Decadal trends in the South Georgia demersal fish assemblage

Data on demersal fish species composition and abundance was collected from 1277 research hauls conducted in depths < 350m during 19 research random stratified trawl surveys carried out on the Shag Rocks and South Georgia Shelf region between 1986 and 2013. Consistent hotspots of fish biomass were seen across survey years. Species counts were highly variable across the shelf region and appeared to be linked to habitat type. Low diversity in species was seen consistently over the Shag Rocks shelf. There was no detectable change in species composition across the region over three decades. Eight species from two families, the Notoheniidae and the Channichthyidae dominated the survey biomass in all years accounting for 97% of total demersal fish biomass. The relative abundance of these species was observed to change over time and between area strata. Considerable inter-annual variability in total demersal fish catch rates was observed with the highest mean CPUE s seen in surveys since 2010 but this was not uniform between strata. Trends in SSB for the five most abundant species of the South Georgia shelf show no consistent trends between species. There is evidence of increasing biomass in the marbled rock cod (N. rossii) and Mackerel icefish (C. gunnari), an overall decrease in the abundance of the Scotia Sea Icefish (C. aceratus) fluctuating but consistent biomass of the South Georgia icefish (P. georgianus) and a crash followed by a steady recovery of the Humphead notothen (G. gibberifrons). The preliminary results are considered in the context of considerable regional ecological change and a massive reduction in fishing mortality over the survey time period.