iStock
iStock

11 Facts About Bull Sharks

iStock
iStock

Compared to sharks like the hammerhead (with its oddly shaped skull) and the goblin (with its projectile mouth), the bull shark (Carcharhinus leucas) looks rather generic—but this predator can swim thousands of miles upriver, hunt baby hippos, and take over the occasional golf course.

1. BULL SHARKS HAVE A VERY STRONG BITE.

In 2012, scientists compared the bite strengths of 13 different sharks and shark-like fish and found that an adult bull shark can theoretically close its jaws with just under 6000 newtons of force at the back of its mouth and over 2000 newtons at the front. (Humans chomp with a maximum force of around 900 to 1300 newtons.) So proportionately, the bull shark has the strongest bite of any shark whose jaw strength has been measured. Nobody knows exactly why the shark evolved such a powerful mouth, but it may have something to do with its diet: Bull sharks eat everything from oysters to turtles to other bull sharks, and their herculean jaws might make it easier to tear through a wide range of shells, scales, and skins.

2. THEY THRIVE IN FRESH WATER.

All organisms need a specific salt-to-water ratio within their bodies. This presents a challenge to aquatic life forms—when they absorb too much salt, their cells get dehydrated, but if they take in too much fresh water, the cells get bloated and some of the chemicals inside their bodies may become fatally diluted.

Fish have evolved a couple of tricks to cope with the problem, one of which involves pee. Excess salt is removed from the bloodstreams of oceangoing fish by the kidneys and then flushed out during the urination process. Freshwater fish do the opposite: Their pee contains very little salt and their bodies retain a higher concentration of the substance.

Most fish have no control over how much salt gets removed by their kidneys, which is one reason why many species can only survive in either fresh or salt water. But bull sharks can actually regulate the amount of salt that goes into their pee, which means they can live in both environments. When they swim in the ocean, their urine is highly saline. And as they venture into fresh water, the kidneys work hard to retain salt—thus producing watery, diluted urine. (Bull sharks also use their rectal glands and livers to maintain the proper balance between salt and water.)

3. A BULL SHARK WAS ONCE CAUGHT NEAR ALTON, ILLINOIS.

In 1937, two fishermen captured a 5-foot bull shark more than a thousand miles up the Mississippi River—as far north as this species is known to travel up that river. Given their high tolerance for fresh water, it’s no wonder that bull sharks do well in river systems. One specimen was found swimming in the Amazon River about 2485 miles away from the ocean; they also frequent Africa’s Zambezi River and the Ganges River in south Asia.

4. NOT EVEN HIPPOS ARE SAFE FROM BULL SHARK ATTACKS.

In their trips upriver, bull sharks encounter some of the fiercest predators on earth: In Australia, an 18-foot-long saltwater crocodile named Brutus was once photographed devouring a small bull shark, and in African waterways the sharks have run-ins with hippos. The mammals generate a lot of poop, which attracts small fish that bull sharks eat—so it’s not at all uncommon to see a bull shark or two creeping around a pod of hippos.

The two species don’t always get along. Bull sharks do prey on young hippos on occasion, and adults are sometimes bitten as well—though these attacks might be accidental (in murky, poop-filled water, bull sharks probably mistake hippo legs for fish). Whatever the case may be, large hippopotamuses are adept at fending off bull sharks.

5. UNLIKE GREAT WHITES, BULLS CAN DO WELL IN AQUARIUMS.

No one has been able to keep a great white in captivity for much longer than six months. Bull sharks, however, can live in captivity for 25 years or more. In North America, you can see them at the Oklahoma Aquarium, which houses 10 bull sharks in a nearly 500,000-gallon tank.

6. LAKE NICARAGUA’S RESIDENT BULL SHARKS WERE ONCE THOUGHT TO CONSTITUTE A NEW SPECIES.

Scientists used to think that the large-bodied sharks that periodically attack locals in Lake Nicaragua—the biggest lake in Central America—represented their own, distinct species. A popular hypothesis claimed that Lake Nicaragua must have started out as a bay in the Pacific Ocean that closed up as time went by, trapping some sharks inside that evolved into a brand new species—the so-called “Lake Nicaragua shark,” which ichthyologists called Carcharhinus nicaraguensis.

But Lake Nicaragua isn't cut off from the ocean at all, and scientists eventually determined that “Lake Nicaragua Sharks” are really just bull sharks that were entering the Rio San Juan from the Caribbean and making their way to the lake [PDF].

