Chinook salmon, an iconic species in the Pacific Northwest that supports a major fishery industry and indigenous traditions, have lost up to two-thirds of their genetic diversity over the past 7,000 years, according to a new study. Scientists warn the loss could make it difficult for the species to cope with warming global temperatures and ocean acidification — environmental changes that are already impacting the fish today.

Scientists from Washington State University and the University of Oklahoma worked with several Native American tribes to get access to Chinook salmon bones from archaeological sites and ancient garbage piles dating back 7,000 years. They then analyzed the DNA in 346 historical samples and compared them with 379 samples from modern Chinook salmon. The scientists found that Columbia River Chinook have lost two-thirds of their genetic diversity; Snake River Chinook diversity declined by one-third.

Researchers and conservationists who study Chinook have long suspected the species has experienced a significant loss in genetic diversity. “Science finally caught up with what we already believed and allowed us to test it,” Bobbi Johnson, lead author of a new study, told The Spokesman-Review.

The study, published in the journal PLOS One, attributes the decline to overfishing, stream habitat loss, and the construction of more than 400 dams in the Columbia River Basin. In addition, to help boost the Chinook salmon’s population numbers, every year millions of fingerlings from hatcheries are released into waterways throughout the Pacific Northwest. These hatchery fish, however, are more genetically similar than wild salmon populations.

The question now, Brian Kemp, an ancient DNA expert at the University of Oklahoma and one of the study’s team members, told Science: “Is the environment changing faster than these [salmon] can keep up?”