DISTRIBUTION AND ABUNDANCE OF ANTARCTIC TOOTHFISH IN THE ROSS SEA

This report is a synthesis of mostly existing information which has been compiled for the purposes of addressing items on the FEMA 2 agenda. It summarises the management of the fishery, catch and effort, size distribution, and tagging data collected from the Antarctic toothfish fishery up to the 2007/08 fishing year. It focuses in particular on Antarctic toothfish catches taken from the continental shelf of the Ross Sea itself, because this is the area where any ecosystem effects related to predators of toothfish are most likely to occur. Of the total catch from the fishery to date of almost 19 000 t, about 20% has been taken from the northern grounds, 70% from the continental slope, and 10% from the continental shelf of the Ross Sea. The shelf catch has been taken from three quite localised fishing grounds of deep water (mainly > 800 m) off Terra Nova Bay, Ross Island, and in the south of 88.1L (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. There are no reliable estimates of Antarctic toothfish abundance on the shelf at the current time. In preparing this paper we have identified some data sources which could potentially be used to estimate the abundance of toothfish on the Ross Sea shelf. However, CPUE is inherently variable both within and between seasons on the various fishing grounds and different vessels have fished different grounds in different years making interpretation difficult. Tag-recapture data from the Terra Nova Bay fishing ground would also be difficult to interpret because of the movement of tagged fish. There is also other information on the distribution of Antarctic toothfish from the area derived from other research surveys and from studies focusing on other species. US Scientists at McMurdo Sound have collected Antarctic toothfish since 1971 using vertical set lines. Their sampling has shown significant within and between season variability in catch rates. Very few Antarctic toothfish have been caught in the Ross Sea by other research sampling. Indirect observations from cameras mounted on seals shows that Antarctic toothfish at McMurdo Sound can occupy the entire water column, but the spatial and temporal extent of its midwater distribution and the proportion of the population which occurs off the bottom are unknown.