Simulation of fish population responses to exploitation

Abstract

A model that couples Larkin's predator-prey model, Ivlev's feeding model, Ursin's growth equation and the exponential mortality model was applied for simulation of the responses of fish populations to exploitation. Simulations were done without food-limited growth, with food-limited growth, with food limited growth and size-specific mortality, and with food-limited growth and age at maturity a function of size. Without food-limited growth there was no compensation for exploitation and the population became extinct with an increase in mortality. With food-limited growth the population compensated for fishing mortality; as abundance decreased, size increased, and production of eggs by the population increased. With either mortality or age at maturity a function of size, compensation was much higher than with food-limited growth alone. Recruitment decreased with increase in exploitation. There was an association between numbers of spawners and recruits, but both the number of spawners and the number of recruits were determined by food limited growth. If age at maturity is a function of size, there are fluctuations in population abundance when fishing mortality is low, but not when fishing mortality is high.