Salmon Production in Changing Ocean Domains

Abstract

The ocean’s carrying capacity for anadromous salmonids is dynamic in time and space. It is constantly changing on interannual, decadal, centennial and millennial time scales. Since 1976 a major change has occurred in the Northeast Pacific Ocean, with unfavorable ocean conditions for salmonids in the Coastal Upwelling Domain, and highly favorable conditions farther north in the Coastal Downwelling and Central Subarctic domains and the Bering Sea. High sea levels and warm temperatures along the coast, an intense Aleutian Low, and weak upwelling are associated with these recent changes. During the 1960s and early 1970s, when hatchery releases of smolts were increased to compensate for loss of freshwater habitat, the opposite trend prevailed, with good ocean survival in the Coastal Upwelling Domain and lower survival in the Gulf of Alaska. Although the exact mechanisms that affect high or low salmon production are still speculative, ocean climate is clearly implicated and should be considered in management decisions. Favorable ocean conditions will be required for full recovery of many depressed stocks.