For the first time, dolphins have been caught on camera raising their heads out of the water while holding an octopus and slamming it against the ocean's surface.
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Biologists at Murdoch university have released a paper in Marine Mammal Science, revealing a fascinating but brutal aspect of the relationship between bottlenose dolphins and octopus. It's been called 'octopus-handling'.
The process involves the dolphin carrying an octopus to the ocean's surface and then throwing it around in a bid to break the animal apart.
"Bottlenose dolphins are highly social animals, however there is no evidence that this behaviour is co-operative," lead author of the paper Kate Sprogis, tells WIRED. "We observed ‘octopus handling’ when dolphin groups were travelling, foraging and socialising- so all different behaviours."
The complexities of predator / prey dynamics have been well documented within the animal kingdom. Each species has its preferred method - alligators and crocodiles have the spinning death roll, Australian fur seals throw large fish up into the air before consuming them. These methods of prey preparation are all dictated by the size and strength of the animal in question. When looking at the relationship between the bottlenose dolphin and the octopus, you might think that the odds would be firmly in favour of the dolphin. But the truth is far more complicated.
Having studied these behaviours since 2007 in southwest Australia, Kate Sprogis and her colleagues observed 45 octopus tossing/shaking events over the period. This process occurred in two parts - first, a dolphin would shake an octopus trapped within its jaws, forcefully hitting it against the surface of the water. Secondly, the dolphins would toss their prey across the water - particularly if parts of the octopus had fallen off during the original shaking process. These octopus handling events could last from one to six minutes.
This type of behaviour has never before been documented in dolphins and the Murdoch team speculate that it could be due to the octopus' complex reflexive behaviour. Firstly, the process is to remove the octopus head and mantle, to "tenderise and ensure the arms are inactive" and to break the octopus up into smaller parts for consumption.
The team recorded one adult dolphin that had choked to death on a large 2.1kg octopus. Another dolphin had suffered a similar fate, asphyxiating with an octopus in its stomach, its arms and legs still stretching up from its throat and out of its mouth.
Octopus arms can continue to react to stimuli even after death - in instances where the arms have been completely detached from the head.
This could explain why octopus handling occurs more frequently in winter and spring, when temperature reach around 18C - coinciding with octopus mating cycles. Octopus are semelparous, meaning that once males mate and females lay eggs, they become senescent until their death. With uncoordinated movements and a deteriorating physical condition, octopus during this period are far easier prey for dolphins.
"Octopus handling appears to be an opportunistic event," Sprogis says. "Other species of whales and dolphins feed on octopus, as cephalopods (octopus, squid) are high in nutrition. We suggest that dolphins are feeding on the octopus as a prey source, and they may be gaining nutrients that they may not be obtaining from other prey sources."
This article was originally published by WIRED UK
