Dorsal fin height is not an effective tool to distinguish hatchery and wild steelhead in the field.

This article evaluates the effectiveness of using dorsal fin height as a harvest control rule to distinguish hatchery-origin and wild steelhead (Oncorhynchus mykiss) in coastal Washington populations. The study found that while hatchery steelhead generally have shorter dorsal fins than wild fish, dorsal fin height strongly correlates with fish length and age, causing significant overlap between hatchery and wild fish and resulting in frequent misidentification. A static dorsal fin height threshold correctly identified 90% of hatchery fish but misclassified 44% of wild fish as hatchery, posing conservation risks. In contrast, adipose fin clipping—a method involving removal of the adipose fin in hatchery fish—accurately identified 97% of wild fish and is recommended as a more reliable, low-cost tool for fisheries management. The authors conclude that dorsal fin height is an ineffective regulatory measure and advise discontinuing its use in favor of adipose fin clipping to better balance harvest objectives with wild steelhead conservation.