Spatial and temporal changes in egg production in the western rock lobster(Panulirus cygnus)fishery

Abstract

Size at maturity in the western rock lobster (Panulirus cygnus) fishery in Australia increases from north to south and female lobsters carry either one or two batches of eggs per season depending on their carapace length. There has been a steady decrease in the size at first maturity of western rock lobster over the last 30 years, and there are now significantly more small females, many below the legal minimum size, contributing to the brood stock than any time since the fishery has been researched. Biological data were used to show the current contribution to egg production in different management regions of the fishery and historical length-frequency data were used to show how egg production has changed in those regions overtime. Reasons for the change in size at maturity in this fishery are unclear, but the outcome has been that egg production is now more evenly distributed across management zones. Egg production was high at Abrolhos Islands in the 1990s owing to strong year classes of breeding animals entering the fishery over those years. In the period since 2000, egg production has fallen sharply at the islands, but has increased in the coastal population compared with the 1980s and 1990s.

Finding lobsters: investigating a period of unusually low settlement of

“…1). Phyllosoma are first immersed in the ocean between 40 and 100 m (Melville- Smith et al 2009) and, subsequently, driven off the continental shelf by alongshore winds, through Ekman transport, and the region's dominating eastern boundary current, the Leeuwin Current (LC; Phillips et al 1981;Feng et al 2011;Wang et al 2015). The LC eddies retain the larvae as zooplankton while they feed on soft-bodied prey with a preference for chaetognaths (Saunders et al 2012;Säwström et al 2014).…”