A small detail in drone video captured in shallow waters off the Australian coast has sparked dozens of theories. The footage shows a large dark-coloured shark with another fish about half its size swimming in tandem off Queensland's Bribie Island.
There was an incredible response after Doug Bazley uploaded the 47-second clip to his Bluey's Photography social media page, with hundreds of fishermen commenting. Several respondents thought both creatures had been hooked on the same line and were being reeled in. Another joked the fish might believe it's a shark.
While others thought the fish might be completing a smart survival manoeuvre to stay away from the shark's gaping jaws. "Keep your friends close, and your enemies closer," one wrote.
Because of the closeness of the pair, Bazley was initially deceived into thinking he was watching a great white shark.
"Every now and then, you see this big white, shiny thing underneath. I thought it was the belly, but it was actually another fish," he told Yahoo News.
The species in the video is likely a bull shark being followed by a pelagic fish, potentially a trevally, according to Dr Adam Smith, an adjunct professor with James Cook University and the CEO of marine ecosystem consultancy Reef Ecologic.
While encounters between the two are seldom observed by swimmers, the behaviour is well-known to experts.
"Big sharks are a bit like an island. There are species that hang around them, whether it's remoras, pilot fish, or cobia," Smith explained to Yahoo.
"They either follow them for an advantage, to pick on the scraps of their feed, or to avoid predation. And it might be for a short time, or it might be for a long time."
Because it makes sense to be behind a predator, rather than in front, similar behaviours have also been seen in fish following seals and great whites.