Admittedly, it does sound rather impossible—a fish measuring typically less than a metre long having the power to move mountains. However, we are not talking about just one fish, but millions of them.
Every year, salmon in the millions return to the river or stream where they were born in, to mate and breed. In the process, they build nests in the river bed. As they do so, they fluff the soil and gravel, loosening it.
This simple domestic act, multiplied a million or so times, is enough to change the stream’s profile.
According to Alex Fremier, associate professor in Washington State University’s School of the Environment, “The salmon aren't just moving sediment. They're changing the character of the stream bed, so when there are floods, the soil and gravel is more mobile."
Subsequently, the profile of stream beds are altered, thereby affecting the evolution of the entire watershed. “Any lowering of the streambed translates upstream to lower the entire landscape,” said Fremier.
He, together with colleagues from University of Idaho and Indiana University, were able to model the changes over five million years. They saw how stream slopes and elevations were lowered over time, how the land alongside the stream got steeper and more prone to erosion.
They documented their discoveries in a paper recently published in the Geomorphology journal.
During their research, the scientists also discovered that not all fish species had the same effect; Chinook salmon were able to affect bigger pieces of material while the slightly smaller coho salmon had relatively less impact. The effects of these differences will lead to different erosion rates and landscape changes.