Bioregionalization of the South Sandwich Islands through community analysis of bathyal fish and invertebrate assemblages using fishery-derived data

The South Sandwich Islands (SSI) are a volcanic archipelago in the Atlantic sector of the Southern Ocean; they are a biologically rich area, home to a range of benthic habitats such as hydrothermal vents and seamounts. A commercial longline fishery for two congeneric species of deep-sea fish, the Patagonian (Dissostichus eleginoides) and Antarctic (D. mawsoni) toothfish has been in operation annually at the SSI since 2005 and throughout its history has employed scientific observers to collect detailed information on the species caught during fishing operations. Previous studies have investigated the distributions and communities of benthic invertebrates, sampled via scientific cruises. Here we highlight the utility of demersal longlines as spatially extensive sampling tools to investigate both invertebrate and fish communities at the SSI. A clear gradient in the distribution of many fish and invertebrate species is evident across the latitudinal range of the archipelago and many of the sampled fish species also have statistically significant relationships with depth. These distributions result in clear differences in fish communities between the north, mid, and south of the islands, whilst the invertebrate communities are less clearly delineated. Environmental variables were investigated as drivers in these communities, and seawater temperature appears to be a key abiotic factor in mediating the distributions of species and communities. As many of these communities are structured based on temperature dependent species distributions, it is likely climate change will alter these communities with poleward shifts in the ranges of many species.