Sardine Operating Model Assumptions Regarding the November Survey

Mathematical models of a population can seldom capture every detail of the population’s biology and life cycle. However, models are designed to provide a fairly accurate picture of typically only one key aspect of the population. The operating model for South African sardine is designed to model the overall population dynamics to give an indication of changes in this overall (one or two stock) population, in contrast, for example, to changes in the population within a particular month (such as from the start to end of a survey) or within a small area. In all models some assumptions are made (and hopefully these are clearly detailed!). The operating model for sardine assumes, inter alia, that all sardine have a birthdate of 1 November and that the November survey provides an estimate of the adult (1+) stock (de Moor and Butterworth 2012). This document explores the pros and cons of these specific model assumptions.