Assessment of stone crab (Lithodidae) density on the South Georgia slope using baited video cameras

During January 2000 a baited video camera system was deployed fifteen times at depths of 719-1518 m around the sub-Antarctic island of South Georgia. Four species of lithodid (Anomura: Lithodidae) crab (Paralomis formosa, P. spinosissima, Lithodes sp. and Neolithodes diomedeae) were attracted to the baits of which Paralomis formosa was the most abundant. Using arrival rate at baits, predictions of odour plume size and observations of walking speed the abundance of the stone crab Paralomis formosa was estimated. Numbers of crabs increased rapidly following bait emplacement, with total numbers observed in the 4.9 m2 field of view exceeding 50 within 200 minutes on three occasions. Current speed was used to predict the area of the odour plume, and by integrating the area to account for scavenger speed the effective area of the odour plume was obtained. The density of crabs, estimated from the increase in crab numbers per unit area of odour plume, averaged 8313 individuals km-2 (range 1100-25600). Density was not significantly correlated with depth, temperature or current speed and variability was attributed to substrate form.