Cuttlefish can school in the field

Cuttlefish (Sepiidae) are usually solitary in nature, but we have found evidence that the broadclub cuttlefish (Sepia latimanus) forms schools. S. latimanus groups of various sizes were observed for 145 min in Okinawa, Japan. The groups were comprised of 2-9 members that were usually of similar body sizes. The groups continuously changed shape, forming either clusters or lines. The groups were regarded as schools and had characteristic structures such as synchronized and polarized swimming with similar distances apart from each other (similar to 4.0 mantle length), and swam in parallel (under 20A degrees or over 110A degrees in angle) to their nearest neighbours, regardless of the numbers of members in the group. Small members sometimes followed larger members within the school. These characteristics were similar to those observed in schools of Teuthoidea squid. Schools comprising large numbers of members frequently exhibited hunting behaviour for small crustaceans and fish. This is the first observation of schooling behaviour in wild Sepiidae.