Spawning season influences on commercial catch rates: computer simulationsand Plectropomus leopardus, a case in point

Spatial and temporal closures of sections of the marine environment are pro posed frequently as fishery management devices, particularly when specific areas, such as spawning aggregations, can be identified. The ultimate effec tiveness of spawning area closures is unknown, as spawning-related determin ants of catch rate have not been studied. A simulation model, based on exis ting biological and fisher information, was constructed to examine the most important determinants of the spawning season catch rates using the protog ynous aggregative spawner Plectropomus leopardus (Family Serranidae, Subfam ily Epinephelinae) as a test case. Model output indicated that spawning sea son catches rose as long as catchability of spawners was equal to or greate r than that of nonspawners. Greatest increases in catch were produced by fi sh moving from habitats inaccessible to fishers into regularly fished locat ions during migrations to spawning aggregations. Elevated catches were not simply dependent on the targeting of aggregations by fishers. Small-scale s patial closures around spawning aggregation sites would not be sufficient t o protect the spawning stock of fish such as P. leopardus, but larger scale closures during the spawning season may be useful even when fishers are no t targeting spawning aggregations.