It has long been believed by scientists and anglers alike that Pacific salmon stop feeding when they enter freshwater rivers and streams for their annual spawning run. Sure, they take the occasional salmonid egg, but it’s argued that this is done out of instinct or to give their own progeny a better chance against the competition.
According to a study from a group of researchers, all of this “common knowledge” may be just plain wrong.
The study by Shawn R. Garner, John W. Heath, and Bryan D. Neff shows that many species of Pacific salmon not only eat and digest eggs in freshwater rivers and streams, they may actually depend on the nutrition they gain from this to complete their spawning runs.
The researchers checked the stomachs of specimens representing three species of Pacific salmon (chum, coho, and Chinook) collected in four locations and found that 13 percent contained eggs. They further found that the fish were eating up to 14 eggs per day. They believe their findings may be conservative as they found that fish pass eggs in two days, meaning “the prevalence of egg consumption is likely a minimum estimate.”
The researchers also carried out feeding trials on captive fish and found that they were able to covert ingested eggs into energy. Fish fed eggs lost much less body mass than unfed fish.
The full research paper can be read online here.