Report on the Projected Impacts of River Warming on Fish Populations in the Arctic-Yukon-Kuskokwim Region

Executive Summary

A comprehensive assessment was conducted to evaluate the impacts of climate change on the hydrology and temperature of Arctic and subarctic rivers and the subsequent consequences for key migratory fish species. This report focuses on the young-of-year (YOY) growth potential of Chinook salmon (Oncorhynchus tshawytscha) and Dolly Varden (Salvelinus malma) in seven river basins within the Arctic-Yukon-Kuskokwim (AYK) region. The study, guided by Indigenous communities, utilized a model chain integrating climate, hydrologic, and fish-growth simulations for a historical period (1990–2021) and a future mid-century projection (2034–2065). Results indicate that while historical summer water temperatures remained within safe thermal limits, mid-century warming will create divergent outcomes. Chinook salmon growth is projected to be limited, with declines in the warmest years. Conversely, Dolly Varden are expected to benefit significantly, with growth projections nearly doubling, suggesting an expansion of suitable habitat. These findings have critical implications for several Sustainable Development Goals (SDGs), particularly SDG 13 (Climate Action), SDG 14 (Life Below Water), and those related to the food security and livelihoods of Indigenous communities (SDG 1 & 2). The species-specific results can guide research and management actions to identify thermal refugia and support community adaptation strategies.

Climate Change, River Ecosystems, and Sustainable Development

The Challenge of Arctic Warming

The Arctic and subarctic are warming at a rate nearly four times the global average, a critical issue that directly relates to SDG 13 (Climate Action). This rapid warming profoundly alters regional watersheds, affecting precipitation, permafrost stability, and glacial dynamics, which in turn impact river temperatures and streamflow. These environmental changes pose a direct threat to freshwater ecosystems and the species within them, challenging the objectives of SDG 14 (Life Below Water) and SDG 15 (Life on Land).

Impacts on Fisheries and Indigenous Communities

Migratory fishes are central to the ecological balance of Arctic aquatic food webs and are of immense cultural and subsistence importance to Alaska Native and First Nations Indigenous communities. The health of these fish populations is intrinsically linked to community well-being, food security, and cultural continuity, making this a key issue for SDG 1 (No Poverty) and SDG 2 (Zero Hunger). The decline of keystone species like Chinook salmon, which has already led to harvest moratoriums, exacerbates inequalities and threatens traditional livelihoods, highlighting the need to address SDG 10 (Reduced Inequalities). This study was developed through a co-production framework with Indigenous community representatives, embodying the principles of SDG 17 (Partnerships for the Goals) to ensure the research is relevant and actionable for those most affected.

Projected Changes and Species-Specific Consequences

River Temperature Projections

Simulations project a significant warming trend across the seven studied river basins by mid-century.

• Average summer river temperatures are projected to warm by 1.26°C.
• Historically, no river basins exceeded deleterious temperature thresholds for the studied species.
• By mid-century, four of the seven rivers are projected to exceed the upper growth threshold for YOY Chinook salmon (14.6°C) for an average of 9.4% of the summer during the warmest years.
• In contrast, all rivers are projected to remain below the upper growth threshold for YOY Dolly Varden (16°C), even in the warmest mid-century years.

Differential Growth Outcomes

The projected warming will not affect all species equally, leading to distinct future scenarios for habitat suitability.

1. Chinook Salmon (Loser): While warming may offer marginal growth benefits in colder years by reducing the number of days below the optimal thermal range, this is offset by significant negative impacts. In the warmest years and warmest river basins, increased metabolic demands at temperatures above their thermal optimum (identified in simulations around 11.7°C) will likely lead to reduced growth and smaller end-of-summer size.
2. Dolly Varden (Winner): With a higher thermal growth range (10–16°C), YOY Dolly Varden are poised to benefit substantially from warming waters. Historically, growth was limited by cold temperatures. Future simulations show a near-doubling of individual growth potential across all river basins, suggesting a significant increase in thermally suitable habitat for this species.

Implications for Sustainable Development Goals (SDGs)

SDG 13: Climate Action & SDG 14: Life Below Water

This research provides tangible evidence of climate change impacts on freshwater ecosystems, fulfilling a key target of SDG 13. The findings underscore the vulnerability of cold-water specialist species like Chinook salmon and signal a fundamental restructuring of aquatic ecosystems. Identifying potential thermal refugia—colder rivers resilient to warming—is a critical climate adaptation strategy to protect biodiversity and maintain ecosystem function, directly supporting the conservation goals of SDG 14.

