Scientists in Australia have called for swimming advice to be updated to reflect new information about one of the most dangerous shark species. The call came after researchers tracked the movements of bull sharks off the coast of New South Wales and found the times when the largest individuals are most active.

Currently, advice states that swimming and surfing should be avoided at "dawn" and "dusk" as this is when visibility is poorest and when sharks are more active — both factors that increase the risk of attacks.

However, researchers from the New South Wales Department of Primary Industries and Macquarie University argue swimmers should avoid the water during the afternoon and low-light conditions as well.

Amy Smoothey, scientific officer and shark biologist at the New South Wales Department of Primary Industries, and one of the lead investigators in the study published in the journal Biology on Aug. 31, said the team tracked 233 tagged bull sharks (Carcharhinus leucas) along 21 coastal beaches in New South Wales between 2017 and 2023 to find out when they are closest to shorelines.

Related: Great white sharks have almost no interest in eating humans, study confirms

"We found that the presence of large bull sharks was greatest from midday through to 4 a.m.," she told Live Science in an email, adding there was an increased probability of the sharks being near the shore between 6 p.m. and 1 a.m.

The researchers found there are certain conditions that increase the chances of encountering a large bull shark. These include when the water temperature is higher than 68 degrees Fahrenheit (20 degrees Celsius), after heavy rain or when the water is murky.

"These conditions are favourable for ambush predators like bull sharks," Smoothey said. "Be aware during periods of low-light levels, as these are times when bull sharks are typically more active and you may not be able to see the approaching shark."

Bull sharks are one of the three species involved in most fatal attacks in Australia, along with great white sharks (Carcharodon carcharias) and tiger sharks (Galeocerdo cuvier). Bull sharks, which can grow to around 11 feet (3.4 meters) long, are generally considered to be particularly dangerous as they have a preference for warm coastal waters and can travel up rivers. The most recent fatal attack by a bull shark in Australia occurred in February this year, when 16-year-old Stella Berry was attacked in a river in Perth.

However, the researchers highlighted that unprovoked shark bites are rare. According to the University of Florida's International Shark Attack File, there were a total of 57 unprovoked bites by all species of sharks globally in 2022, most of which occurred in the United States and Australia. Of these, five attacks were fatal.

Smoothey said that the researchers recommend an update to advice about shark safety, but that current guidelines are still important. "We concur with the current shark smart advice that nocturnal swimming and surfing, especially in warm waters and when water visibility is poor, should be avoided for many reasons, not the least of which being the presence of bull sharks," she said.

Editor's note: The original image on this article was of a sand tiger shark (Carcharias taurus). The image has been updated with to show a bull shark.

Martin Richardson was swimming in the Red Sea in Egypt when he was attacked by a mako shark (Isurus oxyrinchus). He was bitten approximately five times and was waiting to die when something unusual happened. 

"There was no reason for the shark to stop," he said in "Saved from a Shark," a new show from National Geographic. "I had lost approximately 5 pints [2.8 liters] of blood. You only have 8 to 9 [pints, or 4.5 to 5 L] in your body. I was waiting for a feeding frenzy… I knew it was circling me… I turned away and looked at the mountains. I gave up."

At this moment, a group of dolphins appeared just behind Richardson, and the attack stopped. He was then pulled onto a boat that had been racing to get to him before the shark did and rushed to hospital, where needed more than 300 stitches. "I firmly believe the dolphins saved my life," he said. 

Related: Great whites are dining on other sharks instead of seals, researchers discover in NatGeo show

Do whales and dolphins really protect humans from sharks? "Saved from a Shark" — part of NatGeo's SharkFest — looks closely at four cases where people were seemingly protected from the predators in the water."Being saved by another animal is certainly a very romantic notion," Tom Hird, marine biologist and shark conservationist, said in the program. 

But it's not so clear that's what's actually going on in most cases. 

Mike Heithaus, professor in the department of biological sciences at Florida International University, said it's unlikely dolphins were intentionally saving Richardson's life. 

"The dolphins see a big cloud of blood, they know a shark is in the area." If they had young, they'd want to scare the shark away from the young. "They may not have been trying to save Martin," he said in the show. 

In another case explored in the film, Nan Hauser, director of the Cook Islands Whale Research, revisited the moment in 2017 when a humpback whale (Megaptera novaeangliae) she was diving with saved her from a huge tiger shark (Galeocerdo cuvier) that was stalking her. In footage shot during the encounter, Hauser is approached by the whale, pushed and then lifted onto its snout. 

"[The whale is] looking at me and I know he's got something to tell me," she said in the program. "I do not understand. He wants me to understand. I look down into the deep blue. And I then I see [the tiger shark] right below me.

"I know — and the whale knows — this is a serious situation and I want to get out of the water. Then all of a sudden I was swooped up by the whale… now he's got me right on the front of his face."

