These mechanisms of PDO provide a large forage base for the salmon. This has been explained by the effects that PDO has on regional weather patterns. The warm moist air that is present in Alaska is a result of the warm near coastal waters, which act as a feeding mechanism for the cyclonic pattern, much like the Gulf of Mexico provides moisture for the central United States. The increased winter precipitation results in large snow packs that are released during the spring thaw. The Alaska populations tend to be much more compatible with PDO index, which could be due to a variety of factors.
Alaskan salmon are mostly wild stocks that are less influenced by human induced factors.
The salmon in the Pacific Northwest are mostly hatchery fish that face impediments such as dams and pollution in their environment. The PDO seem s to be the primary driving force in Alaskan salmon populations, while the Pacific Northwest salmon seem to have a variety of influences. With the signature sea surface temperature shifts, bring increased populations of bottom levels of the food chain. Oceans currents bringing nutrients and zooplankton to the near coastal region enhance this. Stream flow rates are also partially responsible for nutrient loading in the near coastal waters, which are now rich in biological productivity.