About once every 20 years, something that size bumps a boat in the Delaware River between Trenton and Philadelphia. Sturgeons, once plentiful there, are still reputed to be in the river but are rarely seen.
Could be a 18 great Atlantic hammerhead that are known to frequent the bay. About fifteen year ago a fishing friend of my dads was out on his 18 footer in the bay for an overnighter, and got scared out of his shoes, and dropped his Bud, when an enourmouse mouth was seen at the transom of his boat. He said eyes where easily over four feet at the ends, with one hell of a huge mouth. The shark literally lifted itself high enough to peer into his boat, with the lantern providing light. Needless to say, he decided to head home.