ABSTRACT
Surplus production models (Chapter 11) ignore sexual, size-, and age-based differences by treating a stock as undifferentiated biomass. Even a superžcial consideration of the ecological differences to be found within and between the members of a population suggest that this assumption may be leaving out important in¥uences on the population dynamics. An obvious example would be the time delays present in the dynamics of populations that have a number of years between biological recruitment as juveniles and sexual maturity. In a favourable year, leading to a strong year class, there will be a major increase in stock biomass, but it may take a few years before that biomass starts to contribute to reproduction. By lumping growth, reproduction, and mortality into one production function, dynamic interactions between these processes are ignored.