7. AN AUSTRALIAN GOLF COURSE IS INFESTED WITH THEM.

At the Carbrook Golf Club, located near Brisbane, Australia, tee time sometimes comes with teeth. The course is next to the Logan River, which flooded several times in the 1990s. At some point, newborn bull sharks were probably swept into the brackish, landlocked lake that sits beside tees 12 through 15, and were trapped there when the Logan receded. The lake is spacious (about 50 acres, or the size of Grand Central Terminal) and stocked with fish—good news for the sharks.

The first shark fin sightings were quickly dismissed. “Our members have a tendency to drink a little bit while they play so we really just put that down to too much alcohol,” general manager Scott Wagstaff told National Geographic. But by 2003, there were photos, and a 2011 YouTube video taken by Wagstaff went viral. According to the club’s website, “there are between 6 and 12 sharks” in the lake; the biggest is roughly 9 feet long. It’s also likely that they are breeding.

Carbrook Golf Club celebrates their cartilaginous guests: “Shark Lake Challenge” tournaments are held on the last Wednesday of every month and a stylized shark fin adorns the club logo. For obvious reasons, ball retrieval has been prohibited.

8. BITING IS A PART OF MATING.

Male bull sharks become sexually active at 14 or 15, but females don’t start reproducing until they're 18. Female bull sharks of reproductive age have scars behind their skulls: A male bites his partner to hang on during coitus (a behavior that appears to be common), then uses one of his claspers—a pair of fin extensions located under the pelvic area—to insert sperm into her cloaca.

Following a 10- to 11-month gestation period, the female will give birth to a litter of pups. Newborns typically range between 22 and 32 inches long.

9. ONLY TWO OTHER SHARK SPECIES BITE HUMANS MORE OFTEN.

All types of shark-on-human attacks are ultra-rare—you’re more likely to get struck by lightning. But the three shark species that are most commonly implicated in attacks on people are, in order, the great white shark, the tiger shark, and the bull shark. Bull sharks have been involved in at least 100 documented cases, and there's an explanation for that: They frequent shallow, coastal waters in tropical regions and often stray into brackish and fresh water—all places where humans can be found. In areas where the sharks can’t see very well, they may mistake humans for other, meatier prey.

Since bull sharks lack eye-catching markings or facial features, it can be difficult to identify them. This is why some experts wonder if bull sharks might have been responsible for certain attacks that were blamed on great whites, Ganges river sharks (Glyphis gangeticus), or other species.

10. A BULL SHARK MAY HAVE PARTICIPATED IN THE FAMOUS NEW JERSEY SHARK ATTACKS OF 1916.

On July 1, 1916, a 25-year-old swimmer was bitten by a shark off the coast of New Jersey's Long Beach Island. Though a lifeguard managed to rescue him, the man died of blood loss. Five days later, a bell captain lost both legs in a shark attack near Spring Lake. He too died. Farther north, a boy and an adult man were killed by a shark in Matawan Creek on July 12. Within 30 minutes, a teenager was bitten less than a mile downstream, but he survived.

All five attacks have historically been pinned on a single 8-foot-long great white that was captured and killed on July 14 in Raritan Bay, just a few miles away from the Matawan attacks. Inside its stomach were human remains. No subsequent shark attacks were reported in New Jersey that summer.

But the situation might not be so clear-cut: The two Matawan Creek incidents occurred 11 miles from the ocean, and great whites don't travel to shallow inland waters. Bulls are also more abundant off the Jersey shore than great white sharks are. That leads some experts, including explorer Fabien Cousteau, to conclude that a bull shark was the real culprit. Shark attack expert George Burgess still thinks the evidence points to the great white with a bellyful of body parts. It’s also possible that more than one shark committed the 1916 attacks.

11. NO, BULL SHARKS DON’T HAVE THE ANIMAL KINGDOM’S HIGHEST TESTOSTERONE LEVELS.

According to the internet, some books, and Grand Theft Auto, bull sharks are extra-aggressive because they have more testosterone than any other animal. In reality, very little research has been done on the subject of bull shark hormones. One study compared the testosterone levels in three bull sharks: The female had a low testosterone level (0.1 nanograms per milliliter), one of the males had only 2.7 nanograms per milliliter, and the other male had a ludicrously high testosterone level of 358 nanograms per milliliter—so the results were inconclusive. Bonnethead sharks and rainbow trout both have extreme testosterone levels, so in that regard, bull sharks aren’t special. At least they can still brag about their jaws.

nextArticle.image_alt|e
iStock
Potato-Based Pet Food Could Be Linked to Heart Disease in Dogs
iStock
iStock

If you have a pup at home, you may want to check the ingredients listed on that bag of dog food in your cupboard. The U.S. Food & Drug Administration has warned that potato-based pet foods might be linked to heart disease in dogs, Time reports.

