Stubb was his second mate (4)

I believe the answer is:

ahab

(Other definitions for ahab that I've seen before include "Moby Dick's pursuer" , "Name of captain seeking Moby Dick" , "He hunted Moby Dick" , "sea captain" , "Captain hunting the whale Moby-Dick" .)

I've seen this clue in The New York Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.