My theory on Pyke.
I have been thinking a bit about Pyke and his lore and came to the conclusion that his memories are partially true partially fabricated. I do not believe he was betrayed by his crew nor he was a sailor on the ship called "Terror" but i do believe he was indeed a sea monster hunter. Basically my theory is that those Jaull fishes are connected to the swimming city Pyke was hunting those fishes to make a living than he got eaten by one of them. Than some kind of entity revived Pyke and altered his memories with the goal to kill all capitans because in the eyes of the swimming city all capitans are a threat, either by roaming the seas or by hunting its inhabitants like the Jaull fish. So now pyke is nothing more than an agent of the city controlled by his delusions and altered memories.
Thoughts?