It turns out that when the humble salmon has sex, the Earth literally moves. New research has found that the stalwart fish has the power – over millions of years – to move mountains and alter the geology in the regions they spawn, and could even be contributing to the evolution of new salmon species themselves.
The migrating fish swim the length of the waterways in order to spawn up stream of the rivers. While the salmon don’t technically have sex in the messy way us mammals manage it, it is the process conducted by the females as they fluff up the sediment and gravel on the stream beds that is thought to lead to the altering of entire mountainsides.
The researchers modeled the impact that this movement of sediment has on the rock that forms the landscape over a period of millions of years, and found that it physically altered the underlying geology of the regions in which migrating salmon spawn. The creating of these “nests”, also known as redds, by the female fish to lay their eggs leads to the lowering of elevation of the slopes on which the streams appear, as well as land alongside the waterways getting steeper and more prone to erosion.
The researchers suspect that the loosening up of the sediment and gravel in order to form the depressions mean that when the stream next floods, the fine particles are more likely to be washed away downstream.
“The salmon aren't just moving sediment,” explained Alex Fremier, who led the research published in the journal Geomorphology. “They're changing the character of the stream bed, so when there are floods, the soil and gravel is more mobile.” This exposes the bedrock underneath, which in turn is more vulnerable to erosion over time.
What’s more, while spawning, different salmon species behave in different ways, and this also has an impact on how the fish impact the mountains and geology of the environment. The authors show that the bigger Chinook salmon, which is the largest Pacific species of the fish, can move larger bits of gravel than the much smaller coho salmon of the same region, and as a result causes much faster erosion of the landscape over the same period of time.
The work feeds into a growing understanding how groups of species, or even individual species themselves, can cause profound changes in the environments in which they live. From wolves changing the course of rivers, to the evolution of trees creating entirely novel landscapes 300 million years ago, it shows the astonishing importance that a single organism can have.
What’s more, the researchers even suggest that the altering of geology and moving of mountains by the mighty salmon could even spur on the evolution of new species of the fish.
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