The footage captured shows the whale engaging in a behavior similar to what it would do to protect a calf, Heithaus said.

Howether, Heithaus said the most unusual case was when a group of lifeguards swimming off the coast of New Zealand were encircled by a group of dolphins. Unbeknownst to the group, a great white shark (Carcharodon carcharias) was stalking them. "I'm used to having dolphins swimming alongside me, but this was totally different," Rob Howes, one of the lifeguards in the water, said in the program. 

One of the larger male dolphins charged towards him, and he then realized it was targeting the approaching shark. "Everything built to a big crescendo. Then everything went calm. The shark disappeared very quickly. It was bizarre."

Heithaus said in most cases, whales and dolphins are probably not protecting humans for altruistic reasons — more likely they are trying to protect themselves or their young. But with the lifeguards in New Zealand, "this is one case where it really seemed like the dolphins were protecting people," he told Live Science in an email. 

"Saved From a Shark" premieres on Disney+, Hulu, and National Geographic on July 2. Check out our how to watch Shark Fest 2023 guide if you want to catch up on all the shark-centric shows dropping in July.

Would you let a humpback whale beat you up to save your life?

Marine biologist Nan Hauser did not realize she was answering this question last October when a giant, perhaps 50,000-pound (22,700 kilograms) humpback swam up to her in the waters off the Cook Islands, and began lifting her out of the ocean with its massive head. Over the tense 10 minutes that followed, Hauser swam calmly around the whale as it nudged her with its head, bumped her with its belly, and swiped at her with its powerful pectoral fins.

"I've spent 28 years underwater with whales, and have never had a whale so tactile and so insistent on putting me on his head, or belly, or back, or, most of all, trying to tuck me under his huge pectoral fin," Hauser, president of the Cook Islands-based Center for Cetacean Research and Conservation, told the Daily Mirror.

"If he rammed me too hard, or hit me with his flippers or tail, that would break my bones and rupture my organs. If he held me under his pectoral fin, I would have drowned … I was sure that it was most likely going to be a deadly encounter."

Hauser was nearly right, but not in the way she thought. Only after finally surfacing and returning to her team's research vessel did she notice another unexpected visitor swimming nearby: a 15-foot-long tiger shark, lurking on the other side of the whale.

Amazingly, Hauser and her team caught the entire encounter on video, which she shared for the first time Monday (Jan. 8). The footage, she is now sure, shows that the heroic humpback is not trying to attack her, but is shielding her instead from an even deadlier shark.

Aquatic altruists

This is not the first time a humpback whale has been observed intervening in a would-be marine ambush — in fact, the humpback's so-called "altruism" is well-documented.

In 2009, for example, marine biologist Robert Pitman snapped an incredible photo of a humpback cradling a Weddell seal to its chest while rolling out of the water, shielding the seal from a group of hungry killer whales.

Pitman went on to analyze 115 interactions between humpbacks and killer whales between 1951 and 2012, and determined the act of seal-saving derring-do he witnessed was hardly a freak occurrence. Humpbacks, Pitman wrote, frequently band together and sometimes travel great distances to interrupt killer whale attacks, regardless of what type of animal the orca is attacking. [In Photos: Tracking Humpback Whales]

The humpback's shielding impulse likely comes from an instinct to protect its own calves from predators, Pitman said. Because massive humpbacks have little to fear from orcas, the risk of intervening in or even initiating a fight to save their young may be well worth the risk.

"A simple behavioral rule like 'interfere with attacking killer whales' may prevent a related calf from being killed," Pitman previously told Live Science, "and it may also help out other species at times. I think we need to consider the possibility that altruism can be unintentional and arise out of self-interest."

Researchers again caught a glimpse of a humpback's seeming altruism in May 2017, when a group of the cetacean crusaders interrupted a pod of killer whales that were stalking some baby gray whales off Monterey Bay in California.

Hauser thinks it's likely that the whale that head-butted her was similarly trying to protect her from the predator in their midst (she later learned that, while one humpback was focused on her, another was swatting the water near the tiger shark, seemingly keeping it at bay). However, this marks the first known instance of a humpback intervening to shield a human from a shark, Hauser said.

Whether the humpback's heroics were instinct, accident or altruism, Hauser was quick to show her gratitude. At the end of the video, the whale surfaces just as Hauser — a bit scraped and bruised from their encounter, but in overall fit shape — climbs back aboard her team's boat. As if checking in with her, the whale blasts a quick gout of water into the air from its blowhole.

"I love you, too," Hauser calls back. "I love you, too!"

Originally published on Live Science.

Here's an image no swimmer would want to see in real life: a massive tiger shark with its jaws open, as if ready to devour an observer.

