<I>In situ</I> observations on behaviour of the ommastrephid squid genus <I>Illex</I> (Cephalopoda: Ommastrephidae) in the northwestern Atlantic

Abstract

We compiled observations of ommastrephid squid of the genus Illex, primarily Illex illecebrosus from archived submarine video footage recorded during dives off Cape Hatteras and New England, and in the Gulf of Mexico. Based on the behaviour observed, we derived a partial in situ ethogram, or catalogue of the body patterns and behaviour. In total, 36 components were observed: 16 chromatic components (5 light and 11 dark), 10 postural components and 10 locomotor components. Co-occurrence analyses were used to show that specific sets of components occurred together either more or less often than they would if chosen at random. In addition, some of the components were observed occurring during specific behaviours, such as bottom sitting, hunting, or schooling. Such observations by submersibles also provide very precise, although incomplete, records of depth distribution. We summarize the depths and altitudes above bottom of these observations by time of day. Most of the squid were observed near bottom at depths of about 200-900m. The deepest depths observed were during daytime and the shallowest during the evening. However, individuals were observed as much as 1000m above the bottom during daytime whereas others were on or near the bottom in deep water during the evening.