Selective filter feeder that orients itself towards the most productive zooplankton patches, preferring areas where zooplankton density is above 1 g/m3 (Ref. 88781). Occurrence and movements appear to be correlated to sea surface temperature, in particular to the thermal boundaries at tidal and shelf-break fronts (as these areas may have seasonally productive zooplankton patches which the shark locates and utilizes) (Ref. 50200, 88781, 88826). Often in close association with shoals of other fish such as Clupea harengus and Scomber scombrus in the Northern Atlantic (Ref. 310). During the summer months the basking shark is often seen swimming slowly near the surface with its large mouth held open for approximately 30 to 60 seconds. Water passively enters its mouth, possesses long bristly gill rakers on long gill arches to filter out the zooplankton. It periodically closes its mouth and forcefully constricts its gill arches, probably as a means to expel as much water from the buccal cavitiy (Ref. 33579). On average, about half a tonne of plankton may be found in an individuals stomach (Ref. 43278). During the winter months found to inhabit the deeper waters of the shelf and shelf edges of the northeast Atlantic (Ref. 50200), the winter diving behaviour may be related to the search for discrete calanoid patches at deeper depths (Ref. 50200).