Mysterious detail in shark footage stumps scientists
The discovery of thousands of sharks sleeping together has raised more questions than it answers.
A “mysterious” gathering of sharks on the ocean floor off Australia’s south coast has baffled scientists. Footage taken by an underwater robot shows thousands of sharks "tightly packed" together as they sleep.
The Port Jackson sharks were found in exactly the same place within the 3,000-square-kilometre Beagle Marine Park in Bass Strait. But there was a strange detail experts noticed that they’d missed when they surveyed the area six years ago.
"One of the really interesting things that we were able to discover this time around is it looks like an aggregation site of mainly females. We didn't see any males. Which poses more questions than answers for us,” underwater imagery expert Dr Jacquomo Monk said.
Monk is the leader of a team from University of Tasmania Institute for Marine and Antarctic Studies (IMAS), which is working with the South Australian Research and Development Institute (SARDI) to survey central Bass Strait with a remote controlled ocean vehicle. The project is designed to provide information to the park's managers so they can ensure the species that live there are being properly protected.
“A spectacular scene was relayed to us by a remotely operated vehicle equipped with seven cameras… There were thousands of sharks tightly packed like a carpet spread across the seafloor,” Monk added.
You can see the sharks in the video below.
Why are the sharks all in one place?
While it’s known that the sexes live apart except for when they’re mating, what’s drawing females to this specific location remains a puzzle. But the team suspects they could be gathering in preparation to mate, or its possible there’s a food source nearby that’s important to the population as it migrates north for egg-laying.
“Seeing them again does tell us that the area is important to them,” Monk added.
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People living in NSW and Victoria are probably familiar with Port Jackson sharks, but they're normally just seen in smaller groups, of two to five. So seeing so many within just a few hundred metres was something Monk described as "really quite special".
If you haven't seen a Port Jackson shark up close, you've probably seen one of their distinctive spiral-shaped eggs. Once the egg is laid, the mother will take it in her mouth and screw it into a crevice between rocks.
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