Killer Whales (Orcinus orca) were observed on 4 August 2012 attacking Belugas (Delphinapterus leucas) at high tide near the mouth of the Seal River (59°9T9"N, 94°45'28"W) in southwest Hudson Bay, near the location where six Belugas had been fitted with satellite transmitters three weeks earlier. The distribution of Belugas was analyzed before, during, and after the attack. In the presence of Killer Whales, the six Belugas altered their behaviour by reducing their combined range size from 285 km2 four days before the attack to 172 km2 on the day of the attack. Their range more than tripled, to 655 km2, in the days immediately following the attack before returning to the pre-attack size. Following the attack, the tagged Belugas expanded their range northward, going from a mean pre-attack distance of 9.4 km from the attack site to a maximum of 23.5 km. Visual observations of Belugas clumping together and moving toward shore corroborated satellite data. This evasive behaviour by Belugas was different from that reported for Narwhals (Monodon monoceros) suggesting that the two monodontid species may have evolved different survival strategies related to the risk of Killer Whale predation. With predicted changes to Arctic sea ice, the summering habitat of Belugas will be available to their main predator for longer periods. A better understanding of Beluga behaviour and risk of predation is required for Beluga conservation and stock management. [ABSTRACT FROM AUTHOR]