Effect of collectors of the puerulus of the southern rock lobster Jasus edwardsii (Hutton, 1875) (Decapoda: Achelata: Palinuridae) on lobster catch rates in Tasmania, Australia

Abstract

The harvesting of the puerulus of rock, or spiny, lobsters for seed for aquaculture is a large industry throughout the Indo-Pacific region, and an increasing number of puerulus collectors are deployed. Little is known about the ‘crowding effect’ of the collectors and how catch might be influenced by their placement relative to each other owing to a lack of aggregate statistics for puerulus collectors in this region. The rock lobsters puerulus is also collected for fisheries research, as an index of puerulus catches on collectors can provide an indicator of recruitment strength. Both as a management tool and for commercial purposes, the collectors should act independently, not reducing or influencing catch rates on adjacent or other collectors in the area. We explored the independence of collectors of the puerulus of the southern rock lobster (Jasus edwardsii (Hutton, 1875)) using a long-term-data series from four sites on the east coast of Tasmania, Australia. Arrays of collectors were in grid and cross-shaped configurations, with individual collectors spaced three metres apart. Patterns in catches were examined using generalised least squares (GLS) modelling to determine if collectors filter pueruli as they swim shoreward, testing directional, neighbour, edge, and radial effects. The results revealed that there were no significant differences in puerulus settlement among collectors at this scale of spacing, meaning that arrays with collectors even as close as 3 m apart did not interfere with each other. This finding also suggests that collectors at this spacing only capture a small proportion of the available pueruli, allowing a significant number to pass through collector grids, with no significant reduction in catch of collectors further inshore. Such a result implies that it cannot be assumed that recruitment to a natural reef will be reduced by harvesting of pueruli with this type of collector and configuration.