...the whale was able to disguise itself as an island. According to some traditions, the whale’s back was covered with rocks, dirt, and even trees and bushes in the creation of this grand facade. Such a tempting oasis within the sea readily attracted sailors and wayward monks, who settled upon this island and made camp. However, this paradise of the weary sailors was interrupted when they started their cooking fire, for their island haven would suddenly dive to the bottom of the sea and drown the men, or the whale would swim off into the remotest corners of the ocean. In effect, their sins had driven them to hell, here on the back of the great monstrous fish.
– – “Bad to the bone”? The Unnatural History of Monstrous Medieval Whales
The whale became a negative oceanic figure in Christianity – it’s your fault, sailor, that you were lured into this deception. This traces back to Physiologus, and seems to be an adaptation of a land-based monster’s tale of of deception from India (recounted in a supposed letter from Alexander to Aristotle).
TH White translated a 12th century bestiary this way:
Now this is just the way in which unbelievers get paid out, I mean the people who are ignorant of the wiles of the Devil and place their hopes in him and in his works. They anchor themselves to him, and down they go into the fires of Hell.
– T. H. White, trans. The Bestiary: A Book of Beasts; Being a Translation from a Latin Bestiary of the Twelfth Century, 1954 (excerpt)
TH White had his own issues with transgression and temptation (read H is for Hawk and cry for the man).
Poor whale.