SDG 1: No Poverty & SDG 2: Zero Hunger

The projected decline in Chinook salmon growth potential directly threatens the food security and subsistence economies of Indigenous communities, undermining progress toward SDG 1 and SDG 2. The collapse of this critical food source has already created a crisis in the Yukon River basin. The potential for Dolly Varden to thrive in warmer waters may present an opportunity to diversify subsistence harvests, but this requires careful management and further research to ensure population sustainability and cultural acceptance as an alternative resource.

SDG 10: Reduced Inequalities & SDG 17: Partnerships for the Goals

The impacts of climate change on culturally significant species disproportionately affect Indigenous peoples, deepening existing inequalities, a core concern of SDG 10. This study’s reliance on a co-production model, where Indigenous representatives guided the research focus on specific species and river basins, exemplifies the collaborative approach advocated by SDG 17. Such partnerships are essential for generating equitable and effective climate adaptation strategies that respect and integrate Indigenous Knowledge.

Conclusion and Recommendations for Future Action

The warming of Alaskan rivers is projected to create species-specific shifts in growth potential, favoring the generalist Dolly Varden over the cold-water specialist Chinook salmon. This ecological transformation has profound implications for regional biodiversity and the human communities that depend on these fisheries. To address these challenges and work towards a sustainable future, the following actions are recommended:

1. Prioritize Conservation of Thermal Refugia: Identify and protect river basins and headwater streams that are projected to remain cool, such as the Aniak, Andreafsky, and Teedriinjik Rivers. These areas will be critical for the survival of YOY Chinook salmon and other cold-water species.
2. Enhance Monitoring of “Winner” Species: Increase research and monitoring of Dolly Varden populations to understand their distribution, status, and resilience. This knowledge is vital to assess their potential as a sustainable subsistence resource in a changing climate.
3. Strengthen Collaborative Research and Management: Continue to use and fund co-production frameworks that integrate scientific modeling with Indigenous Knowledge. This approach ensures that research is relevant and that management strategies are developed in partnership with the communities they are meant to serve, aligning with SDG 17.
4. Support Integrated Policy Action: Advocate for policies that simultaneously address the global drivers of climate change (SDG 13) and provide resources for local adaptation measures. This includes supporting Indigenous-led conservation efforts and developing community-based adaptation plans to safeguard food security and cultural heritage (SDG 1, 2, 10).

Analysis of Sustainable Development Goals in the Article

1. Which SDGs are addressed or connected to the issues highlighted in the article?

The article addresses several interconnected Sustainable Development Goals (SDGs) by examining the impacts of climate change on Arctic river ecosystems, the fish species within them, and the Indigenous communities that rely on these resources.

1. SDG 13: Climate Action
   • The entire study is framed around the impacts of climate change. It explicitly states, “Arctic and subarctic rivers are warming rapidly, with unknown consequences for migratory fishes,” and uses climate simulations to project future conditions. This directly relates to understanding and responding to climate impacts.
2. SDG 14: Life Below Water
   • The article focuses on the health and survival of migratory fish species (Chinook salmon and Dolly Varden). Although these are freshwater habitats, the anadromous life cycle of these fish connects them to marine ecosystems. The study’s goal of identifying “thermal refugia” and understanding population dynamics is central to conserving aquatic life. It also mentions the collapse of Chinook salmon stocks and moratoriums on fishing, which are key concerns of SDG 14.
3. SDG 15: Life on Land
   • This goal includes the protection of inland freshwater ecosystems. The article’s core subject is the changing hydrology and temperature of “Arctic and subarctic watersheds” and “river ecosystems.” It analyzes how these changes affect biodiversity (species-specific impacts on fish) and the overall health of these ecosystems.
4. SDG 2: Zero Hunger
   • The article explicitly links the health of fish populations to the “food security of Alaska Native and First Nations Indigenous communities.” It highlights that these fish are critical for “subsistence” and notes the decline in household use of Chinook salmon due to stock collapses, directly addressing access to sufficient and nutritious food.
5. SDG 1: No Poverty
   • The article discusses the impact on “subsistence livelihoods” of Indigenous communities. The collapse of a primary subsistence resource like salmon can create economic and social shocks for these communities, increasing their vulnerability, which is a key concern of SDG 1.
6. SDG 6: Clean Water and Sanitation
   • While not about sanitation, this goal’s target to protect and restore water-related ecosystems is highly relevant. The study analyzes the degradation of water quality (thermal pollution) in river basins due to climate change, stating that “environmental changes in watersheds that affect streamflow and river temperature have the potential to impact fish physiology.”
7. SDG 17: Partnerships for the Goals
   • The research methodology highlights a partnership between scientists and local communities. The article notes that the study was conducted with “input and guidance from Indigenous communities” and that “Indigenous community representatives identified relevant river basins and fish species through a participatory mapping exercise.” This co-production of knowledge is a core principle of SDG 17.

