Very interesting...
Just so you know, I once caught a bluefish (small) in the Manasquan a couple hundred yards downstream from the bridge at Bryce Park. If the salt line was far enough up the river, that may offer an explanation as to what those fish were. I'd be particularly interested in knowing how the angler missed the fish; if they bit through the line, then bluefish are probably the culprit.
If they weren't bluefish... well, then we all know what they most likely were.

__________________
Now the sun is just starting to climb up over the treetops,
And it's gonna be a beautiful day, that's plain to see.
But I won't be around at all, so don't even bother to call,
Cause on a day like today there's one place I gotta be:
GONE FISHIN'
Fishing with LardAlmighty on YouTube