All The Fish

Life After Death: Your Ultimate Guide to Zombie Salmon

after spawning, pacific salmon die. This photo shows a carcass
With death, life begins for the next generation of Pacific salmon. Photo courtesy FISHBIO

Set in motion at birth, the fate of Pacific salmon is like clockwork: each year a new generation returns from sea to spawn. Then, death.

two sockeye salmon skeletons
Sockeye Salmon pair, Kenai National Wildlife Refuge. Photo: USFWS/Katrina Liebich

Pacific salmon spawn only once per lifetime. As they make their final journey home, their silver sides blush as pigments that give their flesh its appetizing red hue move to their skin. The fat that mottles their tasty fillets burns up as females become vessels for plump, fatty eggs — for both sexes, fat stored in their muscles and livers is totally used up by the time they reach the spawning grounds. They grind their tails into the gravel, hoping to make deep-enough nests that withstand the scour of ice and spring floods. Males tap into their reserves to grow fearsome teeth and hooked upper jaws that they use against each other.

sockeye salmon fight on the spawning grounds
Battle-scarred Sockeye Salmon fight visciously for mates in Alaska’s Kenai River. Photo by Kentaro Yasui

The changes salmon undergo near the end of their life are profound and system-wide, including the eventual widespread deterioration of internal organs.

diagram showing the progression of deterioration that salmon go through as they initiate spawning
decaying chinook salmon that are still alive
Chinooks, on the move, begin to show the obvious signs of decay. Photo: Katrina Liebich

The Living Dead

When the frenzy’s all said and done, they’re spent, their fate sealed. It’s a matter of days, a couple weeks at most.

a decaying chinook salmon still alive
A Chinook Salmon kills what limited time it’s got left. Photo: USFWS/Jan Boyer
a decaying sockeye salmon still alive
A spent Sockeye Salmon lurks under the surface of Alaska’s Kenai River. USFWS/Katrina Liebich

We found a fish that was most certainly dead — huge chunks missing, badly decayed, an eye gone — but when we picked it up, it was decidedly NOT dead, and took one last opportunity to spawn all over us! Zombie fish!— @greatlakescisco

Life After Death

Just as they feed the masses when they’re alive, salmon continue to give life long after they’re dead. When the bears are satiated and the fisherfolk have gone home, others partake. Eyeballs, a sumptuous morsel for beaked scavengers, are often the first to go. Depending where the carcasses lay, they’re fodder for fly larvae and aquatic grazers like caddisflies. In an odd twist of fate, these same insects will feed the new generation of salmon incubating beneath the gravel.

A brown bear eating a rotten dead salmon
Trick or Treat? Photo: USFWS/LIsa Hupp
decaying salmon covered in maggots
Where the water ends, the maggots begin. Photo: USFWS/Dan Rinella
decaying salmon covered in maggots
Fly larvae chow a dead Sockeye Salmon in Little Meadow Creek, Alaska. Photo: USFWS/Katrina Liebich
decaying salmon covered in caddisfly larvae
Caddisfly larvae colonize a decaying salmon. Photo: USFWS/Dan Rinella

Many carcasses, snagged by fallen trees, stay put or don’t stray far. Others make their way up and over the banks of the rivers and into the woods and meadows, helped along by wildlife and high flows. Here, in perhaps a stroke of genius, the salmon feed trees that provide shade and, when they fall in, habitat for their offspring and snags to keep carcasses in place [more on this: The Quiet Love Affair Between Fish and Trees].

Some slip past, making it back to sea where they will give back some of the marine nutrients they used to fuel their upstream migration.

decaying salmon covered in amphipods
Amphipods give new life to a salmon at the mouth of Kodiak Island’s Buskin River. Photo by Stephen Jewett
decaying salmon eyeballs removed
A feathered scavenger leaves evidence of its presence on a salmon carcass alongside Kodiak National Wildlife Refuge’s Uganik River. Photo: USFWS/Lisa Hupp

Salmon Graveyards: a good thing

The rhythmic coming and going of salmon graveyards in streams all over Alaska and the Pacific Northwest is a natural (albeit sometimes slightly ghoulish) phenomenon.

salmon graveyards
Where salmon runs have declined or been lost, the graveyards stand empty. In some cases, salmon zombies are being returned to rebuild the nutrient deficit and help scientists learn about the important interaction between salmon zombies and their environment. Photo courtesy Matt Kaylor

Katrina Liebich is the Digital Media Manager for the U.S. Fish & Wildlife Service in Alaska @Liebichthy. Follow us on Facebook and Twitter!

In Alaska we are shared stewards of world renowned natural resources and our nation’s last true wild places. Our hope is that each generation has the opportunity to live with, live from, discover and enjoy the wildness of this awe-inspiring land and the people who love and depend on it.

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