All Chinook have black gum lines and tongues throughout there life cycle. Below is cut and pasted from:
http://www.leeroysramblings.com/PS_Blackmouth_history.htm
Puget Sound Fish :
Some of the Puget Sound fish, may have been smarter, or lazy & found enough food in the sound, so they never left for northern waters. In the early 1960s the Dept of Fisheries set out to duplicate by hatchery methods, a fish that would stay as a resident in the sound. If this could be duplicated, we as sport fisherpersons could have a year around salmon fishery in the sound.
Frank Haw was selected for this job. His extensive testing revealed that by releasing the fish from a hatchery facility one year after the normal time, (15 months of age), that a majority of these fish lost their instinct to migrate great distances, if the food chain is available to them. At this time these fish were being raised in Percival Cove, a fresh water impoundment in of Capitol Lake in Olympia.