The Mystery of the Dead Coho Salmon
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What mystery surrounds the dead Coho salmon?
You're listening to Shortwave from NPR. Hey, Shortwavers. Camila Dominovsky here in the host chair with a mystery. A decades-long puzzle centering on a string of inexplicable deaths. The victims were coho salmon showing up dead in urban streams in Puget Sound around Seattle today. in very suspicious circumstances.
Who is investigating the deaths of the Coho salmon?
That's Zhenyu Tian, whom you might call one of the lead detectives on this case. He was a postdoc research scientist at the Center for Urban Waters at the University of Washington-Tacoma
when he was called in to the case. These fish spawn in freshwater, strike off for the open seas, trek back to the place of their birth, but then they die before they can spawn. And this keeps happening for years.
What are the potential causes of salmon mortality?
If this trend continues, they might be extinct in a few decades. So that's the problem we want to solve.
And we was a lot of people. Biologists, modelers, community scientists, environmental chemists. Some researchers rule out all the obvious culprits. Temperature, oxygen, known toxins. It's none of those. They need a lead.
How did researchers narrow down the suspects?
So I think the first big step is our collaborators, NOAA and the Washington State University.
They look through the data about where fish were dying and started running models.
They are getting this important clue that the mortality risk of coca salmon is related to traffic.
What role does traffic play in the salmon deaths?
Traffic. It's something to do with the roads, the urban runoff. So after years of work, the list of suspects is narrowing, but what part of the runoff? Enter another team of scientists from the University of Washington, including Zhen Yu. They're testing chemicals in runoff.
For example, things from the concrete, things from the antifreeze, like tire particle leachate, and compare the chemistry of those things versus the water that kills coho salmon. Based on that comparison, we see that, okay, tire particle leachate is very similar to that.
What did the scientists discover about tire chemicals?
Smoking gun. It's coming from tire particles. But tires have tons of chemicals in them, and they need to find which one is the culprit. So today on the show, how a team of researchers finally cracked the case of the coho salmon, and how their discovery is having ripple effects. I'm Camilla Dominovsky, and you're listening to Shortwave, the science podcast from NPR.
So knowing that tires have tons of chemicals in them that would need to be narrowed down, Zhenyu and his team step in and start testing batches.
You can think of this as cutting a loaf of bread, right? Like you cut them into thin slices. You have something abnormal in the bread, but you don't know where it is. So by cutting into slices, you can test each slice individually so that you can narrow down the scope from like hundreds to tens to one. That's the logic.
And one by one, they narrowed down the options until they found the deadly chemical. But that chemical, whatever was killing the salmon, it wasn't a tire additive. It didn't match anything put into tires. They still had no idea what it was. So Zhenyu and his team were stuck. They'd zeroed in on this chemical killing the salmon. They knew it came from the tires somehow, but it just didn't match any tire additive. Zhenyu says, yeah, that's the scientific process for you.
You are trying different possibilities, trying different assumptions, and the assumption for additive just didn't work.
Okay, new assumption. If this wasn't a chemical added to tires, maybe it's a chemical that's produced when a tire additive reacts with something. Chemists call that a transformation product. But how do you find that? They were kind of stuck for months until Genu had an idea. Now, at this point, it was 2020. The pandemic had started.
We are not allowed to work a long time in the lab. So I was like running a little bit more and taking a shower. And that's kind of like where, yeah, got that.
Wait, you literally had the idea in the shower?
Yeah. I probably should start that morning run again, but I don't have time for now.
Genu's boss, if you're listening, give this dude some more time to take runs. But anyway, this was his eureka moment. During his post-run shower, the location of so many great ideas, he realized how to find the additives.
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Chapters
8 chapters
1
What mystery surrounds the dead Coho salmon?
0:00–0:27
2
Who is investigating the deaths of the Coho salmon?
0:27–1:06
3
What are the potential causes of salmon mortality?
1:06–1:30
4
How did researchers narrow down the suspects?
1:30–1:49
5
What role does traffic play in the salmon deaths?
1:49–2:27
6
What did the scientists discover about tire chemicals?
2:27–5:15
7
How did a shower lead to a breakthrough in the investigation?
5:15–6:15
8
What is the significance of transformation products in this study?
6:15–11:45