Stochastic simulation of size variation in turbot: possible causes analysed with an individual-based model

Causes of size variation in a population of juvenile turbot were studied using an individual based model (IBM). Each simulation started with 800 (divided into eight groups of 100 each) 120-day-old (posthatch) juveniles and was run for 140 days, and the data gained from model simulations compared directly with the result of a laboratory study with size-graded turbot. Stochastic growth with memory, which was included in the models as an individual genetical growth rate variation, is important in explaining size variation, and the combination between individual genetic growth rate and social interactions related to size-dependent hierarchies also contributes to size variation. The use of size-dependent growth rate alone fails to explain size variation, and is of little value in predicting size variation in turbot culture. Further, the results indicate formation of different types of size hierarchies for different sizes of juvenile turbot.