Up river, Oregon City to West Linn launch ramp it seems like prawn and prawn spinners.
Sellwood area seems a mix of prawn/prawn spinners and herring.
Willamette Park and down river to the mouth seems like herring.
Now why the fish's taste changes in that relatively short run of water from the mouth to Oregon City is a puzzle.
I wonder if it's not a case of the fish biting on what they see vs. what they "want". Everyone uses prawns, everyone catches on prawns. Everyone uses herring they catch on herring. Folks use a mix (Sellwood area) they get caught on a mix.
both work, just different tech for different depths. I have caught them from the columbia river and up into the willamette clear to the falls on spinners and prawns. the herring trolling works best in less current and deeper water but both will work equally as well if you stick with them.
Another interesting note in the Sellwood to upriver stretch is that as the season progresses into May, the bite will start to favor prawns over herring. I've noticed this myself and confirmed it with other anglers who fish the West Linn area. Why it happens we can only wonder.
We caught two on spinners yesterday(sunday). After fishing all day with herring and being skunked, my husband switced to a spinner he made a while back. It wasn't half an hour and he got a nice 17 1/2lber. About 15 minutes later and fish on, I caught a 19lber. Both on his spinner!! I guess the fish don't really know what they want!!