Symbolism, Imagery, Allegory
Sharks rarely represent anything good. If this story is anything like Moby Dick, or The Old Man and the Sea, a shark might represent something like death or encroaching death. This story is a little different, though.
By the time the shark shows up, we're well aware of how scared of death the men are, but they're pretty worn out at this point—the shark is not the only danger they face. If we focus on the correspondent's reaction to seeing the shark, we notice that he's not necessarily afraid, he just wishes someone else were awake with him to see it. It's almost like he's not so scared of dying so much as dying alone. The arrival of the shark marks a change in the way the correspondent sees the world, placing more importance on appreciating the moments of life he has left than fearing death itself.