Though the picture makes it look like the photographer was the shark's next meal, no one was ever in danger, said David Shiffman, a doctoral candidate in marine biology at the University of Miami's Abess Center for Ecosystem Science and Policy, who posted the photo on Twitter (but was not on the boat at the time the photo was taken).

Researchers captured the photo during a tagging project aimed at better understanding tiger sharks' migration patterns. Knowing where the sharks feed, breed and live could help politicians craft protected areas for the overfished species.

The sharks travel huge distances, with some swimming to the middle Atlantic Ocean or to South America from the Bahamas, though it's often not clear exactly why they do it.

Several weeks ago, Shiffman's colleagues captured a tiger shark off the coast of Florida and brought the animal onto the semi-submerged platform behind their boat, with water still buoying the shark's body. The researchers propped the predator's mouth open with a hook, and gently restrained the animal as they collected samples. A photography intern, Cat Schultz, got the scary photo before the shark moved.

"The shark's mouth was open enough to take that quick shot," Shiffman told LiveScience.

The tiger shark is an opportunistic generalist, feeding on seabirds, ocean-dwelling mammals and even turtles. Some scientists have even found tiger sharks with suits of armor or license plates in their bellies.

"People call them the garbage disposals of the oceans," Shiffman said.

Their mouths are key to their indiscriminate eating habits. In order for the sharks to chomp through a sea turtle shell, they need to have a powerful bite force. Even as babies, their mouths are disproportionately large, the better to engulf unsuspecting prey.

"When they're babies, they're basically all head," Shiffman said.

Follow Tia Ghose on Twitter and Google+. Follow LiveScience @livescience, Facebook & Google+. Original article on LiveScience.

Dangers in the Deep

On land during the day, we humans rule. Or at least we're considered top predators, and with our feet on the ground, we're in our element.

In the sea, sans a boat, forget about it. We're too slow, too encumbered with gear, and often too stupid to be much more than prey. What's to worry about down there? Plenty!

Yes, this list is subjective, but it's based on research aimed at finding the creatures of the deep that conjure the most compelling combination of frightening personas, actual aggression and/or real pain or death to humans. More often than not, pain and death from sea creatures is avoidable, especially in the case of two on this list that inflict most of their damage in home aquariums and restaurants.

Before we continue, a nod to venerable contenders that aren't on the list: killer whales (there are few confirmed attacks, accept by those in captivity), octopuses (yes, they've been known to attack), sea cucumbers (who'da thunk?) and piranhas (which actually live only in freshwater, and whose deadly attacks on people are pure myth).

Box Jellyfish

These gelatinous creatures are flat-out deadly.

While no official tallies exist, anecdotal evidence suggest dozens of people and perhaps more than 100 or more die each year from the many species of box jellyfish that exist in all oceans.

Some 20 to 40 people die from stings by box jellyfish annually in the Philippines alone, according to the U.S. National Science Foundation. "But because death certificates are not required in many countries within the range of box jellyfish, worldwide fatalities from box jellyfish may be seriously underestimated," the NSF states.

One Australian box jellyfish can have dozens of tentacles, each up to 15 feet long, with enough toxin to kill 60 people. The sting of a Chironex fleckeri box jellyfish can kill a person in less than three minutes. Species of box jelly fish in Hawaii, Florida and other U.S. locations are known to induce heart failure.

Honorable mention goes to the Portuguese man-of-war, a jellyfish with a sting said to be as painful as a lightning strike — though it's not clear how many people are actually able to make that comparison.

Tiger Shark

Yeah, yeah, the great white shark gets all the attention. But reality is tiger sharks kill more people. And few things (other than snakes) automatically terrify people more than sharks.

Tiger sharks will eat anything: fish, seals, birds, squid, small sharks, dolphins, license plates and pieces of old tires, according to NOAA. They can grow more than 18 feet long and weigh a ton. Take that, Jaws!

Tiger sharks are found in many tropical and temperate waters, and they are especially common around islands in the central Pacific. For the record: Great whites do attack more people each year, on average.

Oh, and a little detail that explains why sharks aren't No. 1 on this list: The number of people attacked by sharks worldwide each year — a few dozen — is roughly equal to the number killedby lightning just in the United States. Only four people around the world died from shark attacks last year.

Stonefish

This one nearly tops the list for two reasons: It's the most venomous fish in the world, and it's a master of disguise, hiding in plain sight on the seafloor, looking like any other rock.

The stonefish doesn't attack, but you don't want to step on it. Its spines are used as defense against sharks and other predators. The venom can cause temporary paralysis and death if not treated.

Pufferfish

You don't even have to be near water for this creature to kill you. The pufferfish, also known as a blowfish, packs tetrodotoxin — stronger than cyanide. Specially trained Japanese chefs prepare safe parts of the fish as a delicacy, but every now and then a diner dies.

