Observations of schooling behaviour in the oval squid Sepioteuthis lessoniana in coastal waters of Okinawa Island

Cuttlefish can school in the field

“…From the recorded videos, we determined the numbers of members within a group in the area for each observed occasion (>10 s), and then also calculated the number of occasions each size of group was encountered, and the duration of these encounters. The shapes of the groups in S. latimanus were described in a geometric configuration, following the methods used in fish (Partridge et al 1980;Hemelrijk et al 2010) and Sepioteuthis (Moynihan and Rodaniche 1982;Boal and Gonzalez 1998;Adamo and Weichelt 1999;Sugimoto et al 2013). Outlines and dimensional measures, such as areas or lengths, of each shape of the groups were estimated by connecting members with lines.…”

“…In cases when a member began to separate from the group and subsequently the remaining members in the group followed it, we judged this as 'following behaviour' and counted the number of occurrences. Following behaviour is one of the characteristics of schools of fish (Krause et al 2000) and Sepioteuthis (Moynihan and Rodaniche 1982;Sugimoto et al 2013). Furthermore, we recorded body patterns, such as texture, posture, and colouration of the body, in accordance with Hanlon and Messenger (1988).…”

“…To reveal the structures of S. latimanus groups, within groups we calculated neighbour distance (ND), the nearest neighbour distance (NND), nearest neighbour angle (NNA), and the percentage of the nearest neighbour looking in the same direction, as these criteria are used during evaluation of group structures in fish (Pitcher and Wyche 1983) and Teuthoidea schools (Hurley 1978;Boal and Gonzalez 1998;Adamo and Weichelt 1999;Sugimoto and Ikeda 2012;Sugimoto et al 2013). As was done in these past studies (Pitcher and Wyche 1983;Boal and Gonzalez 1998;Adamo and Weichelt 1999;Sugimoto and Ikeda 2012;Sugimoto et al 2013), we defined 'neighbours' as members positioned alongside each other inside of a group.…”

“…For example, the California market squid Doryteuthis opalescens, the Caribbean reef squid Sepioteuthis sepioidea, and the oval squid Sepioteuthis lessoniana form schools consisting of 10-100 individuals (Moynihan and Rodaniche 1982;Adamo and Weichelt 1999;Hunt et al 2000;Sugimoto et al 2013). Schools of D. opalescens are composed of individuals of the same approximate body size (Hurley 1978), while schools of S. sepioidea and S. lessoniana usually contain large and small individuals of both sexes and maturation stages (Moynihan and Rodaniche 1982;Hanlon and Messenger 1996;Sugimoto et al 2013). It is believed from the composition of the schools that young S. sepioidea may acquire many different kinds of information by watching and following individuals, especially larger squid (Moynihan and Rodaniche 1982).…”

“…It is believed from the composition of the schools that young S. sepioidea may acquire many different kinds of information by watching and following individuals, especially larger squid (Moynihan and Rodaniche 1982). Additionally, schools of S. sepioidea and S. lessoniana form shapes of ragged-lines, spheres or sheets (Moynihan and Rodaniche 1982;Boal and Gonzalez 1998;Adamo and Weichelt 1999;Sugimoto et al 2013). In schools of S. sepioidea, almost all individuals arrange themselves by facing in the same direction; however, some individuals face in the opposite direction, acting as sentinels (Moynihan and Rodaniche 1982;Hanlon and Messenger 1996).…”