Effects of trap-shape, bait, and soak-time on sampling the eastern rock lobster, Jasus verreauxi

It is important when analysing catch and effort information from either fishery-dependent or fishery-independent sources, to understand how external factors influence catches so that data can be standardised to be more representative of the abundance of the target species. In New South Wales, Australia, commercial fishers primarily use trapping as the method to capture the eastern rock (spiny) lobster (Jasus verreauxi) and consider trap-shape, bait-type, and soak-time to be the most important factors affecting their catches. Two experiments were done to test hypotheses about the influence of these factors upon catches of lobsters on inshore,grounds (< 15 m depth). There were no differences in mean numbers caught between bait-types (flathead, redfish, or blackfish) and soak-times (1-3 days), but trap-shape (beehive, rectangular, or D-shaped) affected catches. D-shaped and rectangular traps caught more lobsters than beehive traps. There were no differences in the sizes of lobsters caught between trap-shapes and the sex ratios did not differ from unity, suggesting that there were no differences in selectivity between trap-shapes. It is recommended that the compulsory daily log sheets in place in the fishery require commercial fishers to provide information about the shape of the traps they use. When designing fishery-independent surveys to sample juvenile J. verreauxi, it is recommended that: (1) groups of rectangular traps be set as a single replicate to saturate a defined area; (2) as many replicates as practically possible be included; (3) any of the bait-types described in this paper be used; and (4) the soak-time for the gear be one day.