chinook Salmon juvenile or adult

How do I tell the difference between an adult Chinook and a juvenile chinook.
Are we talking about a water with landlocked Fall Chinook or a river system that Chinook Salmon can use to reach the ocean? Anadromous (ocean-going) juvenile Chinook are typically defined as being two years of age or less.  They will be 3 - 5" in length - depending on their diet and water temperatures.  At approixmately 18 months of age they begin to smolt (body change to adapt to salt water).  They become silvery and usually begin their downstream migration to the ocean.  When they return to fresh water (1 - 3 years later) they are considered adults.  Chinook Salmon that live one year in the ocean are mostly males and will be 20 - 24" in length.  Two and three-ocean fish will be considerably larger.   Land-locked Chinook Salmon are stocked in several locations around Idaho to help manage Kokanee Salmon populations.  They are raised in a fish hatchery for their first year of life and will grow to 8 - 10".  When stocked in reservoirs they typically begin eating juvenile Kokanee and add roughly 8 - 10" of length per year.  Land-locked Fall Chinook will live 4 - 5 years in most Idaho reservoirs.  Most are unsuccessful at naturally reproducing.
Answered on: 
Monday, June 1, 2015 - 8:15 AM MDT