I recall one study on pike minnow predation at Columbia dams. The conclusion was that while they ate lots of salmonids it could not be shown that they were eating healthy fish. The authors believed that much of th consumption was on stunned fish or fish otherwise incapacitated by passing through the dams.

IF this is true the pikeminnow in freeflowing/undammed streams aren't a problem. Further, are they eating fish that would recover and survive?