How the Warming Bering Sea is Reshaping Alaska’s Salmon Story
Summary:
No single factor explains the decline, but the thread tying them together is a rapidly warming environment.
Warmer oceans are reshaping food webs, leaving young salmon with less nutritious prey and higher energy demands during their most vulnerable first year at sea.
These ecological pressures ripple outward—affecting different salmon species in uneven ways and disrupting the communities, cultures, and economies that depend on them.
Once salmon leave Alaska’s rivers, they enter a marine world that’s shifting faster than ever before.
Recent years have brought record-breaking heatwaves in the Bering and Gulf of Alaska, thinning sea ice, and profound changes in the food web. These transformations are reshaping where and how salmon find food, how fast they grow, and even which species thrive.
For western Alaska’s Chinook and chum salmon, the changes have been especially difficult. Scientists tracking juvenile fish over the last two decades have found that in warm years, like 2016 and 2019, young salmon enter the ocean to find prey that’s smaller and less nutritious. Their metabolisms speed up in the heat, demanding more food just as energy-rich zooplankton and high-fat forage species like capelin and sand lance—species critical for young salmon growth—decline. Instead, juvenile chum are eating more jellyfish, which provide barely half the calories of their normal prey.
The result: thinner, less resilient fish with fewer energy reserves to survive their first winter.
A “Double Whammy” at Sea
That first year for a young salmon is critical, and warming waters have added a new layer of risk. Juvenile chum salmon now face what NOAA scientists call a “double whammy.” They first encounter unusually warm conditions and poor prey in the northern Bering Sea, then meet similar conditions when they migrate to the Gulf of Alaska to overwinter. At both stages, higher temperatures increase their energy needs while reducing food quality. Many simply don’t make it back.
Even species that seem to benefit at first are feeling the strain. During the recent marine heatwave period (2014–2019), scientists actually counted more juvenile chum salmon in surveys than in cooler years—but those higher numbers never translated into more adult fish returning home. In other words, warm water helped more juveniles reach the ocean, but fewer survived long enough to spawn. It’s a stark reminder that abundance at one life stage doesn’t guarantee recovery later.
Different Species, Same Pressure
Western Alaska’s salmon species are responding differently to the same environmental pressures. Chinook salmon, once abundant along the Yukon and Kuskokwim Rivers, have declined for decades, with the 2022 run coming in 81% below the 30-year average. Chum salmon followed suit more recently, plummeting 92% below average in 2021. Meanwhile, sockeye salmon in Bristol Bay surged to record highs during the same period—proof that climate change doesn’t move all species in the same direction.
Scientists studying Chinook have pinpointed several stress points: warmer freshwater temperatures that reduce survival of juveniles, altered migration timing tied to rainier summers and earlier ice breakup, and increased disease rates, including a parasite called Ichthyophonus. New research also shows that as ocean conditions shift, juvenile salmon may become more exposed to predators. Changes in temperature, turbidity, and prey fields can influence when and where salmon are vulnerable, adding another layer of mortality pressure.
Combined with changing food webs in the ocean, these pressures create a complex picture. No single factor explains the decline, but the thread tying them together is a rapidly warming environment.
What Science Is Doing Next
NOAA and partner agencies are now focusing on how shifting ocean conditions, particularly in the first marine year, affect salmon survival. Long-term monitoring programs in the Bering and Gulf of Alaska track prey availability, salmon diet, growth, and body condition. Genetic research helps identify where salmon caught at sea originate, while new ecosystem models are connecting the dots between sea ice loss, plankton shifts, and predator competition.
Researchers are also integrating Indigenous knowledge and community observations, combining traditional insights with data to understand what’s happening across Alaska’s vast and varied coasts. Together, these efforts aim to forecast salmon returns more accurately and guide adaptive management as the climate continues to change.
Looking Ahead
The science is clear: Alaska’s salmon face their toughest test in the ocean that’s warming around them. Protecting these fish means looking beyond the shoreline—to the broader marine ecosystem that sustains them. By grounding decisions in solid science and long-term monitoring, we can better understand what’s driving change, and chart a smarter course for the salmon, and the people, who depend on them.
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References
NOAA Fisheries (2022). What’s Behind Chinook and Chum Salmon Declines in Alaska?August 23, 2022. Alaska Fisheries Science Center and Alaska Department of Fish and Game collaborative research summary.https://www.fisheries.noaa.gov/feature-story/whats-behind-chinook-and-chum-salmon-declines-alaska
NOAA Arctic Report Card (2023). Divergent Responses of Western Alaska Salmon to a Changing Climate.January 23, 2024. Joint contribution by NOAA Fisheries, Alaska Department of Fish and Game, and partner institutions.https://arctic.noaa.gov/report-card/report-card-2023/divergent-responses-of-western-alaska-salmon-to-a-changing-climate/
NOAA Fisheries (2024). New Evidence of Marine Heatwave Impacts on Western Alaska Chum Salmon.Alaska Fisheries Science Center feature, summarizing recent study by NOAA and ADF&G scientists.https://www.fisheries.noaa.gov/feature-story/new-evidence-marine-heatwave-impacts-western-alaska-chum-salmon
Suryan, R. M. et al. (2021). Heatwave-induced synchrony within forage fish portfolio disrupts trophic stability at the onset of the 2014–2016 Pacific marine heatwave. Communications Biology, 4(1), 1–12.https://pmc.ncbi.nlm.nih.gov/articles/PMC8048560/
Wells, B. K., et al. (2025). When, where, and why salmon become vulnerable to predation. ICES Journal of Marine Science, 82(9), fsaf162.https://academic.oup.com/icesjms/article/82/9/fsaf162/8257207
