Looking for Chinook in the Chena

The Chena River is the second-most productive spawning ground for Chinook (king) salmon in the Yukon River Basin.* The mainstem river and its many connected sloughs and tributaries provide a good mix of warmth, food and shelter for juvenile salmon to feed and grow in a protected area before they migrate out to the ocean. 

Over the past two decades, Yukon River Chinook salmon populations have declined, severely limiting subsistence fishing and cherished cultural traditions. Erik Schoen, a research associate professor at the University of Alaska Fairbanks International Arctic Research Center, leads a team working to understand why salmon populations have declined and how freshwater habitats and food webs are responding to climate change and human development. 

This summer, the team began a new project to improve salmon habitat maps by visually counting fish from jetboats and monitoring environmental DNA (eDNA) in water samples to determine whether salmon are present in an area. The team is documenting how salmon DNA concentrations in the water correspond to known levels of salmon abundance and proximity to the spawning grounds. 

In related projects, the team is also testing whether eDNA tools can detect a common parasite (Ichthyophonus), which can cause pre-spawn mortality in salmon. They are also analyzing the stomach contents of predatory fish, like pike, to identify hotspots where predators are consuming salmon fry. They also measure water temperature to understand how temperature affects where fish spawn and rear.

By working with partners like the Alaska Department of Fish and Game, Tanana Valley Watershed Council, and Yukon River Drainage Fisheries Association, the UAF team can include data from larger study areas. On the Chena River, for instance, the researchers took water samples and counted salmon above the first bridge on the upper portion of the river and Fish and Game researchers made coordinated measurements below the first bridge. This shared effort helps both groups gain a broader view of the core salmon spawning grounds and lesser-used peripheral areas. 

The researchers plan to develop maps that complement existing tools like the ADF&G Anadromous Waters Catalog, which provides legal protections for habitats used for spawning, rearing, or migration by anadromous fishes like salmon. New maps showing estimates of the relative productivity or potential value of different habitats will help prioritize effective restoration efforts, such as replacing fish-blocking culverts, to maximize ecological benefits per dollar spent and streamline environmental permitting while avoiding critical salmon habitats. 

Sampling for eDNA on the upper Chena River: Maggie Harings and Will Samuel, research professionals in the Schoen Lab, left; Erik Schoen and Claire Thelen from the University of Alaska Museum of the North, right.

The habitat mapping project is funded by the Department of Defense Readiness and Environmental Protection Integration Program and the National Fish and Wildlife Foundation. The environmental teams at U.S. Army Garrison Alaska at Fort Wainwright and Eielson Air Force Base support and closely coordinate the fieldwork. 

The Alaska Climate Adaptation Science Center also provides funding for the study involving salmon predators and water temperatures, and UAF provides internal funding for research on the Ichthyophonus parasite. 

*The Salcha River is the most productive river in the Yukon River Basin for king salmon spawning grounds.