The annual salmon run is the migration of mature Pacific salmon from the ocean upstream into Alaska’s freshwater rivers and streams to spawn. This event defines the Alaskan summer, driving one of the world’s most productive fisheries and providing a major food source for the entire ecosystem. The timing of this return varies significantly, creating a dynamic calendar that spans from late spring through the fall months. Understanding when each species returns is key to appreciating the scale and complexity of this natural phenomenon.
Seasonal Timing by Salmon Species
The five main species of Pacific salmon found in Alaska each adhere to a distinct seasonal schedule, ensuring that the streams are continuously populated by returning fish from May into October. The King salmon, or Chinook, are the earliest to arrive, beginning their migration into freshwater systems as early as mid-May. This run generally continues through the end of July, often featuring two separate pulses of fish in many river systems.
Sockeye salmon, also known as Reds, dominate the mid-summer period, peaking between late June and early August. This species is the most numerically significant run in the state. Chum salmon, or Dogs, overlap heavily with the Sockeye, with their main runs occurring from late June through September.
The Pink salmon, or Humpies, are the most abundant species overall but exhibit a distinct two-year cycle in many regions, meaning large runs occur only in even-numbered years. Their migration is concentrated over a shorter window, usually peaking between July and early September. Coho salmon, or Silvers, are the latest to arrive, offering a strong run that often begins in August and extends well into October, marking the close of the primary salmon season.
Regional Variations in Alaska’s Salmon Runs
Alaska’s immense size means that the run timing for a single species can shift by weeks depending on the geographic region. In Southeast Alaska, which benefits from warmer coastal waters, the King salmon run often begins in mid-May, with the bulk of the local fish passing through the river systems by the first week of July. This early timing reflects the southern latitude of the Panhandle compared to other parts of the state.
Moving north to the Southcentral region, specifically the Kenai River, the King salmon run is managed as two distinct groups: an early run from mid-May to the end of June and a later, often larger run that begins on July 1st. The peak of this later run occurs between the second and third weeks of July, two to three weeks after the main surge in the Southeast. The Sockeye salmon run also shows this stagger; while the Kenai River’s main Sockeye run peaks in mid-July, the Bristol Bay run, located further west, begins in early June, with the peak concentrated in July.
These differences are driven by the time it takes for the fish to travel to their natal streams and the local water temperatures that trigger their final push inland. Western Alaska, including Bristol Bay, hosts the world’s largest Sockeye return, which starts its migration slightly earlier than the Kenai River’s main run. The scale of the return in Bristol Bay—often tens of millions of fish—defines the mid-summer season in that region.
Environmental Factors Affecting Run Predictability
While historical data provides a reliable calendar for the runs, the exact start and peak dates can shift annually due to natural variables. Water temperature is one of the most significant factors, acting as a cue for migration and a stressor once the salmon enter freshwater. If river temperatures rise above 64 degrees Fahrenheit for an extended period during the spawning season, it can cause a decrease in Chinook productivity and even lead to mass die-offs, as occurred in a record hot year.
Low river flow and drought conditions can also delay the migration, forcing salmon to hold in cooler marine waters rather than risk the costly swim upstream. Conversely, a surge of high water from heavy rainfall can accelerate the movement of fish, allowing them to bypass difficult sections of the river more easily. The timing of these freshwater conditions is important for species like Coho and Pink salmon, which return later in the season.
Ocean conditions during the years the salmon spend at sea are another variable that affects the run, influencing the overall size of the returning population. Events like the El Niño Southern Oscillation can affect the marine food web, which impacts the health and number of adult salmon that survive to make the spawning migration. A combination of ocean productivity and freshwater variables dictates the precise timing and strength of the run in any given year.