Bob is right in that the fish from the Skeena system are mostly 3 year smolts (freshwater). The length of time that steelhead smolts spend in freshwater is largely a function of the growing conditions in the freshwater environment. For steelhead to successfully make the transition from freshwater to salt water they need to reach a certain size threshold (generally 6 or 7 inches). Consequencely as one moves North from California to Alaska older smolts are found.

The growing conditions in the southern part of steelhead's range allow more fish to reach that size after only a year in freshwater, in the mid-portion of their range (Washington) two year smolts dominate (some one year and 3 year smolts) and further North 3 year smolts become the common age of smolting.

In regard to chinook those larger fish are indeed older fish (longer marine feeding). Large chinook (thus in excess of 50#) were much commoner in Washington waters 50 or more years ago. Those older fish have become much rarer in our chinook population primarily due to the continuous fishing on the immature fish on their feeding grounds. The result is our chinook populations have become on the average young at maturity thus smaller.

Tight lines
Smalma