Weipa is a small coastal mining city in Queensland, situated in northeastern Australia, notably favored by sports activities fisherman due to its annual competitors, the Weipa Fishing Basic. However lately, fishermen have reported an growing variety of incidents the place native bull sharks are pulling off audacious underwater raids, actually ready till a fish is hooked and chomping it off the road. Some fisherman estimate they’ll lose as a lot as 70 p.c of their catch to the sharks, which appear to particularly goal fishing boats.
(Some spoilers for the documentary under the gallery.)
It is atypical conduct for bull sharks and it raises an fascinating query: is that this proof that this species of shark—identified (a bit unfairly) within the well-liked creativeness for being aggressive “senseless killers”—are extra clever than beforehand assumed? That is one of many questions that shark biologists Johan Gustafson and Mariel Acquainted Lopez got down to reply, and their preliminary discipline work has been documented for posterity in Bull Shark Bandits, a part of Nationwide Geographic’s 2023 SHARKFEST programming. SHARKFEST is 4 full weeks of “explosive, hair-raising and celebratory shark programming that … showcase the charming science, energy and wonder of those magnificent animals,” per the official description.
The fish-stealing conduct is technically generally known as depredation. Amongst different components, Australian fish shares have decreased by greater than 30 p.c over the past decade, and the sharks look like adapting accordingly and educating the conduct to their fellow sharks.
“Many alternative species do it, together with dolphins and orcas, excessive stage predators, however shark depredation particularly is happening throughout Australia in the meanwhile,” Gustafson informed Ars. “In areas the place there is a increased fishing stress, the conduct is happening extra usually or extra intensely. We name it habituation. They’ve discovered a behavior, they really be taught off one another, they usually unfold it round [the population].”
Bull sharks (Carcharhinus leucas) are discovered all around the world, normally preferring heat, shallow, coastal waters and freshwater rivers. They don’t seem to be a real freshwater species, however the females usually start their pups upriver since such spots present a extra protecting surroundings for nurseries. (Sharks do not rear their younger; child sharks usually be part of the grownup ocean inhabitants once they attain about eight years of age.) Bull sharks normally develop to a median of seven ft (for males) and eight ft lengthy (for females), and their highly effective chunk can generate as a lot as 1330 kilos of power (5914 newtons).
Bull sharks are thought-about opportunistic feeders, that means they eat in brief burts and digest for longer intervals throughout occasions of shortage. Their food regimen favors bony fish and smaller sharks (together with their fellow bull sharks), in addition to turtles, birds, dolphins and crustaceans. They’re additionally pretty territorial and solitary, preferring to hunt alone or sometimes in pairs.
Their repute for aggression has been fueled partially by media reviews of bull shark assaults, together with the 1916 Jersey Shore shark assaults that impressed Jaws—each the novel by Peter Benchley and the 1975 blockbuster movie (though each truly featured a Nice White shark). Bull sharks are certainly answerable for many shark assaults close to coastal shores, they usually have a ferocious chunk. However the actuality is extra nuanced. “I all the time inform individuals that each animal, each human or each canine, all of us have completely different personalities,” Lopez informed Ars. “So that you would possibly get a bull shark that’s actually aggressive, however you would possibly get one that’s not. Their fundamental focus is all the time catching meals. However they don’t seem to be, like, ‘Oh, I’ll be aggressive to each single factor that I see.'”
It wasn’t completely clear from the varied accounts if it actually was bull sharks stealing the fish, because it all occurs underwater. So the primary order of enterprise for Gustafson and Lopez was to confirm the anecdotal reviews and attempt to catch a bull shark within the act. They used a fishing line digicam to seize a low-resolution shot of a bull shark stealing a hooked fish in simply 20 seconds, however they wanted to get into the water to seize extra footage with a 360-degree drop digicam. A shark cage was so as, however most metallic cages are pretty noisy by way of sound reflection. That is high quality with some regional sharks who’re used to the cages, per Gustafson, however the Weiba bull shark inhabitants is extra remoted and extra more likely to be spooked by the noise.
