A tragic encounter with a bull shark left one survivor with a newfound purpose. An Australian survivor of a severe shark attack, who faced the loss of a hand and leg in the assault, has identified the key triggering element that compels these apex predators to bite humans, likening it to a ‘dinner bell.’
Paul De Gelder, an ex-Australian military member, was grievously injured in 2009 during a counterterrorism exercise that took place in Sydney Harbor. The life-altering event, however, steered De Gelder toward becoming an advocate for shark conservation.
Now renowned as a shark conservationist, De Gelder regularly features in Discovery’s annual ‘Shark Week.’ In his latest contribution, the show ‘Bull Shark Dinner Bell,’ set to air Monday at 8 p.m. ET, De Gelder unpacks three crucial elements that can provoke bull shark attacks across the globe.
On the Florida coast, expert Rosie Moore conducted experiments revealing that certain conditions can entice bull sharks near humans. Rainstorms combined with vibrations from activities like diving or fishing in waters rich with fatty fish can lure these fearsome predators, prompting them to strike.
Despite there being around 500 shark species that typically avoid human contact, bull sharks are an exception. Known as ‘ambush predators,’ they thrive in temperate waters, making them more likely to come into close proximity with humans, especially under enticing conditions.
They are the number one suspect in most of the world’s shark attacks, and 10 biting incidents have already been blamed on them in 2026, according to the Global Shark Attack File, a public database documenting cases as far back as the 1940s.
De Gelder said during a new Shark Week special: ‘If you go through the Global Shark Attack Files since 2025, bull sharks are responsible for twice as many attacks as tiger sharks, and even 25 percent more than great whites.’
‘If they chose to, they could kill you, but they more often than not don’t.’
Pictured: A bull shark swims in the ocean. Wildlife experts have warned that this species is not afraid to swim near people (Stock Image)
Paul De Gelder (Pictured in 2009) lost his right hand and leg in a shark attack during a military exercise in Australia
De Gelder traveled to Florida, the bull shark capital of the US, to team with Moore to figure out why bull shark attacks have been on the rise and what humans are doing to set off the ‘dinner bell.’
Moore said on the Discovery Channel: ‘With bull sharks, there’s usually a number of factors that lead up to that bite.’
They traveled to Jupiter Ledge, a bull shark hotspot near Palm Beach, where the predators immediately gathered around their boat.
One constant factor tied to bull shark attacks has been rain, with researchers believing that storms potentially agitate the creatures by making countless vibrations on the surface of the ocean.
Moore dove into the Atlantic near a pack of five to six bull sharks, while De Gelder activated a water pump which simulated rainfall. It instantly attracted more sharks to the area, which were moving faster as the rain came down.
‘I think the bull sharks might associate the raindrops on the surface with other fish. They detect the tiniest vibrations. They can literally see with their eyes closed,’ Moore explained.
She added these extraordinary sensors allow sharks to hunt even in the darkest waters.
‘The rain has definitely triggered a more aggressive response. They’re faster, bolder, more willing to bite,’ Moore said. ‘Rain is definitely a factor we need to ring this dinner bell.’
Pictured: Predators swarm a crate of food researchers lowered into the Atlantic to discover which type of fish meat attracts bull sharks
Apex predator specialist Rosie Moore (Pictured) discovered three key factors which cause bull sharks to attack humans in a new ‘Shark Week’ special airing on July 27 on Discovery
Since the sharks clearly showed a desire to swarm near the ocean surface and attack live fish during rainstorms, the team also tested different types of bait, including lean fish meat like grouper and oily and fatty fish like bonito.
De Gelder and Moore brought a crate of each meat type down into the open water of the Atlantic, and watched as a group of bull sharks bumped and headbutted the boxes – a behavior they engage in before attacking potential prey.
Oddly, when the team dropped in a third crate full of pork to simulate human flesh and blood, the bull sharks ignored the meat.
Instead, the predators chose to attack the crate full of oily and fatty fish when hunting, which Moore and De Gelder said was a critical clue as to what sets off the dinner bell for the deadly sharks.
Moore explained: ‘By knowing what seasonal fish migration patterns overlap with the bull shark populations, that can help us advise people on when they should stay out of the water because the sharks might be hunting.’
Pictured: Multiple bull sharks swarm in Jupiter Ledge, a hotspot for the species near Florida’s Palm Beach
De Gelder returned to bull shark-infested waters near Florida to research what causes them to attack people for Discovery’s ‘Shark Week’
The researchers then looked at how human behavior could trigger a bull shark attack, since these creatures, like other shark species, are highly sensitive to vibrations.
One activity that has been frequently tied to bull shark attacks is spearfishing.
While De Gelder caught a fish with a speargun from the boat, Moore watched in scuba gear as a bull shark charged in to attack the struggling fish. Nearly a dozen more bull sharks moved into the area to bump Moore and her cameraman.
‘Bull sharks are interesting because it’s almost like they get a sense of FOMO. It triggers an uptick in aggression from the other sharks around it because if you’re a shark in the ocean, there’s not necessarily a grocery store for you to go to; you have to compete for that available prey,’ Moore said.
In one final experiment, De Gelder tested the reactions of the sharks by jumping into the ocean, triggering a massive splash and vibration.
‘As soon as I hit the water they came to investigate,’ De Gelder said.
The sharks were seen putting both pectoral fins down, a sign they were extremely agitated, with one shark actually biting De Gelder’s scuba fin.
A bull shark and another, smaller shark were spotted in early July 2026 off the New York coast, triggering bans on swimming for beachgoers
When the team put all of these factors together – rainfall, the presence of oily and fatty fish meat and a human diving directly into an area with sharks – the bulls immediately moved to attack De Gelder.
‘As soon as I hit the surface with the rain, the bait in the water, it was like the perfect storm,’ he said.
Not only were the bull sharks agitated, but it also attracted more sharks to the area and caused the predators to attack one another.
‘I have never seen bull sharks behave like this,’ Moore declared. ‘You can literally see how if all these elements lined up and you had somebody in the water that was not prepared, they would not stand a chance. The dinner bell has rung.’
Moore noted that there were ways to peacefully coexist with sharks, but certain conditions, including rainfall, fatty fish in the area and too much human activity disrupting the water, create a deadly recipe for a shark attack.
‘Truly assess the conditions before you enter the water, it could save your life,’ De Gelder said.