By DIVE Staff
Researchers were baffled by a strange behaviour they kept witnessing in a group of Sydney common octopuses they were studying in Jervis Bay, Australia. Repeatedly the octopus would gather up a pile of debris and then using their siphons squirt the muck at another octopus.
The blasts were as if they were deliberately ‘throwing’ missiles at each other – a behaviour previously only ever record among mammals.
Then they saw that one of the attackers was a female and she was ‘throwing’ armfuls of silt at a male who had been trying to mate with her.
The behaviour was recorded by scientists led by Professor Peter Godfrey-Smith of Sydney University and author of the highly acclaimed book Other Minds: The Octopus, the Sea, and the Deep Origins of Consciousness.
He said: ‘We were surprised to see the behaviour, and have spent a long time trying to work it out.
One of the clues to the nature of the behaviour is that the aggressor tends to change skin colour to a darker tone before an attack. The researchers have already established that changing colour to a darker tone is a sign of aggression. They have recorded octopuses chasing away other octopuses and evicting them from their burrows – the aggressor often takes on a far darker skin colour before an attack.
‘The throwing – or propelling, or projecting – of objects that have been gathered and held is rare in the animal kingdom. To propel an object, even for a short distance, underwater is especially unusual, and also quite hard to do,’ said Professor Godfrey-Smith
Writing this week in the journal Plos One, Godfrey-Smith and colleagues report how in 2015 they recorded more than 21 hours of video in Jervis Bay off the south coast of New South Wales using underwater stationary cameras, capturing the behaviour of about 10 octopuses.
In total, they recorded 102 throws and more than 90 per cent turned out to be by females. Half of the attacks occurred when the octopuses were interacting often during mating attempts. Other ‘throwing’ attacks were directed at the stationary remote cameras.
The attacks seem to be designed to warn off advancing males who often duck and sometimes rush off in the other direction.
The group of octopuses in Jervis Bay are unusual in that they gather in one place – most of the time octopuses are solitary animals.
