Weipa is a small coastal mining town in Queensland, located in northeastern Australia, particularly loved by anglers for its annual competition, the Weipa Fishing Classic. But in recent years, anglers have reported an increasing number of incidents of local bull sharks launching daring underwater attacks, literally waiting for a fish to hook and chew it off the line. Some fishermen estimate they could lose as much as 70 percent of their catch to the sharks, which appear to target fishing boats specifically.
(Some spoilers for the documentary below the gallery.)
It’s atypical behavior for bull sharks, and it raises an interesting question: Is this evidence that this shark species — known in the popular imagination (a bit unfairly) as aggressive “mindless killers” — is more intelligent than previously believed? That’s one of the questions shark biologists Johan Gustafson and Mariel Familiar Lopez set out to answer, and their first fieldwork has been documented for posterity in Bull Shark banditspart of National Geographic’s SHARKFEST programming for 2023. SHARKFEST will run for four full weeks of “explosive, hair-raising and celebratory shark programming that … showcases the captivating science, power and beauty of these magnificent animals,” according to the official description.
The fishing behavior is technically known as predation. Among other factors, Australian fish stocks have declined by more than 30 percent over the past decade, and the sharks seem to be adapting accordingly, teaching the behavior to their fellow sharks.
“Many different species are doing it, including dolphins and killer whales, which are high-level predators, but shark predation in particular is happening all over Australia right now,” Gustafson told Ars. “In areas where there is a higher fishing pressure, the behavior occurs more often or more intensely. We call it habituation. They have acquired a habit, they actually learn from each other, and they spread it around [the population].”
bull sharks (Carcharhinus leucas) are found all over the world and usually prefer warm, shallow coastal waters and freshwater rivers. It is not a true freshwater species, but the females usually give birth upstream, as such places provide a more protective environment for nurseries. (Sharks don’t raise their young; baby sharks usually join the adult ocean population when they are about eight years old.) Bull sharks usually grow to an average of six feet (2 meters) in length (for males) and eight feet (for females), and their powerful bite can generating as much as 1330 pounds of force (5914 newtons).
Bull sharks are considered opportunistic eaters, meaning they eat in short portions during times of scarcity and digest for longer periods of time. Their diet favors bony fish and smaller sharks (including their fellow bull sharks), as well as turtles, birds, dolphins and crustaceans. They are also fairly territorial and solitary, preferring to hunt alone or occasionally in pairs.
Their reputation for aggression has been fueled in part by media reports of bull shark attacks, including the 1916 Jersey Shore shark attacks that inspired Jaws— both Peter Benchley’s novel and the 1975 blockbuster (although both actually feature a great white shark). Bull sharks are indeed responsible for many shark attacks near coastal shores, and they pack a ferocious bite. But the reality is more nuanced. “I always tell people that any animal, human or dog, we all have different personalities,” Lopez told Ars. “So you can get a bull shark that’s really aggressive, but you can also get one that’s not. Their main focus is always catching meals. But they’re not like, ‘Oh, I’m going to be aggressive with everyone. thing I see.'”
It wasn’t entirely clear from the various accounts whether it was really bull sharks that stole the fish, as it all happens underwater. So the first order of business for Gustafson and Lopez was to verify the anecdotal reports and try to catch a bull shark in the act. They used a fishing line camera to get a low-resolution shot of a bull shark stealing a hooked fish in just 20 seconds, but they had to go into the water to capture more footage with a 360-degree drop camera. A shark cage was fine, but most metal cages are fairly noisy in terms of sound reflection. That’s fine with some regional sharks used to the cages, according to Gustafson, but the Weiba bull shark population is more isolated and more likely to be spooked by the noise.
