Computer Simulation of Fisheries Closures

R. Watson, C. T. Turnbull, (1997). 405-410.   Paper published in proceedings of the Developing and sustaining world fisheries resources: the state of science and management. Proceedings of 2nd World Fisheries Congress., Brisbane Australia, Aug 1996

Simulation modelling was used to examine the benefits of seasonal and spatial closures of two prawn fisheries which differed in their recruitment patterns, one had a single recruitment pulse (annual) while the other had two each year (biannual). An optimization procedure was used to assign monthly fishing effort (within realistic constraints) which would maximize annual catch value. Reductions in values resulting from uncertainty in recruitment timing were examined. An ‘ideal’ pattern of monthly fishing effort for each fishery was fitted using an exhaustive search method because other methods could not find the global optimimum. Catch values resulting were used as a basis of comparison within each fishery with closure results. For the annual fishery, the best seasonal closure produced 98% of the value of the ‘ideal’, spatial closures 102%, and combined seasonal and spatial closures 104%. Relative values for the biannual fishery were similar except for combined closures which produced 116%. Generally, however, spatial closures outperformed combined and seasonal closures when recruitment timing was uncertain. Egg production was generally 30-40% of an unfished stock and was highest for combined closures.