What Could Trigger a Shark Attack? | Rogue Shark

Across the Whit Sundays, hundreds of baited cameras are deployed and listening stations fixed as scientists race to understand why these previously safe waters have turned deadly.

As the footage comes in, one big clue emerges: the poor visibility. What we have here is a satellite image of the actual water clarity of the Whitsundays area. It's showing the turbid waters versus the clearer waters, and as you can see, most of the Whitsundays region itself is quite turbid, including Sid Harbour. Here, you don't get the bluer waters, so you move offshore. These turbid waters are probably driven by the actual sediments coming off the land and out of these river systems.

Now, the interesting thing about these river systems is that these are pretty key habitats for bull sharks. In the last 20 years, bull sharks have been responsible for five attacks in Australian waters. Armed with an incredible sense of smell and a sixth sense that allows them to detect vibrations in the water, they're perfectly adapted for hunting in murky conditions. But without vision, they can make mistakes. Most shark bites are cases of mistaken identity.

"If you live in an environment where you can't see very well, you have to be very, very quick and very decisive," a scientist explains. "So they'll bite quickly and sort of ask questions later." This is consistent with at least the first bite in Sid Harbour. This is one bite that's removed a chunk of flesh in one fell swoop. If I was a betting person, I would lean towards this being inflicted by a [incomplete point of view] on the Australian mainland.

Richard and Adam's colleague, Andrew Chin, is following a different line of inquiry. He's trying to discover why these previously safe waters might have turned so deadly. "What we were looking for was the perceptions of people who had been to the Whit Sundays over the years to understand what sort of things had they seen. What did they think was happening in some of these different anchorages like Sid Harbour? Was there anything that people were doing that could explain what might have just happened?"

"When we have a look at the data, it's obvious that Sid Harbour is a very busy place," Andrew continues. "There's a lot of people anchoring in, there's a lot of activities going on there. People are paddle boarding, people are swimming, so you've got a lot of waterboard activity. You also have people discarding rubbish, throwing food scraps over the side. Some people are even fishing or baiting in these anchorages. Those two activities don't go hand in hand."

"Sharks are smart; they will learn. They're not going to waste energy swimming around the whole ocean looking for food when you can get it delivered to you off the side of a boat." Throwing food waste overboard is illegal in Whitsunday waters, but the team unearths evidence that the practice continues.

"Could this be triggering the attacks? It definitely was a turning point. You start putting two and two together of like, hey, these people are jumping off a boat or falling off a paddleboard and getting bit straight away, and there's reports of lots of food going in the water, lots of boats."

"If you imagine being a shark in that situation, you're cruising around, there's food scraps around in the water. Smell can drift for long, long distances as well, so they could be following that upcurrent to its source, thinking what's happening here. As more scraps go in the water, then they can feel the commotion of little bait fish zipping around, going for a feed and all that kind of stuff. So there's a lot of stimulus in the water."

"When they switch into feeding mode, they're like a bit more on edge and they, you know, okay, where is this? Where is this? I'm trying to find the source, trying to find the source. The visibility is bad; can't really see around. There's a huge shadow above me, but something's under it, and then splash! Oh cool, I'm gonna go for it. And unfortunately, if it's a person that's jumped in at that stage, they will come through at high speed and bite."

The possibility that human activity could trigger the attacks is new and alarming. It has implications for every bay around the world where boats gather in large numbers, particularly locations in Southern Florida.

"The other thing that a boat does," Andrew explains, "is it provides you with a hiding spot, right? So you have this big thing of shade that hangs over you with structure. It's kind of like a movable ambush point for a shark. It's interesting that many of the shark bite accounts that we have— not just in Sid Harbour, but everywhere—people have been bitten when they've jumped into the water with a splash and then they've been struck."