text: Rescuers managed to return three other beached whales to the sea.
  Fire crews sprayed the whales with seawater as local teams tried to return them to the sea.
  Expert Jacky Karpouzopoulos, of the Centre for Marine Mammal Research at La Rochelle, said the beaching may have followed the death of a dominant male in the pod.
  He told La Voix du Nord newspaper that the whales could have been one family of which the dominant male died at sea and the others followed his body to the shore.
  "The group was in the middle of a deep-sea migration towards the Faroe Islands to reproduce and feed," he said.
  Mr Karpouzopoulos described the beaching of so many whales as "exceptional".
  About 400 local residents went to the beach to try to help the rescue operation, La Voix du Nord reported.
  It said that two of the rescued whales stayed close to the shore, as if waiting for the others to be returned.
  The largest of the dead whales was a male more than 5m (16ft) long.
  Autopsies will be carried out at the University of Liege to determine the cause of death.
target: Seven pilot whales have died after being found stranded on a beach at the northern French port of Calais.