Methodological comparison for sampling populations of a commercially important rock lobster species

Wild populations of rock lobsters are sampled to aid in assessments of the fisheries stocks, the impact of marine reserves, as well as biological and ecological studies. The two most prevalent methods for sampling rock lobsters are pots (traps) and diver-based surveys. While many studies have individually investigated the inherent biases and uncertainties for these methods, no thorough comparison across these methods has been completed. Here, we examined four pot designs and two diver surveys methods for their ability to adequately sample the western rock lobster, Panulirus cygnus George, 1962. Methods were tested for their ability to: (1) capture sufficient individuals, (2) sample a large size-range, and (3) detect differences in relative abundance. A modified pot design, "meshed recreational," proved to be the most efficient and unbiased of all the methods examined. These pots sampled an average of 177 lobsters d(-1), captured a large range of lobster sizes (40.4-158 mm), and were capable of detecting known patterns in abundance. Abundance indices produced by the two dive-based methods were found to be less accurate in detecting the patterns of known abundance, and did not produce better size-composition data than the modified pots. It is likely that variation in habitat complexity meant the two dive methods were inefficient for sampling P. cygnus in the present study. Outcomes presented here highlight the need to carefully select methods appropriate to the particular species, its habitat, and the aims of the study being conducted.