Photo: NOAA/FIS

Research Highlights Potential Refuge for Juvenile Salmon Amidst Marine Heatwaves

UNITED STATES
Monday, May 19, 2025, 05:00 (GMT + 9)

Ketchikan, Alaska – New scientific findings published by NOAA scientists suggest that the intricate network of inshore waters in northern Southeast Alaska may offer a crucial, albeit temporary, refuge for migrating juvenile salmon facing the increasingly frequent and intense marine heatwaves in the Gulf of Alaska. This research, highly relevant for the international seafood sector reliant on healthy salmon populations, sheds light on potential resilience mechanisms for these ecologically and economically vital species.

The R/V Medeia, operated by the Alaska Department of Fish and Game; one of the research vessels used to conduct the trawl survey for juvenile salmon.Photo: NOAA

The study, conducted by researchers at the Auke Bay Laboratories, Alaska Fisheries Science Center, analyzed data from periods encompassing significant marine heatwave events in the Gulf of Alaska (2014–2016 and 2019). Previous studies have established a clear link between the survival and growth rates of juvenile Pacific salmon and oceanographic conditions, particularly food availability. The recent, prolonged periods of unusually warm seawater temperatures in the Gulf of Alaska have been correlated with declines in key prey species, triggering cascading effects throughout the marine food web and subsequently leading to reduced adult salmon returns and fishery disasters.

While warming trends are strongly suspected to be a primary driver in these adult salmon declines, the new research focused on the condition of juvenile salmon before they migrated into the open Gulf. Surprisingly, the study found that the body condition of juvenile salmon in the inside waters of Southeast Alaska did not show a significant negative correlation with temperature during these heatwave years. This was highlighted by Mariela Brooks, research chemist at Auke Bay Laboratories, who stated, “We expected that this might be due to changes to their prey, potentially at the juvenile stage, because we have evidence that changes in diets are related to marine temperature. However, we found that the body condition of juvenile salmon did not show a significant relationship with temperature in the inside waters of Southeast Alaska.”

The researchers hypothesize that the unique geographical and oceanographic characteristics of Southeast Alaska played a critical role in maintaining relatively cooler water temperatures within its inshore areas, even as offshore Gulf of Alaska waters experienced significant warming. This more stable environment likely supported a diverse array of prey for the juvenile salmon, allowing them to adapt their diets and buffer against the potential negative impacts of the heatwaves. Consequently, the observed juvenile fish in these protected inshore waters did not exhibit a decline in body condition prior to their migration into the broader northeast Pacific Ocean.

<-- The R/V Medeia, operated by the Alaska Department of Fish and Game; one of the research vessels used to conduct the trawl survey for juvenile salmon.Photo: NOAA

This study underscores the ecological importance of the inshore waters of Southeast Alaska as vital early marine habitat for juvenile salmon and reinforces the value of long-term surveys that track juvenile abundance for accurate harvest forecasts. Furthermore, the findings suggest that the primary survival bottlenecks for these salmon populations during marine heatwaves likely emerge after the juveniles migrate offshore into the Gulf of Alaska.

Understanding the complete migratory pathway of juvenile salmon, including the specific times and locations where significant mortality occurs, is now deemed essential for improving the accuracy of salmon survival predictions and forecasting future returns. This knowledge will be crucial for fisheries management strategies and for mitigating the economic impacts of climate change on the international seafood sector that relies on healthy and predictable salmon stocks. The research highlights the need for continued investigation into the offshore conditions and their impact on juvenile salmon survival during these increasingly frequent warm water events.

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