The Impacts of Environmental Change and Ecosystem Structure on the Early Life Stages of Fish: A Perspective on Establishing Predictive Capacity

Since Hjort's seminal work in the early twentieth century, researchers studying the early life stages of fish have attempted to understand and clarify the roles of growth and loss to help predict patterns of recruitment variability. Estimating the abundance of eggs and larvae has provided a fishery-independent measure of stock spawning potential. We also have significant skills in predicting the drift and dispersal of fish eggs and larvae, and consequently the role of wind-driven circulation on potential losses. However, there are few instances where the role of trophic dynamics on growth, starvation or mortality has been demonstrated without ambiguity. Here, I discuss what research needs to be carried out to establish a predictive capacity about the roles of food availability and predator abundance in determining development, growth and mortality of fish eggs and larvae. Revisiting laboratory approaches to determine feeding capacity and growth potential, as well as the application of advanced sampling methods and analytical approaches needed to develop an understanding of how larvae are affected by prey and predator, are just two issues that represent key challenges that we must address in order to develop rigorous frameworks within which we can make and test predictions about early life-history dynamics. Each year-class represents the outcome of a series of stochastic processes involving many factors. Although the objective of forecasting year-to-year fluctuations in recruitment is unrealistic, the development of a biophysical stochastic framework can serve to forecast probabilities of reproductive success in response to physical forcing and food web structure.