It was a terrific, most pitiable, and maddening sight. The whale was now going head out, and sending his spout before him in a continual tormented jet; while his one poor fin beat his side in an agony of fright. Now to this hand, now to that, he yawed in his faltering flight, and still at every billow that he broke, he spasmodically sank in the sea, or sideways rolled towards the sky his one beating fin. So have I seen a bird with clipped wing making affrighted broken circles in the air, vainly striving to escape the piratical hawks. But the bird has a voice, and with plaintive cries will make known her fear; but the fear of this vast dumb brute of the sea, was chained up and enchanted in him; he had no voice, save that choking respiration through his spiracle, and this made the sight of him unspeakably pitiable; while still, in his amazing bulk, portcullis jaw, and omnipotent tail, there was enough to appal the stoutest man who so pitied.
—The Pequod Meets The Virgin
The killing of an old, injured, blind Sperm Whale is a scene both to relish and abhor, depending on your feeling, and can be found in Chapter 81: The Pequod Meets The Virgin.
While little King-post, Flask, enjoys the killing of this poor old man of the sea, Starbuck, the pious first mate, finds something wrong in the vigorousness and pleasure derived from murdering the whale. Despite these feelings, however, the whale must be taken, for there is much oil in this old bull, and less fight in him than in his younger relatives.
When at last, the Old Bull is killed, the carcass, too lean and unhealthy to float, sinks, and deprives the Pequod of his oil. Rolling against the carcass of the Old Bull sinking is certainly optional, but is not present in the core rules, since killing him in the first place is hard enough.