Hey Bart,
Where were you trying? Landbased by the siunds of it?
I mainly notice the stage of the tide plays a major role in where the herring are hiding. If I'm bait fishing I mainly chase bait around the floodgates in Hills Creek on the other side of the inlet, along with everyone else it seems like sometimes. This seems to be almost a guaranteed spot for bait, doesn't seem to matter which stage of the tide, the structure seems to hold them.
Time of year can have a big influence on the size though i've noticed and i guess this is related to spawning times and growth rates..