Hjort's Forgotten 90 Percent: Early Life Mortality Research in the 21st Century

Johan Hjort’s idea that survival during early life controls year-class strength transformed fishery science in the 20^th century, when management was based on populations. Ensuing research focused on the small percentage offspring that survive - 10% of eggs and 1% through the larval period. Fishery management in the 21^st century has moved toward an ecosystem-based approach, which requires us to consider the fate of the eggs and larvae that do not survive. These forgotten 90% of eggs are mostly consumed by other organisms. Spawning fishes create rich but patchy nutritional resources, which we call “egg boons.” We argue that egg boons are a major trophic pathway and one of the few pathways counter to the main direction of trophic flow. Their limited spatio-temporal availability suggests they could represent a significant trophic opportunity or bottleneck. Egg boons transport nutrients across ecosystems through advection of eggs or spawning migrations. Recognizing the significance of egg boons reveals linkages and feedback loops between organisms and environments that have important implications for understanding how food webs vary in time and space. We discuss examples that illustrate top-down, bottom-up, and lateral control mechanisms that could significantly alter food webs through their effects on planktonic eggs.