Foods containing lentils, peas, and other legume seeds are also a potential risk, the agency’s Center for Veterinary Medicine announced.

“We are concerned about reports of canine heart disease, known as dilated cardiomyopathy (DCM), in dogs that ate certain pet foods containing peas, lentils, other legumes or potatoes as their main ingredients,” Martine Hartogensis of the veterinary center said in a statement. “These reports are highly unusual as they are occurring in breeds not typically genetically prone to the disease.”

Recent cases of heart disease have been reported in various breeds—including golden and Labrador retrievers, miniature schnauzers, a whippet, a shih tzu, and a bulldog—and it was determined that all of the dogs had eaten food containing potatoes, peas, or lentils.

While heart disease is common in large dogs like Great Danes and Saint Bernards, it’s less common in small and medium-sized breeds (with the exception of cocker spaniels). If caught early enough, a dog’s heart function may improve with veterinary treatment and dietary changes, the FDA notes. While the department is still investigating the potential link, it’s best to err on the side of caution and avoid foods containing these ingredients until further notice.

As shown by the recent romaine lettuce scare linked to E. coli, the FDA is unable to request a food recall unless a specific manufacturer or supplier can be identified as the source of contamination. Instead, public notices are generally issued to warn consumers about a certain food while the agency continues its probe.

[h/t Time]

nextArticle.image_alt|e
iStock
10 Science-Backed Tips for Getting a Cat to Like You
iStock
iStock

Like so many other humans, you might find cats to be mysterious creatures. But believe it or not, it’s not that hard to make friends with a feline, if you know what to do. Here are some tips on how to effectively buddy up with a kitty, drawn from scientific studies and my own experience as a researcher and cat behavioral consultant.

1. LET THE CAT CALL THE SHOTS.

When we see cats, we really want to pet them—but according to two Swiss studies, the best approach is to let kitty make the first move.

Research done in 51 Swiss homes with cats has shown that when humans sit back and wait—and focus on something else, like a good book—a cat is more likely to approach, and less likely to withdraw when people respond. (This preference explains why so many kitties are attracted to people with allergies—because allergic people are usually trying to not pet them.) Another study found that interactions last longer and are more positive when the kitty both initiates the activity and decides when it ends. Play a little hard to get, and you might find that they can’t get enough of you.

2. APPROACH A CAT THE WAY THEY GREET EACH OTHER (SORT OF).

person extending finger to cat's nose
iStock

Felines who are friendly with each other greet each other nose to nose. You can mimic that behavior by offering a non-threatening finger tip at their nose level, a few inches away. Don’t hover, just bend down and gently extend your hand. Many cats will walk up and sniff your finger, and may even rub into it. Now that's a successful greeting.

3. PET CATS WHERE THEY LIKE IT MOST …

They're very sensitive to touch, and generally, they tend to like being petted in some places more than others. A small 2002 study demonstrated that cats showed more positive responses—like purring, blinking, and kneading their paws—to petting on the forehead area and the cheeks. They were more likely to react negatively—by hissing, swatting, or swishing their tails—when petted in the tail area. A more recent study validated these findings with a larger sample size—and many owners can testify to these preferences.

Of course, every animal is an individual, but these studies give us a good starting point, especially if you're meeting a cat for the first time.

4. … AND IF YOU GET NEGATIVE FEEDBACK, GIVE THE CAT SOME SPACE.

There are plenty of signs that a cat doesn't like your actions. These can range from the overt—such as hissing and biting—to the more subtle: flattening their ears, looking at your hand, or twitching their tails. When you get one of those signals, it’s time to back off.

Many of the owners I work with to correct behavioral issues don't retreat when they should, partially because they enjoy the experience of petting their cat so much that they fail to recognize that kitty isn’t enjoying it too. You can’t force a feline to like being handled (this is especially true of feral cats), but when they learn that you’ll respect their terms, the more likely they will be to trust you—and come back for more attention when they're ready.

