Killer whales in the North Sea are changing their habits to adapt to climate change.

The aquatic mammals have had to follow the migration of their favourite food: herring.

Herring populations have moved 300 km north of former breeding grounds in search of colder waters.

The clear and calm waters of Reisafjorden, in Norway's Far North, have in recent years become the winter playground of the Scandinavian country's killer whale population.

At three degrees Celsius (37 Fahrenheit), the cold water is perfect for the herring which, ahead of the spawning season in February and March, have fattened up and make a tasty dish for the hungry killer whales.