A large number of runs are also found in the Canadian portion of the Yukon River. May. There may also be a summer run in June and July and another in August and September. Some river systems have more than one stock of chinook, sometimes with the stocks migrating in spring, summer and fall. Fish in the early runs usually go farthest upstream, with those in later migrations spawning closer to salt water. While the majority of chinook salmon head for sea a few months after they emerge from the gravel, some remain in their home stream for one or two years.
Chinook returning to spawn vary greatly in age - from two to eight years.
In the Yukon River, a northern stream, almost all chinook spend their first year in fresh water. In the sea, chinook feed on large zooplankton, herring, sand lance and many other fish, ranging widely in the ocean and growing rapidly during their last year in salt water. Those spawning after three or four summers of feeding at sea weight from 6.75 to 25 kg.