5. DON’T OVERFEED YOUR CAT.

Many think that food equals love, and that withholding food might make your kitty hate you, but a recent study of obese felines from Cornell University showed the opposite is true—at least for a period of time. About a month after 58 overweight kitties were placed on a diet, three-quarters of their owners reported that their dieting felines were more affectionate, purred more often, and were more likely to sit in their owner's lap. This adorable behavior came with some not-so-cute side effects—the cats also begged and meowed more—but by week eight, both the good and bad behavior had abated for about half the animals.

Regardless of whether a diet makes your pet cuddlier, keeping your pet on the slender side is a great way to help them stay healthy and ward off problems like diabetes, joint pain, and uncleanliness. (Overweight animals have difficulty grooming themselves—and do you really want them sitting on your lap if they can’t keep their butt clean?)

6. PLAY WITH THEM—A LOT.

woman, cat, and feather toy
iStock

Most of the behavior problems that I've witnessed stem from boredom and a lack of routine playtime. No one thinks twice about walking their dog every day, but many people fail to recognize that felines are stealth predators who need a regular outlet for that energy. A recent study suggested that cats prefer human interaction over food, but a closer look at the data demonstrated that what really attracted them to humans was the presence of an interactive toy. One of their top choices is a wand-style toy with feathers, strings, or other prey-like attachments that evoke predatory behavior. Daily interactive play is a great way to bond with them when they’re not in the mood to cuddle—and to keep them fit. Try the Go-Cat Da Bird or any of Neko Flies interchangeable cat toys.  

7. KEEP YOUR CAT INDOORS.

A study conducted in Italy showed that felines who stayed mostly indoors (they had one hour of supervised access to a small garden each day) were more “in sync” with their owners than felines who were allowed free access to the outdoors. The indoor kitties were more active during the day, when their owners were likely to be active, and less active at night, when humans like to sleep. (Many people believe cats are nocturnal, but they are naturally crepuscular—active at dawn and dusk.)

8. SOCIALIZE CATS WHEN THEY'RE YOUNG.

Multiple studies have shown that just a few minutes a day of positive handling by humans helps kittens grow up to be friendlier and more trusting of humans. The ideal age to socialize kittens is when they're between 2 and 9 weeks old. One 2008 study found that shelter kittens that had been given a lot of "enhanced socialization"—additional attention, affection, and play—were, a year later, more affectionate with their owners and less fearful than other kittens adopted from the same shelters.

You can help socialize kittens by volunteering as a foster caretaker. Fostering ensures they get plenty of interaction with people, which will help them will be comfortable around potential adopters. You'll also be doing your local shelter a huge favor by alleviating overcrowding.

9. TAKE THE CAT'S PERSONALITY—AND YOUR OWN—INTO CONSIDERATION WHEN ADOPTING.

If you want to adopt an older animal, take some time at the shelter to get to know them first, since adopters of adult cats report that personality played a big role in their decision to take an animal home permanently and had an impact on their satisfaction with their new companion. Better yet, foster one first. Shelters can be stressful, so you'll get a better sense of what an animal is really like when they're in your home. Not all cats are socialized well when they're young, so a cat may have their own unique rules about what kinds of interactions they're okay with.

It's also key to remember that a cat's appearance isn't indicative of their personality—and it's not just black cats who get a bad rap. In 2012, I published a study with 189 participants that showed that people were likely to assign personality traits to felines based solely on their fur color. Among other things, they tended to think orange cats would be the nicest and white cats the most aloof. (Needless to say, these are inaccurate assumptions.) And it's not just the kitty's personality that matters—yours is important too. Another study I conducted in 2014 of nearly 1100 pet owners suggested that self-identified “cat people” tend to be more introverted and anxious when compared to dog people. (We’re also more prone to being open-minded and creative, so it’s not all bad.) If you’re outgoing and active, a more playful feline could be for you. If you prefer nights spent snuggling on the couch, a mellow, shy-but-sweet lovebug could be your perfect pet.

10. BE A KEEN OBSERVER OF THEIR BEHAVIOR.

Overall, use your common sense. Be a diligent and objective observer of how they respond to your actions. Feline body language can be subtle—something as small as an eye-blink can indicate contentment, while ear twitches might signal irritation—but as you learn their cues, you'll find yourself much more in tune with how they're feeling. And if you adjust your behaviors accordingly, you'll find soon enough that you've earned a cat's trust.

Mikel Delgado received her Ph.D. at UC-Berkeley in psychology studying animal behavior and human-pet relationships. She's a researcher at the UC Davis School of Veterinary Medicine and co-founder of the cat behavior consulting company Feline Minds.

SECTIONS

arrow
LIVE SMARTER
More from mental floss studios