So Gustafson and Lopez turned to underwater cinematographer Colin Thrupp, who constructed a novel noise-cancelling shark cage out of polyethylene pipe with the joints welded through electro-fusion welding. The plastic absorbs sound greater than a metallic cage, and the black colour additionally means much less reflective shine. The cage served its function; the bull sharks have been initially cautious however the digicam finally caught six or seven of them swimming close by as a pack—uncommon conduct for a such a solitary and territorial species. “A part of our speculation is that it is a inhabitants of bull sharks that do not actually migrate that a lot, as a result of they have heat water situations all yr spherical, it is a good tropical space,” mentioned Lopez. “That’s possibly one of many components [providing] alternative for socialization. They may be getting a little bit of toleration between one another as a result of they’re getting a straightforward meal.”
The footage additionally confirmed a bull shark approaching the hooked fish slowly at first, ready for it to get uninterested in struggling, after which biting off the fish’s tail finish and propeller, earlier than swinging again round to gulp down the remainder. This can be a calm, clever looking technique, per Gustafson and Lopez, the antithesis of the stereotypical senseless aggression normally related to bull sharks. The truth is, it is strikingly just like how killer whales—identified for his or her intelligence—hunt, using a surgically exact strategy to save lots of power. “Being a high predator means you make investments lots of power in all these catches,” mentioned Lopez. “If that does not include a reward, you will have much less power for the following chase. So that they need to be very clever [to determine] ‘The place do I put my power in all this?’ Generally, once they’re undecided, they do these check bites.”
The plastic cage did not carry out completely, nevertheless, beginning to bounce round and buckle as swells developed and underwater turbulence elevated. The communications hyperlink to the floor additionally went out, leading to some tense moments till the cage was introduced again to the floor. “We have been in that cage and it was gloomy and the present was large,” Gustafson recalled. “Then we noticed a cable tie fly previous us and thought, ‘Oh, that is not good,’ as a result of they’re truly what’s holding the cage [mesh] collectively. Then one other one glided by. Then the cage began to deform. It was like being in a [trash] compactor.”
Gustafson and Lopez additionally managed to tag a number of sharks with acoustic transmitters to trace their actions. Since they’d noticed a juvenile shark among the many adults, additionally they situated the almost certainly bull shark nursery in a close-by river, taking a biopsy from one child shark for DNA evaluation. As soon as Thrupp had repaired and strengthened the plastic shark cage, they deployed it a second time to take biopsies of two different sharks for comparability, utilizing harpoon-like instruments.
The outcomes confirmed that the juvenile they biopsied upriver was half-related to the feminine bull shark they biopsied again within the ocean, whereas the third sampled shark was associated to each of them. So all three sharks possible share an ancenstor between them. That is but extra proof that the inhabitants at Weiba is not transferring round a lot, as a result of there may be extra alternative for interbreeding, notably since shark litters usually have a number of fathers, per Gustafson.
The following step consists of gathering extra DNA samples from the Weiba bull shark inhabitants to develop the genetic evaluation, in addition to tagging and monitoring extra bull sharks to get a way of their motion patterns with the intention to decide how the highest finish of the gulf ecosystem (Weiba) connects to the western and jap sides of the continent. “Do they go all the way in which right down to Perth on the west or proper right down to Sydney?” mentioned Gustafson. “Turtles have a tendency to return again to the identical seaside the place they have been born. We expect these bull sharks are beginning to do the identical type of a factor. However we do not know in the event that they’re coming again to the identical river that they have been born in, or into the identical space that they have been born in.”
Extra information also needs to give them a greater concept of the dimensions of the bull shark inhabitants in Weiba, for the reason that well-liked notion amongst fishermen is that there should be a whole lot or 1000’s of them. And as fishermen hold dropping their catches, there’s a better threat of extra anger being directed on the bull sharks, resulting in decreased assist for his or her conservation and extra requires culling the inhabitants. (The species is listed as weak on the IUCN Purple Record.)
“The extra you spend time within the water, the likelihood that you’ll encounter a shark turns into better,” mentioned Lopez. “However that’s simply since you’re spending extra time within the water fishing. It does not imply there are extra sharks lurking within the waters and being aggressive. It is essential to do these documentaries since you’ll by no means change the thoughts of individuals should you simply say sharks aren’t unhealthy. You could embrace them in somewhat little bit of the science, clarify it. For tasks like this, we go up there and spend time on the pubs speaking to the fishermen. We have even acquired some fishermen serving to us take samples.”
Bull Shark Bandits is now streaming on Disney+ and Hulu, premiering on NatGeo WILD on July 25, 2023.