The stripers don't swim up river till mid/late summer. I haven't been on the Delaware in a year or two, but I've heard that Eastern Snakeheads are making their way up to Bushkill and Digmens Bridge(Don't think I spelt that right).
The stripers have made their way up the river and are currently being caught around Trenton.. They come up for spawning season. Typically they make their presence known in April.
Snakeheads have been found in the area, especially on the Jersey side, but that just means that not enough people have reported them on the Philly side. I know that I've seen a lot of people catching them in the FDR park area. It's ok, they seem like they put up a good fight. I'll take it.