Analysis of the by-catch of Channichthys rhinoceratus and Lepidonotothen squamifrons from the fisheries at Heard Island and the McDonald Islands (Division 58.5.2)

The unicorn icefish, Channichthys rhinoceratus and the grey rock cod, Lepidonotothen squamifrons are among the most common species bycaught in the toothfish and mackerel icefish trawl fisheries at Heard Island and McDonald Islands (HIMI) (Division 58.5.2). These species are rarely taken in the longline fishery, but form the most abundant bycatch of the trawl fisheries after skates (Bathyraja spp.). In the toothfish fishery both species are taken, whereas C. rhinoceratus is much more common in the bycatch of the mackerel icefish fishery than L. squamifrons. Over the 15 years of the fisheries, approximately 20 t of C. rhinoceratus and 9 t of L. squamifrons were caught annually. The commercial and research data analysed in this study shows that both species are widespread over the plateau in waters of <1000 m. In most areas they occur at densities <100 kg.km^-2, but each species has separate areas of aggregation where densities exceed 1 t.km^-2. The annual take of these species is well below the precautionary bycatch limits set by CCAMLR, move-on rules apply, and a substantial part of their distribution occurs within the HIMI Marine Reserve, and therefore current bycatch levels are likely to be low risk. However, we intend to conduct a study of the population dynamics of these species to further evaluate the performance of current management measures.