If it kills you to see the natives killed, don't go with him when the natives are in. There's lots of time to fish with him during the hatchery run, right? Fishing for native steelhead can be a spiritually envigorating experience. Seeing a dead native steelhead makes me feel ill. I don't have a problem with people killing them when its legal, but I don't want to take part myself. I can have just as much fun on my own, personally.

When releasing fish, I sometimes tell people I don't want to have to take the time to clean the fish later or that my freezer's full of hatchery fish already. Maybe that approach would work? I released a really hot hatchery summer steelhead last year and told my friend "Any fish that jumps 5 times for me earns its freedom."
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If every fisherman would pick up one piece of trash, we'd have cleaner rivers and more access.