Different species of salmon have different peak periods which vary slight depending on where in Alaska you are planning to fish and those can vary from year to year based on climate fluctuations.
Without accounting for geographical or annual variations, here are the main periods during a summer when each of the five species of salmon are at their peak.
King Salmon (Chinook) - May through early July
Red Salmon (Sockeye) - late May to end of July
Silver Salmon (Coho) - July through August
Pink Salmon (Humpback) - July through September
Chum Salmon (Keta) - late June - late August