Night of the Living Dead Salmon

by Kelly Neal and Gabe Saron

Fish 1

Adult Chinook salmon carcass picked up by the Carcass Crew. Photo Credit: Kelly Neal

On a cool and misty morning somewhere south of Redding, California, jet boats roar across the tranquil Sacramento River. Armed with tridents, machetes and poleaxes, it seems akin to a scene from an action movie; except that “California Department of Fish and Wildlife” is painted on the boats. One by one, the boats peel out of formation and hole up in eddies and backwaters beside the main river channel. Then, they wait.

Once a pale shadow is spotted within the murky depths of the riverbed, someone onboard thrusts a trident into the water and sinks its barbed prongs into something fleshy. Then, they raise it back out of the water and pivot the catch toward the bow. Glistening in the morning light, covered in welts and sores with blood streaming, a creature resembling something from a horror films slaps onto the deck. The catch lands on a measuring board and the team flies into action, calling  “Fork length: 870mm, male, spawned, disk tag ready.”

It is an adult Fall Run Chinook Salmon, just past the end of its life cycle. It takes on a zombie-like appearance as it consumes its own body for energy on the journey upstream to spawn. After spawning, the fish died and continued decomposing before crossing paths with the Carcass Crew.

Aboard the jet boats, the fishy bodies are dissected in the name of science. With knives and forceps, researchers extract eyeballs and otoliths (ear stones) from the fish. Putrid carcass residue spills across the bow and splatters the boots and pants of the team. Eyeless and mutilated, the fish is clamped with a metal tag and tossed back into the current. This floating horrorshow is one example of the length that people will go to understand and protect Chinook salmon.

Fish2

Salmon carcasses for dissection.  Photo credit: Kelly Neal

This fish was, despite being slaughtered after its death, one of the lucky ones. It completed its life cycle in a largely hostile landscape: it survived variable ocean conditions, slipped past salmon fishermen, and avoided Delta water diversions on its way upstream to spawn. Something of a feat since only thousands of salmon are able to make the journey homeward now, when millions once did (Gresh 2011). Its tissues bear chemical traces from the waterways and food webs that sustained it across its lifespan. Its metal tag helps researchers compute the total number of returning adults by comparing the number of tagged to recaptured carcasses. This carcass is part of a massive effort to quantify how many spawning adults return, and what helps them survive the long watery journey.

Scientists aren’t the only ones looking for salmon carcasses. All along the Pacific Coast, organisms of all trophic levels, and even the next generation of juvenile salmon, sustain themselves on nutrient-rich carcasses. In Salmon streams in Alaska and the Pacific Northwest, bears and wolves feast on carcasses and carry their leftovers into adjacent riparian forests. This enables trees to uptake the nutrients of decaying fish. Marine-derived nutrients can restructure entire forest ecosystems, and provide nutrient-limited headwaters a pathway for growth (Naiman 2009).

Fish 3

Bobcat feasts on a Chinook salmon carcass on the Sacramento River. Photo credit: Eric Holmes

In California’s Central Valley, much of the water and its nutrients are appropriated for agriculture. In 2018, the Pacific Fishery Management Council estimated 108,000 returning Chinook Salmon adults in California’s Central Valley (Pacific Fishery Management Council, 2019). Assuming the average adult Chinook Salmon weighs 20kg and contains about 5% Nitrogen, Chinook Salmon delivered roughly 126 metric tons of marine-sourced nitrogen fertilizer to the Central Valley last year. Isotopic tracing has shown that these nutrients make their way into wine grapes, and possibly other crops, irrigated from salmon streams (Moyle and Merz 2006). This Halloween, consider something truly spooky: when you prepare a fresh salad or pour a glass of Pinot Grigio, you might be giving second life to the carcass of a long dead Chinook Salmon. Cheers!

Kelly Neal and Gabe Saron are Junior Specialists at the UC Davis Center for Watershed Sciences. 

Further Reading 

Gresh T., Lichatowich, J., Schoonmaker., P. An Estimation of Historic and Current Levels of Salmon Production in the Northeast Pacific Ecosystem: Evidence of a Nutrient Deficit in the Freshwater Systems of the Pacific Northwest. Fisheries 25:1. 2000

Merz, J. and P. Moyle, Salmon, Wildlife and Wine: Marine-Derived Nutrients in Human Dominated Ecosystems of Central California. Ecological Applications 16(3) 2006.

Ogaz, Mollie, The Spawning Dead: Why Zombie Fish are the Anti-Apocalypse, CaliforniaWaterBlog.com October 29, 2017.

Pacific Fishery management Council. Review of 2018 Ocean Salmon Fisheries. 2019.

Pinay, G., O’Keffe, T., Edwards, R., Naiman, R., Nitrate removal in the Hyporheic Zone of a Salmon River in Alaska.” River Research and Applications 25. 2009

About jaylund

Professor of Civil and Environmental Engineering Director, Center for Watershed Sciences University of California - Davis
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