Dietary variations and specializations of killer whales (Orcinus orca) in Norway

Killer whale groups may adopt remarkably specialized diets, feeding only on a small subset of available prey. Because variations in feeding habits may have implications for the conservation of this species, it is important to account for heterogeneity in diet. Killer whales in Norway have mainly been studied at the seasonal grounds of their main food source, the Norwegian Spring Spawning herring. Other prey types have also been sporadically recorded, implying a diversified diet, but dietary patterns at the individual level had not been investigated to date. In her doctoral thesis, Eve Jourdain used six years of year-round field observations to identify dietary habits of individual killer whales in northern Norway. Chemical tracers were further used to conclude on the recurrence of these dietary habits. She concluded that killer whale groups adopted different diets with various levels of prey specialization. Importantly, there was a segregation between groups that were fish-specialists throughout the year, and others that fed on seals in addition to fish. Seal-eating groups had higher pollution levels in their tissues than fish-eaters, leading to possible variations in individuals’ health status. Future research should investigate these variations, and how they may impact the population as a whole