Improving Salmon Resilience to a Warming Climate

Salmon are the lifeblood of much of Alaska. Extensive river and lake systems protected in Alaska national parks provide significant habitat for all five species of Pacific salmon. However, as the climate warms, rising temperatures may threaten these important salmon resources. This project, made possible by the Bipartisan Infrastructure Law (BIL), will describe reference conditions and potential targets for ecosystem recovery due to climate change, wildfires, oil spills, and other disturbances.

Sockeye salmon in Telaquana River, at the headwaters of the Kuskokwim watershed in Lake Clark National Preserve.

NPS/TOM SAXTON

Annual salmon returns to the Yukon and Kuskokwim watersheds have provided a primary source of food for Indigenous communities for millennia. However, salmon returns to these watersheds have declined for more than a decade, threatening the traditional culture and food security of these communities. Warming water temperatures have been identified as a driver of declining salmon returns. When temperatures exceed certain thresholds (above 64°F or 18°C), it is more difficult for salmon to swim upstream and reproduce successfully, causing heat stress or pre-spawn mortality. In 2019, record-breaking air and water temperatures coincided with widespread mortality of salmon returning to spawn in Alaska. Climate projections indicate the trend of increasing water temperatures is likely to continue in the future.

Mapping cold-water areas that can be a refuge for salmon during their migration will help the National Park Service protect them.

NPS/J. MILLS

Fish can avoid warm water by using cold-water refugia. Cold-water refugia are important freshwater locations typically associated with groundwater inputs (e.g., springs), cooler tributaries, and shaded areas. They provide cooler conditions that offer short-term protection to various species, including salmon.

The effectiveness of cold-water refugia depends on their location, distribution, frequency, connectivity, and persistence. Mapping spatial distribution and characteristics of refugia in a waterbody is a critical step to understand its susceptibility to warming temperatures. This understanding can then inform the development of management strategies to maintain the condition of cold-water refugia in key stream reaches.

Food is another important consideration. Macroinvertebrates (large aquatic insects) are a major food source in aquatic habitats for many types of sport and subsistence fish, including salmon, trout, char, and whitefish. Understanding macroinvertebrate presence, distribution, and diversity is critical to maintaining healthy aquatic systems, particularly with an increasing probability of incidents that could cause stress or negative impacts to fish. Assessments are complicated because shifts in biotic communities and distributions over time are likely, and the effects of shifts will be exacerbated by environmental disturbances (such as wildfires, oil spills, invasive species introductions, etc.).

With funding from BIL, the National Park Service (NPS) will document and assess fish and macroinvertebrate species and their shifts over time in order to make the best conservation decisions. This will require establishing reference conditions and ongoing assessments of biotic communities over long time periods and large geographic areas—especially challenging in the remote environments of Alaska.

Because of this complexity, the NPS is making use of modern biological monitoring techniques, such as the use of environmental DNA, or eDNA. Environmental DNA is DNA that organisms shed into the environment—such as skin cells, feces, and secretions. In aquatic ecosystems, eDNA can be present in relatively large quantities in the water column and sediments.

“Using eDNA to sample is more efficient and cost-effective with greater spatial coverage because we only need to collect water or sediment samples for processing,” said Dan Young, fisheries biologist for Lake Clark National Park and Preserve. “This technique has been shown to be viable in aquatic ecosystems and is a preferred method of environmental assessment in other remote places.”

By collecting this information and increasing our understanding of environmental changes, the NPS can make informed decisions that protect salmon and Indigenous ways of life, restore ecosystems, and respond to climate change.

About the Bipartisan Infrastructure Law

The Bipartisan Infrastructure Law makes critical investments in the resilience and restoration of America’s lands, skies, and waters, and enhances conservation and recreation opportunities. Visitors will see tangible results such as repaired and upgraded trails and campgrounds, removal of invasive species, as well as healthy wetlands, grasslands, and forests.