Coordinated nocturnal behavior of foraging jumbo squid Dosidicus gigas

Abstract

We used split-beam acoustic techniques to observe free-swimming of jumbo squid Dosidicus gigas during 4 cruises in the Gulf of California. Four-dimensional spatio-temporal data revealed that at night in shallow water, jumbo squid were using ascending, spiral-like swimming paths to emerge from extremely dense aggregations, and were likely foraging on potential prey that were found overlapping in depth with their tracks. Within small regions at the vertices of these swimming paths, individual squid swam back and forth repetitively before continuing their ascent. The behaviors observed in these high-use regions, described using density kernel statis- tics, are consistent with other observations of prey capture behavior by squid. Often, the observed swimming paths of individual squid were found to parallel those of other squid in depth over time. In addition to being coordinated in depth, movements of individuals within a group of up to 40 individuals were coordinated in horizontal space so that high-use areas were overlapping in hor- izontal space but separated vertically. The resulting groups of tracks look like interwoven multiple helices anchored at their vertices by bouts of presumed feeding. These highly polarized, complex, coordinated movement patterns constitute schooling. Polarization in these groups did not break down during apparent feeding events as has been observed in other species. In fact, the feeding events themselves may define the anchor for group behavior. Schooling of jumbo squid school will likely be critical in understanding many aspects of their biology.