Hi guys,
I was fishing for pike/musky yesterday in a local resevoir. It was evening and there were several groups of unidentified fish splashing, occasionally jumping, and swimming just under the surface. I could see dark long silhouettes with 5 or so silhouettes in each group.

I live in Northwest Pennsylvania and the water temperature was 51oF. The water depth was anywhere from 10-20 feet. I was fishing a bay off of the main reservoir with a creek running into it. The silhouettes were way to long to be bass or any other panfish species. I doubt they were carp as the silhouettes seemed too long/slender, however it was hard to see them from shore. They were out towards the middle of the bay, 50 or so yards from shore. They did not appear to be feeding but rather slowly swimmingly in groups.

What kind of fish were they? Could they be musky or pike spawning? Do pike or musky behave like this? I could not get them to bite however they were just out of my casting range. I did catch a 20 some inch musky in the area.

It sounds like carp spawning. They group together really tightly and make a lot of racket in the shallows and swim so closely together that it might give the impression of a much longer fish than what they actually are. 

I agree.

That's how the carp do down here when they are spawning. I often hoped it was bass chasing baitfish but I am usually not that lucky.