Relationships Between Spawning Stock, Environment, Recruitment and Fishing Effort for the Western Rock Lobster, Panulirus Cygnus, Fishery in Western Australia

Abstract

Previous studies have shown that environmental factors, the Lecuwin Current and westerly winds, have a significant effect on levels of puerulus settlement at coastal locations in the western rock lobster (Panulirus cygnus) fishery. However, these environmental factors do not explain an average decrease of 50% in the puerulus settlement at the Abrolhos Is. (on the edge of the continental shelf, 60 km off-shore from the north coastal region) from the 1970s compared with that observed in the last 9 years. During the past 20 years there has been an increase in fishing effort resulting in a marked decline in the spawning stock, particularly in the north coastal region. The stock-recruitment-environment relationships for three sites covering the main regions of the fishery show that environmental effects explain the main fluctuations in puerulus settlement in the coastal sites, Dongara and Alkimos, with the spawning stock not being significant. However, the reduction in spawning stock appears to be the main factor explaining the decline in Abrolhos Is. settlement during the last 9 years. The complementary relationship of recruitment to spawning stock shows that fishing effort two years prior to spawning, i.e., on the recruits to the fishery, is significant in explaining the decline in coastal spawning stock.