Shifts in fish populations show the impact of climate change on Arctic food webs and Alaska/Yukon Indigenous communities as river temperatures increase.
By Eric Hawrylyshyn
Chinook salmon (Oncorhynchus tshawytscha) and Dolly Varden (Salvelinus malma) are important species of cold-water fish to Indigenous communities in Alaska, USA, and the Yukon Territory, Canada, as they are frequently used for subsistence and commercial purposes. Chinook salmon can spend the first 1–2 years of their life in freshwater rivers before migrating to the ocean. Meanwhile, Dolly Varden can spend up to the first 4 years of their life in freshwater rivers. However, the water temperature of these river systems affects the growth and survivability of cold-water fish.
As climate change increasingly alters the waterways that Chinook salmon and Dolly Varden inhabit, it becomes critical for scientists to better understand the effects these environmental changes will have on local fish populations. The impact of climate change is highlighted by the fact that there has already been a measured decrease in Chinook salmon stock, resulting in a 7-year ban on subsistence harvests of Chinook salmon enacted in 2024.
Designing a study with climate change scenarios
Therefore, a scientific team led by researchers from University of Colorado Boulder produced a statistical model to predict the growth rate of Chinook salmon and Dolly Varden under different future climate change scenarios. The model combined several environmental factors and fish physiology data from Fish Bioenergetics 4.0, a third-party online resource that estimates fish species growth outcomes based on factors such as individual fish size, the amount of prey consumed, and species-specific estimates of physiological constants including respiration and excretion.
They used the model to predict the growth rate of Chinook salmon and Dolly Varden in seven river basins within the Arctic-Yukon-Kuskokwim (AYK) region of Alaska and the Yukon Territory, representing an area of nearly 250,000 km2. During the warmest summers, some area river temperatures can already reach >20°C (>68°F). This temperature is outside the threshold for most cold-water fish. Rivers across the AYK region are projected to warm an additional 0.95–1.58°C between 2034 and 2065. As a result of these changes in water temperature, the model predicts a negative impact of climate change on the growth rate and survival of Chinook salmon and a positive impact on the growth rate and survival of Dolly Varden.
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Bioenergetic modeling to predict fish growth
The growth rate of juvenile, also called young-of-year (YOY), Chinook salmon and Dolly Varden is dependent on water temperature. The ideal water temperature for YOY Chinook salmon was estimated to be between 7.3°C and 14.6°C (45–58°F). YOY Dolly Varden have a higher growth range of 10°C to 16°C (50–61°F). When river temperatures fall above or below these thresholds, the cold-water fish living in them undergo reduced growth and survival rates. The researchers chose YOY fish as the target of the model as the survival of individuals at this life-stage is critical for population growth and sustainability, and fish at this age are found within the river basins.
The study researchers created a model using historical climate data (1990–2021), temperature classifications expected to occur in the future (between 2034 and 2065), and data from Fish Bioenergetics 4.0. They aimed to determine how environmental changes would impact the growth rate of Chinook salmon and Dolly Varden. Beyond water temperature, the overall model also incorporated the effect of landscape and hydrology on fish physiology and growth. The researchers used this model to predict growth rates of these fish species under different scenarios of climate change.
Impact of climate change on cold-water fish growth
The researchers predicted that river basin water temperatures would increase by an average of 0.95–1.58°C in the period 2034–2065. However, they identified a clear relationship between the amount of warming and each river’s topographic and hydrographic characteristics, suggesting landscape conditions play a key role in the effect size of climate change.
While historical records showed that all seven rivers remained within the temperature threshold for YOY Chinook salmon, the projection for 2034–2065 indicated that more than half of these river basins will periodically exceed the temperature threshold for YOY Chinook salmon. However, these temperature changes will remain within the threshold of YOY Dolly Varden.
Interestingly, these climate change models also found there will be fewer summer days below the temperature threshold, which would also have a negative effect on cold-water fish growth. In select water-temperature change scenarios, such as abnormally cold years in river basins that are already among the coldest, the model surprisingly predicted that there would be an increase in growth for YOY Chinook salmon. Their growth, however, was still predicted to decrease in “average” years in warmer climate change scenarios. Meanwhile, the model predicted YOY Dolly Varden would have the largest growth rate potential under the modelled climate change scenarios.
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Connecting to Indigenous communities
The impact of climate change on the populations of cold-water fish such as Chinook salmon and Dolly Varden directly affect Indigenous communities in Alaska and the Yukon Territory. These communities have already experienced declines in Chinook salmon harvest, and as of 2024 are now banned from catching Chinook salmon in hopes of recovering the population. The loss of Chinook salmon for subsistence and commercial purposes threatens the traditional lifestyle of Indigenous communities across the AYK region. Furthermore, these cold-water fish species are important to the overall Arctic aquatic food web. The decrease in population size of these fish can also negatively impact this food web, causing additional stress to Indigenous communities in the AYK region.
It is critical to include Indigenous Knowledge at all levels of a study, especially when researching a question that impacts Indigenous communities. To incorporate Indigenous Knowledge, scientists conducting this study ran a project workshop where Indigenous community representatives identified relevant river basins and fish species to be examined. The information they provided, along with the availability of sufficient quantitative data for model simulations, resulted in the selection of the final seven river basins and species. Indigenous Knowledge was further incorporated into the creation of the model, including climate model decision-making, river usage data, and fish species mapping.
This study was published in the journal Scientific Reports.
Reference
Thomas, P. A., Blaskey, D., Cheng, Y., Carey, M. P., Swanson, H. K., Newman, A. J., Brooks, C., Herman-Mercer, N. M., & Musselman, K. N. (2025). Warming Alaskan rivers affect first-year growth in critical northern food fishes. Scientific Reports, 15(1), 28834. https://doi.org/10.1038/s41598-025-14711-8
Featured image: Fall Chinook salmon adults by Alaska Fish Habitat Partnerships Story Map Content, licensed as CC BY 2.0.
About the Author
Eric Hawrylyshyn received his Bachelor of Science in Zoology and Master of Science (MSc.) in Biomedical Science from the University of Guelph. Eric’s scientific and research interests focus on conservation, reproductive biology, and regenerative medicine. He has previously worked as a zookeeper at different zoos in Canada. In his spare time, Eric enjoys spending time in nature, reading, and exercising. Connect with Eric via LinkedIn.