So Gustafson and Lopez turned to underwater cinematographer Colin Thrupp, who constructed a new noise-cancelling shark cage from polyethylene tubing with the joints welded via electrofusion welding. The plastic absorbs sound more than a metal cage, and the black color also means less reflective glare. The cage served its purpose; the bull sharks were cautious at first, but the camera eventually caught six or seven of them swimming nearby like a pack—unusual behavior for such a solitary and territorial species. “Part of our hypothesis is that this is a bull shark population that doesn’t really migrate much because they have warm water year round. It’s a nice tropical area,” Lopez said. “That may be one of the factors [providing] opportunity for socialization. They might get a little bit of tolerance between each other because they get an easy meal.”
The footage also showed a bull shark approaching the hooked fish slowly at first, waiting for it to tire of struggling, then biting the fish’s tail end and propeller before swinging back to gobble up the rest. This is a calm, intelligent hunting strategy, according to Gustafson and Lopez, the antithesis of the stereotypical mindless aggression commonly associated with bull sharks. In fact, it’s strikingly similar to the way killer whales – known for their intelligence – hunt, using a surgically precise approach to conserve energy. “Being an apex predator means you invest a lot of energy into all those catches,” Lopez said. “If that’s not accompanied by a reward, you’ll have less energy for the next chase. So they must be very intelligent [to determine] “Where am I putting my energy into all this?” Sometimes, when they’re not sure, they do these test bites.”
However, the plastic cage didn’t perform perfectly and started bouncing around and buckling as the swell developed and the underwater turbulence increased. The communications link to the surface also failed, resulting in some tense moments until the cage was brought back to the surface. “We were in that cage and it was gloomy and the current was huge,” Gustafson recalled. “Then we saw a cable tie fly past us and thought, ‘Oh, that’s not good,’ because they’re basically what holds the cage [mesh] together. Then another passed. Then the cage began to warp. It was like being in one [trash] compactor.”
Gustafson and Lopez also managed to tag several sharks with acoustic transmitters to track their movements. Since they had seen a young shark among the adults, they also found the most likely bull shark nursery in a nearby river, taking a biopsy from a baby shark for DNA analysis. After Thrupp repaired and strengthened the plastic shark cage, they deploy it a second time to take biopsies from two other sharks for comparison, using harpoon-like tools.
The results showed that the juvenile they biopsied upstream was half related to the female bull shark they biopsied in the ocean, while the third shark sampled was related to both. So all three sharks probably share an ancestor between them. This is further evidence that the population on Weiba doesn’t move much, as there’s more opportunity for interbreeding, especially since shark litters typically have multiple fathers, according to Gustafson.
The next step involves collecting more DNA samples from the Weiba bull shark population to expand the genetic analysis, as well as tagging and tracking more bull sharks to get a sense of their movement patterns to determine how the top of the gulf ecosystem (Weiba) connects to the western and eastern sides of the continent. “Are they going all the way to Perth in the west or all the way to Sydney?” Gustafson said. “Tortoises usually come back to the same beach where they were born. We think these bull sharks are starting to do the same kind of thing. But we don’t know if they’re coming back to the same river they were on.” born in, or in the same area in which they were born.”
More data should also give them a better idea of the size of the bull shark population in Weiba, as the popular perception among fishermen is that it must number in the hundreds or thousands. And as fishermen continue to lose their catches, there is a greater risk that more anger will be directed at the bull sharks, leading to less support for their conservation and more calls to cull the population. (The species is listed as Vulnerable on the IUCN Red List.)
“The more time you spend in the water, the more likely you are to encounter a shark,” Lopez said. “But that’s just because you spend more time in the water fishing. It doesn’t mean there are more sharks lurking in the water and being aggressive. It’s important to make these documentaries because you’re never going to fool people change your mind.” if you just say sharks aren’t bad. You have to include them in a little bit of science, lay it out. For projects like this we go there and spend time in the pubs talking to the fishermen. We even had some fishermen help us take samples.”
Bull Shark bandits streaming now on Disney+ and Hulu and premiering on NatGeo WILD on July 25, 2023.