From Dusk Til Dawn: Modeling influences on the behavior of western rock lobster, Panulirus cygnus George

Sustainable fisheries management requires comprehensive understanding of the environmental and biological factors that drive population trends in target species. In the West Coast Rock Lobster Managed Fishery (WCRLMF), this is largely achieved through the integration of catch and catch-rate data to calculate the catchability and infer the health of the stock. However, trends in catchability may not always reflect the underlying behavior of western rock lobster. This pilot study aimed to investigate the environmental and biological influences on the behavior of western rock lobster using multi-day in-situ autonomous camera systems. We filmed three western rock lobster dens for 35 days and the abundance of rock lobsters in each den were counted hourly. We used full-subset generalized additive mixed models (GAMMs) to investigate which covariates were related to the den abundance and the proportion of lobsters present as a function of their activity. We assumed that the lobsters were more active when located outside the den. We found that western rock lobsters were more active when lunar illumination was lowest, swell was highest and when predators were present in the den. Our findings suggested that western rock lobsters may vary their hourly and daily activity in response to the relative risk of predation by foraging more when visibility was lowest and exiting or avoiding the den when a predator was present. Future studies investigating the biotic and abiotic influences on western rock lobster behavior should be undertaken in a fisheries closure to remove the possible confounding effects of fishing activity.