Data related to Antarctic krill activity monitoring studies conducted in the Southern Ocean and South Atlantic during the Discovery 2010 cruise (JR177), 2007-2008. The activity monitor is a purpose-built apparatus for the observation of vertical migration patterns. Lighting within the apparatus is adjusted to that experienced by the krill at normal daytime depths and the temperature in the cool-room kept at the level of the seawater supply. The movements of the krill over a 10-day period were recorded - 5 days recording their vertical migration patterns under normal lighting conditions followed by 5 days in total darkness to see whether the activity pattern is maintained, indicating control by an endogenous circadian rhythm. Three runs were carried out, using animals from 60.44 S, 59.66 S and 52.75 S. Behaviour in many organisms (including krill) is strongly influenced by diurnal and seasonal changes in the environment. The evolution of circadian clocks has afforded organisms regulation of molecular and physiological rhythms, which in turn affect the animals'' rhythmic behaviour.