This is a photo of scientist man Alex Fremier, the man behind the study.
The sex lives of salmon are a largely private affair.
That’s an advantage of living underwater. However, an up close look at the way salmon get busy has at least one researcher convinced those trysts may play a surprisingly large role in the evolution of mountainscapes and their associated watersheds.
A study conducted by a Washington State University researcher named Alex Fremier has been attracting attention due to its unlikely premise. Fremier’s work has shown a connection between the reproductive habits of salmon and the way that rivers flow. Fremier says that when salmon stir up river bottom sediment by doing the underwater polka, debris then becomes more susceptible to downstream erosion during high flow events.
The study is one of the very first to quantitatively show that salmon can shape the layout of the land around them.
“The salmon aren’t just moving sediment,” said Fremier, the study’s lead author and associate professors in the WSU School of the Environment. “They’re changing the character of the stream bed, so when there are floods, the gravel is more mobile.”
Female salmon are known to disturb the soil and gravel on the river bottom with their tails during mating activity. That underwater manicuring allows the female salmon to lay eggs into a safe pocket of the river or stream bed where a male salmon follows up to finish the fertilizing business. After that sediment is disturbed, the surrounding stream gravel is more easily moved downstream, which ultimately leads to exposed bedrock and erosion.
Fremier and his project colleagues created a model to replicate changes to watersheds over a 5 million-year timeframe. Over time, the streams with spawning salmon populations began to show lowered stream slopes and elevation.
The land adjacent to those waterways also showed a tendency to become steeper and more prone to erosion.
“Any lowering of the streambed translates upstream to lower the entire landscape,” said Fremier.
Fremier’s study noted that different salmon species can alter their habitat in different ways. For instance, bigger Chinook, or king salmon, are able to displace larger material, whereas coho salmon tend to move smaller debris. Over the course of time, and as those species create specific strongholds on particular watersheds, the diverse populations can lead to different erosion rates and associated changes to the surrounding landscape.
Fremier noted that much attention has been paid to the way that geology can impact wildlife, but relatively little effort has been made to understand the opposite. This study provides an alternate perspective for the role that living things play in the creation of their own habitats.
Just as the presence of salmon can affect the evolution of a watershed, their absence can also lead to changes over time. Fremier has noted that watersheds where salmon drop significantly in numbers or disappear altogether could be subject to significant long-term changes in their nature.
“The evolution of a watershed can be influenced by the evolution of a species” Fremier said.
The study, titled “Sex that moves mountains; The influence of spawning fish on river profiles over geologic timescales,” was published in the journal Geomorphology. The work was conducted by Fremier with help from colleagues at the University of Idaho and Indiana University.