The puffer, named for its ability to suck in water and swell to twice normal size, could end up saving people: a drug made from the puffer's toxin has been tested for treatment of withdrawal symptoms from drugs like heroin.

Sea Snake

The innate human fear of snakes propels these slithering swimmers to the list. However, the truth is that while sea snakes out-venom their terrestrial counterparts, they're highly reclusive and so not much of a threat.

Lionfish

Popular in home aquariums, these docile fish sport a striking fan of venomous spines.

Although not fatal to humans, the spines deliver a painful sting that can cause headaches, vomiting, and respiratory distress, according to NOAA. The worst of the pain typically lasts only for about an hour, but some people report pain and tingling sensations for weeks.

Lionfish are not aggressive. So the fact is home aquarium owners are more likely to be stung by lionfish than divers or fishermen.

Crocodile

Saltwater crocs have earned a reputation as one of the wild kingdom’s most ferocious predators.

They can grow more than 20 feet long and weigh 3,000 pounds, and they have been known to hunt a wide range of prey, including monkeys, kangaroos, buffalo and even sharks.

Relying on purely brute strength, they are capable of dragging down water buffaloes and have occasionally victimized humans. Using an attack method known as the “death roll,” crocodiles kill their prey by latching on with their jaws and then taking down the dinner with a powerful, twisting roll. The technique is also employed to break apart large animals.

Stingray

Just the name practically qualifies these creatures for this list. And the death of "Crocodile Hunter" Steve Irwin by stringray in 2006 certainly solidified the reputation of these shark cousins as dangerous beasts.

The tail of of a stingray is capped with a roughly 8-inch spear made of the same stuff that makes up shark scales, known as dermal denticles. The spear, which stiffens when the stingray feels threatened, is serrated like a steak knife and packs a venom that can be deadly to predators.

"The venom itself is a largely protein-based toxin that causes great pain in mammals and may also alter heart rate and respiration," according to the Mote Marine Laboratory.

Stingrays don't typically attack humans, however.

Sea Lion

Really? Sea lions? Yes, because they're very territorial.

They’re considered cute, trainable and are major attractions at zoos, but have been known to bite people.

In California, a spate of vicious sea lion attacks reported at Manhattan beach, Newport beach and San Francisco back in 2006 led to growing concern among caretakers and scientists. Some researchers suspect the sea lions may have eaten fish contaminated by toxic algae, which may explain the uncharacteristic behavior.

The city of San Diego warns on its web site “Like all wild animals, seals and sea lions are unpredictable and can become aggressive quickly. They have sharp teeth and may bite, particularly if cornered or harassed.”

Moray Eel

Snakelike body, protruding snout and wide jaws. These primitive creatures just look like death. They're fish, by the way, and they can be up to 8 feet long.

A bite from their razor-sharp teeth and powerful, locking jaws will produce ragged wounds that are prone to infection from the bacteria inside the eels’ mouths, according to NOAA. The good news: If morays bite out of fear or by accident (especially when foraging for food), they will usually release their grip and let you go.

They tend to hide in crevices and holes during the day, then hunt at night. They'll eat any fish or other creature they can catch.

Some expert advice, from NOAA, on how to avoid being bitten by one: Keep your hands out of submerged, rocky holes and crevices. Oh, and avoid this common diver gaffe that leads to many moray eel bites: Don't feed them!

A digital rendering of a great white shark's maw could lead to the first accurate estimate of the power behind a full-force bite.

The shark's ability to inflict killer damage on anything it grabs, however, probably is due to saw-like teeth and not the amount of bite force, the study researchers say. Once a great white clamps down on a prey with its razor-sharp teeth, the shark often shakes the catch from side to side to initiate a sawing action.

Daniel Huber, a biologist at the University of Tampa in Florida, examined an eight-foot (2.4-meter) great white shark that had died after becoming entangled in nets off the coast of Australia. Huber and his colleagues dissected the shark's head and took several measurements, including the size and placement of the jaw muscles.

"We are figuring out in three dimensions the leverage of all of these jaw muscles," Huber told LiveScience. The jaws work like a set of pliers, where pliers with long handles would let you grab an item with more force than pliers with short handles.

From this data, the researchers are developing a 3-D digital recreation of the shark and a computer simulation of a full-force bite. They will compare the final force estimate with those from tiger and bull sharks, which, along with the great white, are responsible for most shark attacks on humans.

“The white has the narrowest head of the three, so it has less space for jaw muscles,” Huber said. “Consequently, we’re expecting that it will have a lower bite force on a pound-for-pound basis.”

But great whites would still top the charts as savviest hunters and most adept at capturing prey.

“Much of the damage inflicted by white sharks is due to their teeth, and not necessarily to the force,” Huber said.

The research is being sponsored by the University of New South Wales, University of Tampa, University of Newcastle in Australia and the Computational Biomechanics Research Group.

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