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.