Steelhead and salmon distinct population segments

The National Oceanic and Atmospheric Administration, in cooperation with the U.S. Fish and Wildlife Service and Environmental Protection Agency, groups steelhead and salmon into distinct population segments (DPS). There are currently 15 DPS for steelhead (Oncorhynchus mykiss) and 31 evolutionarily significant units (ESU) for five species of Pacific salmon Oncorhynchus.

Source: Wikipedia — Steelhead and salmon distinct population segments (CC BY-SA 4.0)