I keep records of how much hatchery fish weigh as well as length/girth. You can get a good approximation of natives with a simple length. A 36 inch steelhead of average girth goes ~ 14 pounds. 36.5, maybe 15. A girthy native will go 15 to 30% heavier than that. I'd guess your fish at about 17 pounds (a beauty). I brought home a hatchery buck with nice shoulders last winter that was 36.5 inches. It weighed 16.5 pounds.
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If every fisherman would pick up one piece of trash, we'd have cleaner rivers and more access.