Columbia River chinook salmon have lost as
much as two-thirds of their genetic diversity, Washington State University
researchers have found.
The researchers reached this conclusion after
extracting DNA from scores of bone samples — some harvested as many as 7,000
years ago — and comparing them to the DNA of chinook currently swimming in the
Snake and Columbia rivers.
Writing in the journal PLOS One, the
researchers say their analysis “provides the first direct measure of reduced
genetic diversity for Chinook salmon from the ancient to the contemporary
The researchers found no specific cause for
the decline. Possible impacts, they say, include heavy native fishing pressures
at falls along the Columbia, intensive fishing in the wake of European
settlement and the arrival of dams.
big question is: Is it the dams or was it this huge fishing pressure when Europeans
arrived?” said Bobbi Johnson, who did the study as part of her WSU doctorate in
biological sciences. “That diversity could have been gone before they put the
Johnson’s co-authors are Gary Thorgaard, a WSU
emeritus professor of biological sciences, and Brian Kemp, a former WSU
molecular anthropologist and ancient DNA expert now at the University of
Oklahoma. The researchers also worked with the Spokane and Colville tribes,
associated agencies and Stan Gough, director of Archaeological and Historical
Services at Eastern Washington University.
The researchers started with a trove of 346
vertebrae drawn largely from ancient garbage piles, or middens. Wearing not one
but two layers of medical gloves to avoid contaminating samples with their own
DNA, the researchers gleaned sequences of mitochondrial DNA from a region
shared by 84 of the ancient fish.
“It’s like a little snapshot that tells you
who’s who, who’s in what family or what lineage,” said Johnson.
She then compared these with the same
identifying regions on 379 contemporary samples.
“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 researchers were surprised to see a big
difference between the diversity of contemporary Columbia and Snake River chinook.
On the upper Columbia, two-thirds of the chinook genetic diversity has been
lost. On the Snake, one-third has been lost
While the researchers looked at ancient chinook
DNA from the Spokane River, there are no contemporary chinook for comparison as
construction of the Little Falls Dam in 1911 blocked their migration, Johnson
However, she said, the researchers found the
ancient group had a large number of lineages, six, “and a diversity higher than
any single-stock fishery in the contemporary Columbia sample.”
Northwest Native Americans have caught chinook
for more than 9,000 years, often around natural barriers like waterfalls that
served as bottlenecks for the salmon’s prodigious runs.
Europeans were quick to exploit the fishery
after arriving in the 1860s, and between 1889 and 1922 they harvested as many
as 25 million pounds a year.
That declined to 15 million a year over the
middle of the 20th Century and now stands at less than 5 million, the
The Rock Island Dam, the first on the main
stem of the Columbia, was built in 1933, followed by the Bonneville Dam and the
Grand Coulee Dam, in 1941, blocking ocean-going salmon from more than 1,000
miles of the upper Columbia. Dams on the Snake came more than a decade later.
The Columbia River Basin now has more than 400
dams, the researchers write, blocking more than half the river system’s
If the researchers were to tie a loss of
diversity to market fishing or dam construction, they would need the DNA of
fish from those periods. However, they were unable to draw workable DNA from
salmon tissues preserved during the commercial fishing or dam-building eras.
Their youngest ancient DNA sample was from a 150-year-old sample caught near
Kemp, Johnson’s co-advisor with Thorgaard,
said the study’s findings provide a baseline for what existed in the past and
can inform discussions on the difficult task of bringing stocks back.
“This study serves as a tool for conservation
genetics,” he said.
Funding for the study was provided by
Washington Sea Grant, the Northwest Scientific Association, Washington State
University Elling Research Endowment, a NASA Space Grant Fellowship and the
Palouse Audubon Society.