Every other week, the Outside/In team at NHPR answers a listener's question about science and the natural world. This week's question comes from Amelia on Instagram.
“Are there any real life zombies?”
Host Nate Hegyi looked into it.
This transcript has been lightly edited for clarity.
Nate Hegyi: I have seen a zombie. It was fall and I was fishing in southeast Alaska. There was this salmon laying out on the rocks next to a stream. It stunk. Its skin was falling off. It literally had no eyes. Just empty sockets. It looked like it was rotting. But then, it started moving — because it was still alive. Turns out, this was what is literally known among biologists as a "zombie salmon."
Daniel Teskey: So, zombie salmon essentially are post-spawn salmon that are essentially eating themselves from the inside out.
Nate Hegyi: That’s Daniel Teskey. He’s a fish biologist with Alaska’s Department of Fish & Game. He told me that salmon are one of a handful of animals out there that act a lot like the walking dead.
Daniel Teskey: It definitely depends on your definition of what a true zombie is, but there are some parallels that you can find in nature.
Nate Hegyi: So let’s say our definition of a zombie is the fungal infected zombies of the HBO show the Last of Us. There is a real world fungus that can infect carpenter ants. It overrides their behavior, makes them climb a plant and lock their jaws onto its stem. Then the ant dies and the fungus grows on the plant.
But the Pacific salmon is perhaps the one that most resembles a classic walking dead, Hollywood zombie, at least physically — though it’s not technically dead.
Daniel Teskey: It looks very, very scary and ugly. And it can be quite shocking. And I can see why people would kind of parallel that with the Hollywood definition because they do look like they're living dead, literally.
Nate Hegyi: Salmon are born in a stream, then they swim out to live in the open ocean for a few years, and then they return to that same stream to breed and die. And that return journey is unbelievably grueling.
Daniel Teskey: And as part of that process, they completely stop feeding and they put all of their energy into reproduction.
Nate Hegyi: They’re beating their way through the water, often in streambeds not even deep enough to cover their bodies. All the while dodging bear claws and eagle talons, and then ripping up their bodies against river rocks.
But they’re no longer eating. So, they need to power their journey in other ways. Like, by reabsorbing nutrients from their own bodies — again, eating themselves, from the inside out — and utilizing a hormonal spike of cortisol.
But that comes with a very rough side effect. It completely suppresses their immune system. So, when they cut themselves on those river rocks, they can’t really heal and they quickly become infected, including by one particular fungus that will attack the eyes, blinding them and even making their eyes fall out.
But I should say this annual zombie salmon invasion is not apocalyptic. In fact, it’s the exact opposite. It is the lynchpin for a healthy ecosystem in many parts of the Pacific Northwest.
Daniel Teskey: The salmon that do spawn and then die provide a whole bunch of marine-derived nutrients to the freshwater systems for invertebrates, other fish, even feeding the trees.
Nate Hegyi: Researchers have found that up to 70% of the nitrogen and other nutrients in the soil near these creeks come from dead zombie salmon.
To submit your question to the Outside/Inbox, leave a voicemail on our hotline. The number is 1-844-GO-OTTER. And remember, Outside/In is a podcast, available on Apple Podcasts, Spotify, or the platform of your choice.
