle shop owner called the absence of leeches “the worst nightmare in the bait industry.”

7. Leech scientists use themselves as bait.

Siddall and his colleagues collect and study wild leeches. That means hours of trekking through leech territory, looking for specimens. “Whether we’re wandering in water or traipsing through a bamboo forest,” Siddall says, “we are relying on the fact that leeches are attracted to us.” Do the leeches feed on them? “Oh my god, yes. We try to get them before they feed on us … but sometimes, obviously, you can’t help it.”

8. Leech sex is mesmerizing.

Like many worms, leeches are all hermaphroditic. The specifics of mating vary by species, but most twine themselves together and trade sperm packets. (The two leeches in the video above are both named Norbert.)

9. Some leech species make surprisingly caring parents. 

“There’s a whole family of leeches that, when they lay their eggs, will cover them with their own bodies,” Siddall says. “They’ll lay the eggs, cover them with their bodies, and fan the eggs to prevent fungus or bacteria from getting on them, and then when the eggs hatch, they will attach to the parent. They’re not feeding on the parent, just hanging on, and then when the parent leech goes to its next blood meal it’s carrying its offspring to its next blood meal. That’s pretty profound parental care, especially for invertebrates.”

10. You might be the next to discover a new leech species. 

Despite living side-by-side with leeches for thousands of years, we’ve still got a lot to learn about them. Scientists are aware of about 700 different species, but they know there are many more out there. “I’ll tell you what I wish for,” Siddall says. “If you ever get fed on by a leech, rather than tearing off and burning it and throwing it in the trash, maybe observe it and see if you can see any color patterns. Understand that there’s a real possibility that it could be a new species. So watch them, let them finish. They’re not gonna take much blood. And who knows? It could be scientifically useful.”

Fish Tube: How the 'Salmon Cannon' Works and Why It's Important

PerfectStills/iStock via Getty Images
PerfectStills/iStock via Getty Images

If you’ve been on the internet at any point in the past week, you’ve certainly come across footage of wildlife conservationists stuffing salmon into a giant plastic tube and shuttling them over obstacles. It’s so bizarre—even by the already loose standards of the web—that it briefly ignited discussions over fish welfare, its purpose, and the seeming desire of people to be similarly transported through a pneumatic tunnel into a new life.

Naturally, the “salmon cannon” has a mission beyond amusing the internet. The system was created by Whooshh Innovations, a company that essentially adopted the same kind of transportation system featuring pressurized tubing that's used in banking. Initially, the system was intended to transport fruit over long distances without bruising. At some point, engineers figured they could do the same for fish.

The fish payload is secured at the entrance of the tube—acceptable species can weigh up to 34 pounds—and moves through a smooth, soft plastic tube that conforms to their body shape. Air pressure behind them keeps them moving. The fish are jettisoned between 16 and 26 feet per second to a new location, where they emerge relatively unscathed. Because there’s no need for a water column, the tubing can cover most terrain at virtually any height.

The tubing solution is a human answer to a human problem: dams. With fish largely confined to still bodies of water thanks to dams and facing obstacles swimming upstream to migrate and spawn, fish need some kind of assistance. In the past, “fish ladders” have helped fish move upstream by providing ascending steps they can flop on, but not all fish can navigate such terrain. Another system, trapping and hauling fish like cargo, results in disoriented fish who can even forget how to swim. The Whooshh system, which has been in used in Washington state for at least five years, allows for expedient fish export with an injury rate as little as 3 percent, although study results have varied.

The video features manual insertion of the fish. In the wild, Whooshh counts on fish making semi-voluntary entries into the tubing. Once they swim into an enclosure, they’re curious enough about the tube to go inside.

If all goes well, the system could help salmon be reintroduced to the Upper Columbia River in Washington, where the population has been depleted by dams. Testing of the device there is awaiting approval from the U.S. Army Corps of Engineers.

[h/t Popular Mechanics]

SECTIONS

arrow
LIVE SMARTER