Following Operation Sparrow 2, WG-FSA-17 noted the unprecedented availability of catch data from four IUU vessels including reported removals, video footage, and catch in gillnets recovered by an NGO vessel. As requested in WG-FSA-17 paragraph 2.16, this document provides an analysis of the spatio-temporal distributions of catch and effort by the Chang Bai, Nihewan and Jiangfeng in Division 58.4.1 during the 2013/14 season, as well as the Thunder in Division 58.4.3b during the 2014/15 season. During the 2013/14 season the Chang Bai, Nihewan and Jiangfeng operated across SSRUs 58.4.1C, 58.4.1D and 58.4.1E and caught a total of 792 tonnes of toothfish. Daily catch rates were similar between IUU and authorised vessels. Based on data from 2013/14, total removals by IUU vessels fishing with gillnets were higher than authorised vessels fishing with longlines, and the presence of an authorised vessel in the region of IUU activity did not appear to deter the IUU fleet. Hence there have been substantial and unaccounted for IUU removals, which may have impacted on research activities in Division 58.4.1.