What was mafatu's job in the book call it courage?

In the part where Mafatu killed the hamerhead, Mafatu could not kill the hamerhead because it was eating the fish bate and ruining his trap. But when Uri fell in the sea and the hamerhead charged Mafatu had the courage to kill the shark. You could call that courage or you could not, but I call it the very best type of courage.