January 4, 2022 — They’ve been pushed to the brink of extinction by dams, drought, extreme heat and even the flare of wildfires, but now California’s endangered winter-run Chinook salmon appear to be facing an entirely new threat—their own ravenous hunger for anchovies.
After the worst spawning season ever in 2022, scientists now suspect the species’ precipitous decline is being driven by its ocean diet.
Researchers hypothesize that the salmon are feasting too heavily on anchovies, a fish that is now swarming the California coast in record numbers. Unfortunately for the salmon, anchovies carry an enzyme called thiaminase, which breaks down thiamine—a vitamin that is essential to cell function in all living things.
“These are fish that returned to the river early this year and then spawned in the spring and early summer. They had really low thiamine,” said Nate Mantua, a fisheries researcher with the National Marine Fisheries Service in Santa Cruz. Concentrations were “worse than last year.”
In humans, a critical deficiency of thiamine, or vitamin B1, can lead to heart failure and nerve damage. In female salmon that are returning to rivers and streams to spawn, thiamine deficiency can be passed on to their many hatchlings, which suffer problems swimming and experience high rates of death, researchers say.
Now, with government agencies and Native American tribes fearing the collapse of the winter-run Chinook, scientists are embarking on a campaign to determine why the anchovy population has exploded off the California coast, and why winter-run Chinook are seemingly ignoring all other prey.
“The very unusual thing about their diet is that it’s been so focused on anchovies and so lacking in other things that historically they have been found eating,” Mantua said. “It is something we don’t have great information on.”