A WSU researcher found salmon mating behavior can reshape rivers, which in turn changes the way the land looks over time.

Lead researcher and associate professor at WSU, Alex Fremier, worked with Brian Yanites, an associate professor at Indiana University, and Elowyn Yager, and a University of Idaho professor, to conduct a study looking at six salmon species and how their mating rituals changed stream beds.

Fremier said the female salmon dig holes and lay eggs in river gravel, male salmon would fertilize the eggs and then the female salmon would rebury them.
“So that’s the sex part,” Fremier said, “she’s digging the hole, that’s the geomorphic effect.”

By digging a hole, the salmon are actually setting up their nests, he said. By unpacking and squeezing the gravel, the bedrock can be exposed and eroded when water levels change.

“They are actually eroding mountains in a much more significant way,” Fremier said.

Researchers have known for a long time, he said, that the act of nest building has a local effect. Fremier said the research they conducted showed biological evolution like salmon speciation, can lead to landscape evolution in a river channel.

In their study, “Sex that moves mountains: the influence of spawning fish on river profiles on geologic timescales,” Fremier and Yanites showed how they formalized the influence of their model over a period of time.

The team researched two models, one looking at the Atlantic and one looking at the Pacific over a 5 million year period.

Yanites said that salmon are very selective of their gravel and gravel size. Different salmon species prefer laying their eggs in different sizes of gravel, he said.

“It’s like having two buckets of popcorn, both are full to the brim,” he said, “ones packed together, and one’s not, if you blow air over the one that’s unpacked more will go out.”

They looked at the mechanics of how the female salmon changed the gravel, Fremier said. For example, a graduate student took a spatula and mimicked a salmon’s tail by shifting the gravel around. He said they also calculated how the size of the gravel along the river dictated where different species spawn.

He said the title of the study and overall concept was conceived in Fremier’s kitchen, Yanites said, over a couple of glasses of wine and beer.

Yanites was the one who created the title of the paper, Fremier said, and there were a lot of jokes over email on this particular project.

“We don’t normally like to go with the catchy title,” he said, “but it seemed appropriate.”