As we imagine the story of this text, Captain Ahab comes along and interrupts the great whale's Sunday morning swim. And old Moby-Dick thinks, "Oh boy. Yet another crazy guy giving some insane speeches about God and the Universe from the deck of this ship. I'm so sick of being hunted."
See what we just did there? We imposed human voices and thought processes onto a non-human being. Ecocritics are interested in investigating precisely how and why we do this—how and why we're so anthropocentric.
So: how does anthropomorphizing Moby-Dick affect the reader's view of the natural world? Of human nature? Git it, good readers.