Possible Clues:

• Hurried over to find most of whale, tusked whale
• Animal with large spiral tusk
• How to warn Henry to a whale of an extent
• Marine mammal with single tusk
• It's a whale of a thing to have to ward Hal like this
• Swimmer managed to get up to start when help arrived laughing
• Whale, the male of which has a spiral tusk
• Sea creature with a long spiral tusk
• Swimmer's nervous anticipation returned when help arrived laughing, initially
• Arctic whale with the male having a long twisted ivory tusk