I had a similar experience with a whiting caught in dublin bay a month ago.....just the soft fleshy part around the stomach (and the stomach/guts itself) taken out, first impression was maybe a bass or the like, given that it seemed to be a bite mark too small for a seal.
But I also thought that maybe the fish had been on the hook a while (it was difficult seeing bites due to the wind), and maybe crabs had got to the fish. I was fishing quite short snoods, so the fish wouldnt have had much scope to get away from them if they were really hungry.
I guess, like all them fish that get away......it shall remain a mystery