I have fished regularly in BC for coastal salmon and can confirm that using a “cut-plug” (fresh herring trolled without the head), or a herring plastic cap/herring strip is one of the most effective rigs to use when you are trolling for coastal salmon.
Well Great Lakes salmon trollers can now fish the Luhr Jensen Cut Bait Head/Strip which is just as effective when spoons or flasher and flies just don’t produce fish. The heads/bait comes in different colors to meet the changing water and light conditions. If you have not tried them yet, they really work, especially when all else fails!!