
A study of king salmon in Alaska, with the focus on the Yukon and Kuskokwim River watersheds, links their population declines to reduced body size and extreme climate conditions in the ocean and in rivers.
Research led by Megan Feddern of the University of Alaska Fairbanks, published in the peer-reviewed scientific journal Global Change Biology in October, notes that king salmon has sustained people in Alaska for at least 12,000 years and until recently, supported the largest subsistence fisheries in the world for the species.
Dramatic declines of king salmon in these two major Alaska river systems led to fishery closures and had a profound impact on rural and indigenous communities. Previous research looked at how climate impacts a few well-studied populations in the region and also how it affects body size.
The researchers compared effects of both climate and body size on a large number of populations through the two river basins. The study makes no mention of any impact on the fisheries from salmon bycatch in the groundfish fisheries offshore of western Alaska.
“We did not look at bycatch effects in this study,” said Eric Schoen, a co-author and a research assistant professor at the university’s International Arctic Research Center. “We focused specifically on effects of climatic conditions in freshwater and the ocean and the body size of adults.”
Schoen also noted that king salmon have been returning to the Yukon and Kuskokwim rivers in smaller sizes for the past 40 years as climate conditions continue to change.
Feddern, a post-doctoral researcher with the UAF’s College of Fisheries and Ocean Sciences, said the project was designed to gain an understanding of how individual populations differ in their response to environmental conditions and identify shared characteristics.
It helps interpret the environment king salmon experience and how it relates to abundance, she explained.
According to Feddern, the size of Chinooks is an important factor in determining the number of offspring produced who survive to adulthood to spawn the next generation.
Researchers used data collected by agencies and tribes to estimate how many salmon spawned each year and the numbers of their offspring that returned to the fishery and spawning grounds.
They cross-referenced more than 30 years of climate data from the U.S. and Canada with 26 different king salmon populations in the region. All the salmon were impacted by extreme conditions, like unusually cold winters and warm summers, during their first year in the Bering Sea.
Other effects were more localized.
When Yukon River temperatures were above average during the spawning migration, fewer salmon returned in the next generation. They noted that river temperature had little effect on the Kuskokwim populations.
Overall, the study found body size had a larger impact than water conditions on Yukon River salmon.