Distribution and relative abundance of Antarctic toothfish (Dissostichus mawsoni) on the Ross Sea shelf
This paper summarises knowledge of the distribution and relative abundance of Antarctic toothfish (Dissostichus mawsoni) on the Ross Sea shelf (defined here as the continental shelf out to the edge of the shelf break at about 600–800 m depth). The focus is on D. mawsoni catches from the shelf, as this area is likely to have the greatest overlap between D. mawsoni and potential predators, and thus where any ecosystem effects would be most likely to occur. The shelf catch has been taken mainly in depths greater than 800 m from three localised fishing grounds of deep water off Terra Nova Bay, Ross Island, and in the south of small-scale research unit (SSRU) 881L (adjacent to the Ross Ice Shelf). The catch rates from the exploratory longline fishery typically show high temporal and spatial variability, even between consecutive sets within the main fishing grounds. Most toothfish caught in the southern Ross Sea were sub-adult and maturing fish, typically ranging from 60–130 cm in length, with some evidence for an ontogenetic migration from east to west as they grow. From the fisheries data available, there is no evidence for a northward contraction in the range of D. mawsoni over the course of the fishery. Nevertheless, it would seem prudent to have a monitoring system in place so that changes in relative abundance of these subadult fish could be detected. It is recommended that CCAMLR consider developing a sub-adult longline survey to monitor this part of the population.