Excerpt from On World Water Day, scientists study spawning salmon through a riverbed lens," posted on NSF News, March 22, 2016.
Each year on the United Nations-designated World Water Day, March 22, people around the world consider the importance of fresh water to ecosystems and to us. On World Water Day 2018, the National Science Foundation (NSF) looks at Earth's critical zone -- the realm on our planet's surface between the forest canopy and bedrock -- and the role North America's West Coast rivers play in sustaining spawning salmon.
To find out more about the health of these salmon rivers, NSF spoke with scientists at the Southern Sierra Critical Zone Observatory (CZO), one of nine NSF CZOs across the country, and in NSF's Division of Earth Sciences, which supports the CZOs. Southern Sierra CZO researcher Cliff Riebe of the University of Wyoming and NSF CZO program director Richard Yuretich shared their insights. Answers are by Riebe unless otherwise noted.
Why did you decide to study West Coast rivers and their spawning salmon?
The critical zone's geology and biology are intertwined. The grain size of sediment in rivers, it turns out, helps determine aquatic habitat quality. That has implications for spawning salmon, because bigger sediment particles make it harder for these fish to construct their nests, called redds. Do bigger fish fare better in rivers with larger-grained sediment? The answer involves links between life at the surface and characteristics of the bedrock that lies below.
Where did your research take place?
Our team studied spawning salmon in the Shasta River in California, South Prairie Creek in Washington, and Scotch Creek in British Columbia.
Why did you choose those locations?
Salmon in these rivers and creeks are abundant -- or were when we did our research. The fish were using as much of the riverbed as they could, pushing the limits of the available spawning habitat. There were so many salmon they used even the largest-grained areas, despite the challenges of moving the sediment.
On the Shasta River, there's a population of large Chinook salmon, the biggest of the five Pacific salmon species. The much smaller pink salmon are common in South Prairie Creek. And Scotch Creek supports sockeye salmon, whose size is intermediate between that of the Chinook salmon of the Shasta River and the pink salmon of South Prairie Creek. By choosing rivers and streams that support a range of salmon, we were able to study the relationship between sizes of the fish and the largest sediment particles they can move.
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