Daughter of the sea - Berlie Doherty

Janet and her husband live on a wild island where life is dominated by the sea. They long for a child and take a little girl rescued from the sea into their home. A strange man comes from the sea to reclaim Gioga, but Janet hides her for she is now like a daughter to her. He returns and Janet shoots and kills him but, instead of a human body, a seal is left dead on the beach. All the seals then leave the island and the islanders realise that Gioga must be returned to the sea and this, after much hardship, is what happens.