Scientists working to uncover mystery of disappearing salmon population in Pacific Northwest
After decades of research, it’s a statement that may shock you: "We really don’t know what’s going on out there."
That statement came from Dr. Laurie Weitkamp after she returned from a long stretch on the high seas aboard the Shimada, a National Oceanic and Atmospheric Administration (NOAA) research vessel.
To be clear, we know a lot about salmon – but as Dr. Weitkamp explained, despite a lot of attention we still have knowledge gaps that new research could fill. That includes why models that once accurately predicted salmon returns are becoming less and less accurate.
"We think these events are occurring on the high seas," explained Dr. Weitkamp, talking about low returns that modeling did not predict. "That’s where this unexpected mortality is."
It’s why what Weitkamp, along with 50+ other scientists, just wrapped up is so important. An international team took part in the 2022 Pan Pacific Winter High Seas Expedition with the International Year of the Salmon.
The dozens of scientists spent weeks in the North Pacific in the middle of the winter. The work is difficult – often times hundreds of miles from shore and in rough conditions. While in the North Pacific, scientists caught salmon, and collected thousands of data points.
While research on the high seas stretches back to the early 1900s, there are challenges that prevent scientists from getting a full picture. Aside from the conditions, crews typically have two choices: heavily research a small area, or cover a lot of area but perform less research.
This particular expedition changed things in terms of size and scope of how research can work. Scientists from Canada, Japan, the Republic of Korea and Russia joined Americans – meaning they could deploy multiple ships to cover a wider area without sacrificing granular detail.
"There’s so much to learn, and part of it is just the challenge to get out on the high seas to sample out there," explained Marisa Litz, a WDFW research scientist who was on the Shimada for part of this year’s International Year of the Salmon expedition. "We’re looking at a critical life stage where – despite 100 years of salmon research – we really don’t have a lot of information. This stage is sort of like a ‘black box.’"
In recent years as salmon stocks decline, hatchery production has exploded in an attempt to bring back the large number of salmon our region once saw. As Litz pointed out, we are putting more salmon into the North Pacific – but we are seeing poor returns for some species.
Salmon vary by species but in general, they follow a similar trajectory: born in freshwater salmon hatch from eggs and begin to grow-up in freshwater streams and rivers. At a certain point, they begin their journey out of their streams and into the open ocean before they follow ancestral patterns. Depending on species, they spend a different number of years in the ocean before returning to the exact location they were born to spawn, and eventually die – the cycle continues with their offspring.
A majority of life for salmon are spent in marine waters – despite a lot of attention on nearshore habitat, and restoration of rivers to ensure salmon can make it to the ocean, scientists still expect up to 90% of juvenile salmon will die in the ocean. Many, within the first few months.
That does not mean habitat restoration is not important – without that work, fish wouldn’t survive long enough to make it to the ocean. However, the lack of salmon who make it to the open waters that eventually return speaks volumes to the complicated web of issues that Washington’s endangered species face.
As Weitkamp explained, the conditions of the ocean are changing at the same time we’re seeing crazy swings in the abundance of salmon population. At a time that climate change and marine heat waves like the infamous "blob" add additional challenges, it’s important that we understand what salmon are dealing with: what prey is available to eat, what predators are preying on salmon, and how is the eco-system supporting – or harming – salmon?
"We don’t really have a good understanding of how uniform the ocean is out there," said Dr. Weitkamp. "This study helps us understand a lot of that."
While the work on the water is wrapping up, the work on land is just beginning.
In the coming months scientists will be able to identify which salmon were caught in various parts of the ocean, and using DNA identify which river systems they come from – that can be cross-referenced with the data they collect on the eco-system, and the conditions they’re in at the moment of capture.
Data collected by various countries will be shared, cataloged, and used for dozens of research projects. That work will ultimately unlock new information to better forecast and manage salmon populations with an end goal to build resiliency for salmon.
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