The theme that is supported by the passage is:
Fear makes people behave in strange ways.
In the conversation between Rainsford and Whitney, Whitney describes a sense of dread and unease that he feels as they approach the island, suggesting that fear can impact perceptions and behaviors, even among seasoned sailors. Rainsford dismisses these feelings, but the implication is that fear can influence how people react to their surroundings, aligning with this theme.