Many steelheaders use single egg imitation salmon & trout eggs in the fall (since there are salmon and migratory brown trout spawing), but they don’t use them in late winter when tributaries open up thinking there are no single eggs that can drift downstream. Well, there can still be decomposing salmon carcases in differente stages and with some salmon that did not finish spawning, or died just before spawning, their eggs can still be released as their body decomposes further. This is especially the case since we have had such a cold winter/cold water that would have preserved or slowed down the decay process.
Recently, 90% of the migratory brown trout and steelhead that I have been catching have been in-deed on single egg imitations. This is where the TriggerX line of single eggs in the various colors can out-produce fresh spawn.