Virtually all of the rivers that have odd-year runs of humpies also have smaller even-year runs. I've fished the Stilly since somewhere around 1954 and there have ALWAYS BEEN odd-year humpies in the river. The runs are only a small fraction of the size of the even-year runs, but they have probably been there since the end of the last ice age. Pilchuck Creek in particular seems to get unusually large numbers of them.