Illegal, unregulated and unreported (IUU) fishing vessels are increasingly using gillnets as a fishing method to target toothfish in the Convention area. Estimating the impact of IUU fishing is hampered by a lack of data on the design, deployment, catch and bycatch rates of gill nets. This paper describes a gillnet found abandoned by Australian vessel patrolling BANZARE Bank (Statistical Division 58.4.3b), and the toothfish and bycatch found when a section of the gillnet was retrieved. Based on the amount of toothfish found in the 8 km long section of net retrieved, upwards of 29 tonnes of intact toothfish may be removed by a single vessel’s deployment of a 130 km long series of gillnets. However these figures are likely to be underestimates of total mortality in gillnets, due to the evidence of large numbers of sea-lice depredated fish in the net.