Egg Consumption in Mature Pacific Salmon: Consequences for Energetic Models and Fitness in Changing Environments

For over a century conventional wisdom has maintained that Pacific salmon cease feeding when they return to freshwater rivers to spawn. Here, we overturn this belief by showing that multiple species of Pacific salmon consume eggs during spawning. Overall, 13% of stomachs contained eggs and feeding rates were estimated at up to 14 eggs per day. Feeding experiments revealed that mature salmon can digest eggs as fed salmon maintained significantly higher body mass than unfed salmon. Such egg consumption presents a fundamental shift in our understanding of Pacific salmon ecology that may have important implications for migration and management models, especially in the context of changing environments and thermal stress. Indeed, the energy from consumed eggs could allow salmon to migrate up to an additional 2 km upstream per day of feeding, or extend the duration of spawning activity by up to 6%. These energetic benefits were most pronounced in small fish, which consequently are predicted to be most sensitive to changes in egg availability in the river environment. Additionally, salmon stocks may have evolved local adaptations to their specific migration and spawning requirements that include nutrients from salmon eggs. We conclude by discussing the potential effect of climate change on migration timing of pacific salmon species and the feeding ecology on spawning grounds.