Seems most likely to be a white shark, though I understand that makos will whack seals when they get really big (the bluefish only serve as a snack at that point). I've seen very large makos right off Race Point in only ~15 feet of water, close enough to surfcasters to make them fill their waders if they knew.
I'm certainly no shark expert, but I was not aware that blue sharks would take a seal, even the really big blue sharks.