Research using Columbia River chinook salmon DNA as old as 7,000 years indicates these fish have lost as much as two-thirds of their genetic diversity.
Scientists at Washington State University said their analysis “provides the first direct measure of reduced genetic diversity for Chinook salmon from the ancient to the contemporary period.”
However, the researchers found no specific cause for the decline. “The big question is: Is it the dams or was it this huge fishing pressure when Europeans arrived?” said researcher Bobbi Johnson. “That diversity could have been gone before they put the dams in.”
Northwest Native Americans have caught chinook for more than 9,000 years, according Washington State University, and Europeans began arriving in the 1860s and harvested as much as 25 million pounds a year between 1889 and 1922.
The “ancient” DNA was drawn from vertebrae taken from garbage piles. This was compared with contemporary samples from the same regions on the Columbia and Snake rivers.
“We found what was long suspected, that there was a lot of genetic diversity present, at least prior to when Europeans arrived,” Johnson said.
The Columbia River Basin has more than 400 dams, the researchers say, “blocking more than half the river system’s spawning habitat.” However, to determine whether market fishing or dam construction caused the loss of diversity, they would need DNA from fish alive during those periods. Unfortunately, their youngest ancient DNA was from a 150-year-old sample caught near Fort Colville.
Fish in the upper Columbia river suffered a decline in two-thirds of the genetic diversity, while on the Snake River that decline was only about one-third. DNA samples were available from ancient chinook from the Spokane River, but there are no contemporary chinook for comparison because the construction of Little Falls Dam in 1911 blocked their migration.
The researchers say this study provides a baseline and can inform discussions on the difficult task of bringing stocks back.
Funding for this study came from Washington Sea Grant, the Northwest Scientific Association, Washington State University Elling Research Endowment, a NASA Space Grant Fellowship and the Palouse Audobon Society.
Fish survival in the region has long been a significant issue, with calls to breach several dams on the Lower Snake River in Washington State to protect threatened and endangered salmon.
HydroVision International 2018 will feature conference sessions on the topic of fish passage.
25 Years of Fish Passage in the U.S.: Does it Work? is one example. Click here to learn more.