The Idaho Department of Fish and Game reminds steelhead anglers that fall-run chinook salmon will be found in area rivers this fall. Some of these fish will have missing adipose fins, similar to hatchery steelhead, but all fall chinook must be released immediately. Snake River fall chinook salmon are federally listed as "Threatened" and are protected throughout their range in Idaho waters.
The easiest way to distinguish a chinook salmon from a steelhead is by checking the lower gum line of the jaw. If the lower gum is black, it's a chinook. Using the gum line test, identification can be made quickly without taking the fish out of the water.
Another feature that helps differentiate chinook salmon from steelhead is the spotting on the back and tail. The dark spots on the back of a chinook are blotchy and irregular in shape. On a steelhead, the spots are rounded and more uniform. The black spots on the upper part of the tail fin of a chinook are large in comparison to the spots on the tail of a steelhead. Fall Chinook may range in size from 5 to 40 pounds.
By November, most fall chinook salmon are so dark in color that the spots have become obscured. Fall chinook spawn in November in the lower mainstem Snake, Clearwater, and Salmon rivers. Most will spawn and die by the end of the year.