New research published by the Washington Department of Fish and Wildlife (WDFW) adds another data point to a long-held theory between temperatures in the Pacific Ocean, and winter steelhead survival along many of Washington’s storied rivers.
WDFW’s study focused on winter-run steelhead (returning to fresh water between November and April) on steelhead rivers off the western edge of the Olympic Peninsula, and a few that flow into Grays Harbor. The Chehalis, Hoh, and Quinault were among the rivers studied.
By looking at data all the way back to the early 1980s, researchers were able to track steelhead abundance, and cross-reference that with temperature readings from the Pacific Ocean, where steelhead spend the majority of their lives.
“Our team’s findings provide evidence that increased temperatures and intensified competition at sea have contributed to negative trends in survival for many steelhead populations, outside of freshwater factors that may affect individual populations,” said Jan Ohlberger, a WDFW research scientist and the study’s lead author in a recent article by WDFW on Medium.
Looking at the specifics, the study found that both immature and adult steelhead survival rates have declined as ocean conditions have changed, leading researchers to believe there’s a “strong” association between the two.
In addition, the researchers also pointed to the abundance of pink salmon (which are bred in hatcheries and released by the millions to supplement the commercial fishery). Pink salmon and steelhead “may compete for prey or otherwise be linked in the marine food web,” the study concludes.
The study then made the claim that “if not for these variables…coastal winter steelhead survival and abundance would have been nearly constant over the last four or five decades.”
WDFW is concluding that if pink salmon populations hadn’t exploded, and ocean conditions hadn’t changed (most notably warming water), steelhead would be as abundant as they were in the 1970s.