why do the sharks avoid ishmael as he clings to the coffin

Melville begins the epilogue with a scriptural quote from Job, "And I am escaped alone to tell thee," once again returning to a Biblical parallel. However, the journeys of Job and Ishmael in fact contain few essential similarities other than surface details. While Job grappled with the possibility of a vengeful God, Ishmael serves as a simple narrator for the novel. He is simply a witness to the tragedy that unfolded throughout Moby Dick, and in fact is Job's opposite. In the Biblical tale of Job, his suffering was random and unjustified, while in Moby Dick it is Ishmael's good fortune that is mere coincidence, allowing him, like Job, to tell his tale.