'Carpet' on ocean floor: scientists stumble upon thousands of sleeping sharks

Scientists have spotted thousands of sharks napping on the ocean floor. This discovery has confused experts, as they cannot explain why there are only females.

Scientists had previously seen them in this location six years ago - during the first survey of the Beagle Marine Park in Bass Strait off the coast of Victoria, Australia. This species of shark is called Port Jackson sharks, and they are known for their somewhat bizarre appearance, with two prominent ridges running from their blunt noses to the backs of their heads, The Sun writes.

These sharks can grow to about 1.65 meters in length. They are nocturnal, so they tend to sleep during the day and hunt squid, octopus and crustaceans at night. Unlike many other shark species, Port Jackson sharks are not considered an endangered species.

Port Jackson's mysterious sleepy collection of sharks has now been found again using an underwater robot aboard a South Australian Research and Development Institute (SARDI) research vessel.

Dr. Giacumo Monk from the University of Tasmania's Institute of Marine and Antarctic Research said the sharks were tightly bunched together like a carpet spread out on the seabed.

"We were hoping to see sharks again during this survey. But coming across them twice in a 3,000 square meter park is like finding a needle in a haystack," explained the trip leader.

So when the scientists crossed the reef rise and saw the sharks napping at a depth of 65 meters beneath the vessel almost exactly where they had been six years earlier, they were amazed.

Port Jackson sharks are known to mate in late winter - they have a distinctive spiral egg shell that they lay on the reef for protection. However, scientists can't explain why only females are here. They speculate that perhaps they are coming here to prepare themselves before moving on to the areas where they normally lay their eggs.

"We now have more questions than answers, but we do know that the males and females of this species often live separately except for mating," Dr. Monk said.

"We don't know exactly why there are only females here. Perhaps they are dabbling in a local delicacy - sea combs - before the long journey north to lay eggs. However, the fact that we came across them again suggests that this area is important to them," the scientist adds.

Port Jackson sharks do not pose a threat to humans. Even in very rare cases they do bite, the worst that happens is a bruise and a torn wetsuit.

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