Wednesday August 24, 2022

Kodiak Daily Mirror

Ever wonder why there are five different species of Pacific salmon — six if you count steelhead — and only one species of Atlantic salmon? It turns out it is because the wild West Coast has been a much more dynamic place to bring up a species.

Genera Salmo, (Atlantic salmon and brown trout) diverged from genera Onchorhynchus (Pacific salmon, steelhead, and western trouts) 15 to 20 million years ago, as the Arctic Ocean began to cool.

Salmon are genetically nimble. An evolutionary event about 80 million years ago essentially doubled the proto salmon’s DNA, allowing them to adapt to changing environments more quickly, and protecting them against localized inbreeding. But Atlantic salmon have not diversified much. That’s because on the east side of our continent things have been geologically stable, relatively speaking, for the past 70 million years.

The western salmon, on the other hand, have faced a far more dynamic environment. Forty million years ago the region that is now the Washington Cascade Mountains was a wide coastal plain. Between 6 million and 17 million years ago basaltic volcanic eruptions flowed like molten rivers across the central Columbia River basin. Tectonic forces lifted up the Cascade, Pacific, and Coast mountain ranges. And the Pacific Northwest endured at least four major ice ages starting about 1.8 million years ago.

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