Idunno, I feel like they certainly fathom it to some degree. They have an awful lot of funky little predator evasion techniques for an animal with no fathom.

That whole schooling thing is a bunch of fish going, I know they like eating us, but I'd rather they eat YOU.

I do agree that they have no conception of humanity, just that sometimes their friends get raptured away by something that makes a boat noise.