I'm not aware of a context where immortal refers to organisms that can't be killed by accidents and predators. In mythology and novels alike, vampires, gods, elves, ..., are all called immortal and still can be killed.
I thought crocodiles or alligators (forget which one) were immortal and they tend to die only because they get so big and can't eat enough to maintain life eventually. But, they're not on this list?
