WSU Study Shows Big Loss in Historic
According to scientists at Washington State University, the Chinook salmon that inhabit the Columbia River today are swimming in a much shallower gene pool than their ancestors.
Although they are not quite sure why, scientists at WSU are certain that Columbia River salmon have lost most of their genetic diversity over time. A recent study conducted by extracting DNA from bone samples dating back as far as 7,000 years ago showed that the diversity of Chinook salmon DNA currently found in the Snake and Columbia rivers has decreased by as much as two-thirds of their historical abundance.
A report from WSU noted that preserving genetic diversity is one of the primary goals of the Endangered Species Act because it helps species adapt to changing environments. Despite its importance, genetic diversity has rarely been catalogued as extensively as the WSU study accomplished. In the science journal PLOS One, the researchers wrote that their analysis "provides the first direct measure of reduced genetic diversity for Chinook salmon from the ancient to the contemporary period."
A report from WSU added that fishery management typically hinges on four factors known as "The Four H's" -- habitat, harvest, hatcheries and hydropower. The WSU genetics study sought to add a fifth "H" to the equation -- history.
Although researchers were unable to pinpoint a specific cause for the decline, they noted that possible contributing factors could include the introduction of a series of dams on the Columbia and Snake river systems, and increased fishing pressures at falls along the Columbia after the arrival of European settlers.
"The big question is: Is it the dams or was it this huge fishing pressure when Europeans arrived?" noted Bobbi Johnson, who conducted the study as part of her WSU doctorate in biological sciences. "That diversity could have been gone before they put the dams in."
Johnson was assisted in the study by co-authors 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. In order to conduct the study the researchers worked closely with the Spokane and Colville tribes, associated agencies and Stan Gough, director of archaeological and historical services at Eastern Washington University.
Most of the historical samples were located in ancient middens, or garbage piles, left by the region's original inhabitants. In order to collect their cache of 346 vertebrae, the researchers donned two sets of medical gloves in order to prevent contamination of the samples and then 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," wrote Johnson in a report.
Continuing the study, Johnson then compared the historic samples with 379 contemporary samples of Chinook DNA.
"We found what was long suspected, that there was a lot of genetic diversity present, at least prior to when Europeans arrived," said Johnson.
One twist on those findings was the surprising difference in diversity of the Upper Columbia stock compared to Snake River fish. Scientists found that while Upper Columbia River Chinook have lost around two-thirds of their genetic diversity while Chinook on the Snake River have only lost about one-third of their historic genetics.
Additionally, researchers looked at ancient Chinook DNA from the Spokane River, but they were unable to compare it to modern samples because they don't exist. Construction of the Little Falls Dam in 1911 blocked their migration to spawning grounds, but Johnson noted that the historical samples from the Spokane River included six separate lineages "and a diversity higher than any single-stock fishery in the contemporary Columbia sample."
The study noted that Native Americans have been fishing for Chinook on the Columbia River fore more than 9,000 years. Those tribal fisheries often utilized waterfalls and other natural barriers that created a bottleneck in the river in order to increase their catch. When Europeans arrived in the mid 1800's they quickly exploited those techniques for commercial advantage. It is estimated that between 1889 and 1922 European's harvested as many as 25 million pounds a year. By the middle of the 20th century those harvests had declined to around 15 million pounds per year and now sits at less than five million pounds per year.
The Rock Island Dam, the first dam built on the mainstem of the Columbia River, went up in 1933 and was followed by the construction of the Bonneville and Grand Coulee dams in 1941. Those blockages prevented ocean-going salmon from accessing more than 1,000 miles of Upper Columbia River habitat. A decade later dams began popping up on the Snake River and today there are more than 400 dams in the Columbia River Basin. Researchers believe that more than half of the river systems spawning habitat is now inaccessible as a result.
In order to pinpoint blame on market fishing or dam construction researchers would need to obtain DNA from fish that lived during those periods. However, they were unable to extract workable DNA from salmon tissues preserved during those eras. Their youngest historical DNA sample came from a fish caught near Fort Colvile 150 years ago.
According to Kemp, the study still provides a baseline for what genetics existed in the past, which can be used to inform conversations and the decision making process for attempting to recover thost stocks.
"This study serves as a tool for conservation genetics," Kemp said in a report.
The study was funded in part by the Washington Sea Grant, the Northwest Scientific Association, Washington State University Elling Research Endowment, a NASA Space Grant Fellowship and the Palouse Audubon Society.
WSU Research Shows Dramatic Decline in Genetic Diversity of Columbia/Snake Chinook Salmon by Staff, Columbia Basin Bulletin, 1/12/18
WSU Researchers Discover Shrinking Gene Pool Among Chinook Salmon Populations by Chad Sokol, Spokesman-Review, 1/11/18
Dramatic Decline in Genetic Diversity of Northwest Salmon Charted by Staff, Science Blog, 1/11/18
Pacific Northwest Salmon Are in Big Genetic Trouble by Robert F. Service, Science Magazine, 1/10/18
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