Closed seasons and tropical penaeid fisheries: A simulation including fleet dynamics and uncertainty

Seasonal fishery closures are commonly used in fisheries management for various purposes, including limitation of effort, protection of spawners, and maximization of the yield or value that can be obtained from a cohort. The effectiveness of a proposed closure can be evaluated through yield-per-recruit analysis, which can be carried out analytically for some simple situations. For other fisheries, such as the penaeid shrimp fishery of Torres Strait, Australia, investigated here, the analyses are more complex because recruitment occurs in pulses throughout the year and the intensity of fishing is itself unevenly distributed in time, being patterned after these recruitment pulses. Furthermore, the imposition of closures of different durations has been documented to alter the pattern and intensity of fishing after the fishery reopens. In this study, a simulation approach is used to identify the timing and duration of closures that are likely to increase the yield or the value per recruit of the fishery. The simulation allows for changes in the distribution and magnitude of effort directly caused by the closures. All input parameters are assumed to be known precisely, except those controlling fishing and natural mortality, which are drawn from empirically derived ranges. The simulation results indicate that a 6-month closure starting in December or January could increase the value of the fishery by 5–10%, compared with a fishery with the same fishing pattern and no closure.