Delay-difference model to estimate the catch of different categories of the western rock lobster (Panulirus cygnus) for the two stages of the annual fishing season

Abstract

The annual exploitation rate of the limited-entry rock lobster fishery of Western Australia is controlled by constraining the total allowable effort. An important aspect of the harvest strategy introduced in 1993 was the use of annual levels of allowed fishing effort that could be varied in accordance with predicted levels of recruitment to the fishery in order to increase the abundance of spawning females and to reduce the variability in the level of annual catch. A model was needed that could examine the impact of alternative management strategies on the 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 over the closed fishing season, is determined from tagging data. Recruitment is estimated from the observed levels of puerulus settlement. The model has been fitted to the observed effort within the southern sector of the fishery. This model allows the evaluation of alternative levels of fishing effort within the management zone, providing managers and industry with a tool to explore alternative harvest strategies.