Cuttlefish is often thought to be a lonely cephalopod. New footage shows that wild cuttlefish form shoals in order to migrate. This suggests they are much more social than we thought.
The animal kingdom is familiar with grouping. It provides a variety of benefits, including the ability to forage, fight off predators, and meet mates. Cephalopods are most familiar with the behavior of cephalopods. Squids form large schools of thousands. Cuttlefish, much like octopuses prefer to explore the world by themselves and social behavior is rare among them.
Christian Drerup from the University of Cambridge, and Gavan Cooke from The Cephalopod Citizen Science Project collected a series of photos and videos of divers who dived in waters off the UK's south coast. They found 10 instances of European cuttlefish (Sepia officinalis) shoaling.
Cooke says that the literature is quite rigid about cephalopod behavior and that you can accept it until you actually see them.
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The videos show cuttlefish moving together in various formations. Some are in large groups of 30. Sometimes they made a horizontal line with one cuttlefish facing in the opposite direction, possibly as a guard or to sleep while the rest of the group slept. Sometimes, the cuttlefish formed a spherical shape facing outwards, much like an ancient Roman army testudo formation. Sometimes, the cuttlefish would drift apart and then return to a group structure.
These observations were made in August and September 2013, when the cuttlefish migrate from their nursery grounds on the coast towards deeper waters off the northern coast of France. Cooke says that shoaling provides a means of selfish herd defense, protecting the cuttlefish from a variety of predators. It may also improve navigation and offer the possibility of social learning.
Journal reference: Ethology DOI: 10.111/eth.13226
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