A preliminary analysis of longline fishing activity related to the bathymetry around South Georgia

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The Patagonian toothfish (Dissostichus eleginoides) is a large, predatory, nototheniid fish that is found around sub-antarctic islands and seamounts and in the cold temperate waters off Patagonia. Adult fish are usually found living close to the seabed at depths of 500 to 2,000 m whilst younger fish inhabit shallower waters. The fish, which can attain lengths in excess of 2 metres and weigh over 70 kg, are slow growing, taking between 6-10 years to reach sexual maturity and may live for more than 50 years. A longline fishery for toothfish has operated around the island of South Georgia since the early 1990’s. Between 10 and 18 vessels are licensed to fish within the South Georgia maritime zone each year. Longlines of baited hooks are usually set in water depths of 1,000 m around the South Georgia shelf edge. However, fishing effort around the island is not uniform, as fishers have established which areas are the most productive. The available charts of the region are very incomplete and only give a poor idea of the form of the continental margin. In the past this made it difficult to establish any link between fishing success and the nature of the seafloor. Recent swath bathymetry surveys, however, now reveal the detailed bathymetry of the slope and allow us to relate the areas of greatest fishing activity to the nature of the seabed. Statistical models are developed to explore whether the new bathymetry data can improve the current level of understanding on biological and fisheries characteristics of toothfish around South Georgia. This provides a preliminary insight into preferred toothfish habitats, and the potential impact of the fishery on the ecosystem. Combined, this information will influence future strategies for fishery management and conservation