Photo Renaud de Stephanis

Mother and calf in the Strait of Gibraltar

Killer whales have strong social bonds within their group that are of a matriarchal type: the females stay together their entire life while males leave the maternal group at the adult stage to go reproduce with other groups. The size of groups varies from 5-6 to around thirty individuals. The sighting of a gathering of a hundred animals is probably the result of a temporary coalition of many groups.

Killer whale diets vary depending on the population. Some of them prefer fish like herrings or salmon while others feed mainly on marine mammals like porpoises, sea lions or even whales. Killer whales have hunting techniques adapted to each of their prey. The most impressing one is the voluntary stranding on beaches to catch elephant seals in Crozet Island or sea lions in Patagonia.

Gestation lasts one year. The calves are generally born in autumn and winter. They stay dependant on their mothers and other females of the group for more than one year. They learn different hunting techniques and the dialect characteristic of each population, or even to each group within a population. We consider that there is a true transmission of culture through generations.

Problems of interactions with fisheries are more and more worrisome because fishermen do not hesitate to kill the killer whales preying on their fishes. Some populations see their numbers seriously decreasing; it is the case in Crozet (see article here) and probably also in the Strait of Gibraltar. Only long-term researches can bring sustainable and beneficial solutions for everybody. We are working on it!