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Salmon Diversity Lost

Chinook salmon living in the Columbia River in Washington State have lost about two thirds of their genetic diversity, according to a new PLOS One study.

Researchers from Washington State University examined 346 ancient and 366 contemporary salmon samples from different spots in the Columbia River basin, obtaining the ancient samples, some of which stretched back 7,000 years, from middens.

The Washington State team isolated and analyzed mitochondrial genomes from the fish for comparison. From this, the researchers found that contemporary salmon had decreased diversity as compared to their ancestors. However, the team noted that Chinook salmon living in the Snake River, a tributary of the Columbia River, didn't lose as much of their genetic diversity as the Columbia River fish did. The Snake River Chinook salmon lost a third of their genetic diversity, as compared to the Columbia River salmon's two thirds.

Why the salmon's genetic diversity declined isn't clear, but the researchers say it could have been due to the influx of European settlers and the building of dams on the rivers.

"The big question is: Is it the dams or was it this huge fishing pressure when Europeans arrived?" first author Bobbi Johnson from WSU says in a statement. "That diversity could have been gone before they put the dams in."