2. What specific targets under those SDGs can be identified based on the article’s content?

Based on the article’s content, several specific SDG targets can be identified:

1. Under SDG 13 (Climate Action):
   • Target 13.1: Strengthen resilience and adaptive capacity to climate-related hazards and natural disasters in all countries. The article directly supports this by providing data that “can guide future research on refugia for these species” and inform “community subsistence adaptation plans and conservation measures.”
2. Under SDG 14 (Life Below Water):
   • Target 14.2: By 2020, sustainably manage and protect marine and coastal ecosystems to avoid significant adverse impacts, including by strengthening their resilience, and take action for their restoration… The study’s focus on identifying “thermal refugia” and understanding how warming limits fish growth is fundamental to protecting and managing these connected aquatic ecosystems.
   • Target 14.4: By 2020, effectively regulate harvesting and end overfishing… and implement science-based management plans… to restore fish stocks… The article mentions the “seven-year moratorium on subsistence harvests of Chinook salmon” and the “collapse” of stocks, highlighting the need for and existence of management plans based on scientific understanding, which this study aims to improve.
   • Target 14.a: Increase scientific knowledge, develop research capacity and transfer marine technology… The study is a direct example of this, using “climate, hydrologic, and fish-growth simulations” to generate new knowledge about climate impacts on fish.
3. Under SDG 15 (Life on Land):
   • Target 15.1: By 2020, ensure the conservation, restoration and sustainable use of terrestrial and inland freshwater ecosystems and their services… The entire paper is an assessment of the health of inland freshwater ecosystems (Arctic rivers) and the sustainability of their key service (providing fish for subsistence).
   • Target 15.5: Take urgent and significant action to reduce the degradation of natural habitats, halt the loss of biodiversity and… protect and prevent the extinction of threatened species. The research addresses the degradation of fish habitat (warming waters) and its species-specific consequences, noting that “Chinook salmon growth was limited, with declines in the warmest years.”
4. Under SDG 2 (Zero Hunger):
   • Target 2.1: By 2030, end hunger and ensure access by all people, in particular… people in vulnerable situations… to safe, nutritious and sufficient food all year round. The article directly addresses the vulnerability of Indigenous communities whose food security is threatened by the decline in salmon, a critical food source.

3. Are there any indicators mentioned or implied in the article that can be used to measure progress towards the identified targets?

Yes, the article mentions and uses several quantitative and qualitative indicators that can measure progress towards the identified targets.

1. Indicators for Ecosystem Health and Climate Impact (SDG 13, 14, 15):
   • River Water Temperature: The article provides specific temperature data, such as the historical average range (8.77 °C to 11.68 °C) and the projected warming (“by 1.26 °C”). This is a direct indicator of climate impact on freshwater ecosystems.
   • Days Exceeding Thermal Thresholds: The study measures “the frequency of days and river length in the upper-temperature range for individual growth.” For example, it projects that some rivers will exceed the 14.6 °C threshold for Chinook salmon for an “average of 8.75 days” per summer by mid-century. This is a precise indicator of habitat degradation.
   • Fish Growth Potential and Body Size: The bioenergetics model produces “end-of-season weight” as a key output. The finding that Chinook salmon growth declines while Dolly Varden growth doubles serves as a species-specific indicator of climate resilience and habitat suitability.
2. Indicators for Fish Stock Status (SDG 14):
   • Status of Fish Stocks: The article provides a qualitative but critical indicator by stating that “Chinook salmon stocks in the transboundary Yukon River watershed have collapsed.”
   • Harvesting Regulations: The implementation of a “seven-year moratorium on subsistence harvests of Chinook salmon” is a management action that serves as an indicator of the severity of stock decline.
3. Indicators for Food Security and Livelihoods (SDG 1, 2):
   • Household Subsistence Use: The article provides a direct indicator of food access by citing that “an estimated 51% of households across surveyed Alaskan communities used Chinook salmon (1980–2018) compared to 34% of households since 2019.” This quantifies the impact of fish decline on community food security.

4. Table of SDGs, Targets, and Indicators

Source: nature.com