We’re going to go ahead and say that this chapter is from Ishmael’s perspective.
Really, though, it’s just first-person narration, and the "I" that’s speaking here could just as easily be the faceless narrator and/or Melville himself. (A lot of the whaling experience that’s referenced here is from Melville’s own life.)
The narrator claims that he has to give some more background on whaling in order to prove a few things. He mentions them in no particular order.
First, he says, he knows of three separate occasions when a (a) whale had an initial encounter with one man, (b) escaped with the man’s harpoon stuck in him, (c) met the same man again later, but (d) lost the fight that time and got slaughtered.
There’s no possibility of mistake, he says, because the previous harpoons, which had personal markings on them, were still in the whales.
Second, there have been several times when specific whales became well known and identifiable by their markings and personalities.
Such whales have been given names by sailors—Timor Jack, New Zealand Tom, Morquan, Don Miguel.
Each of these famous whales was eventually hunted down by a whaling captain who got a bit obsessed with him. So there’s some real-life precedent for this whole Ahab-versus-Moby-Dick thing. History is repeating itself.
The narrator also mentions a few different whaling catastrophes, just to make it clear that Moby Dick is a real sea adventure story, not "a monstrous fable" or "a hideous and intolerable allegory" (45.7).
So, this white whale is super-symbolic of everything (see, oh, all of Chapters 41 and 42), but it’s also not just a symbol.
First, the narrator says, whaling and fishing are generally known to be dangerous, but people don’t usually realize just how dangerous they are (clearly, this novel predates the Discovery Channel’s Deadliest Catch). Most deaths at sea don’t get reported in your local New England newspapers.
Second, even though regular idiot landlubbers like us know whales are big, they don’t usually seem to realize just how powerful and dangerous they are.
Sperm whales, the narrator claims, sometimes deliberately attack and sink ships. He gives several examples of this happening:
In 1820, the Essex was attacked by a whale that bashed its head against the ship in order to sink it. (This is the story that’s explored in the documentary Moby Dick: The True Story, by the way.)
In 1807, the Union sank under what might have been similar circumstances, although nobody really knows any details.
About twenty years before, an American warship was sailing the Pacific, and during a conversation about whaling, the Commodore laughed off the idea that a whale could damage his ship at all.
The irony gods seemed to hear this: a few weeks later, a sperm whale damaged the hull so badly that the ship had to head straight for port, pumping water out of the hold the whole time.
On another occasion, at the beginning of the nineteenth century, a Russian ship struck a surfaced whale almost the way it would hit an iceberg, and the whole ship was lifted three feet out of the water, but ended up unscathed.
Something similar happened to a ship sailing toward Juan Fernandes (a group of Pacific Islands)— the ship seemed to hit something very hard, but there wasn’t any rock there, and they eventually decided it had been an earthquake. The narrator, however, thinks that a whale hit the bottom of the ship’s hull.
The narrator claims that he has many examples "of the great power and malice of the sperm whale" (45.19), but decides to give just one more: a legend that, in the sixth century, a magistrate of Constantinople named Procopius recorded the capture of a sea monster that had been destroying ships in the area for fifty years.
The narrator claims, based on circumstantial evidence, that this must have been a sperm whale. (Not exactly a rock solid case.)