DELAY-DIFFERENCE MODEL TO ESTIMATE THE CATCH OF DIFFERENT CATEGORIES OF THE WESTERN ROCK LOBSTER (PANULIRUS-CYGNUS) FOR THE 2 STAGES OF THEANNUAL FISHING SEASON

The annual exploitation rate of the limited-entry rock lobster fishery of Western Australia is controlled by constraining the total allowabl e effort. An important aspect of the harvest strategy introduced in 19 93 was the use of annual levels of allowed fishing effort that could b e varied in accordance with predicted levels of recruitment to the fis hery in order to increase the abundance of spawning females and to red uce the variability in the level of annual catch. A model was needed t hat could examine the impact of alternative management strategies on t he catches both within and between fishing seasons. The model that has been developed uses a delay-difference structure in which the fishing season is divided into two periods. Growth between the periods, and o ver the closed fishing season, is determined from tagging data. Recrui tment is estimated from the observed levels of puerulus settlement. Th e model has been fitted to the observed effort within the southern sec tor of the fishery. This model allows the evaluation of alternative le vels of fishing effort within the management zone, providing managers and industry with a tool to explore alternative harvest strategies.