Bycatch in the Antarctic krill (Euphausia superba Dana, 1850) pelagic trawl fishery by subarea and day/night

The presence of bycatch in Antarctic krill (Euphasia superba) fishing operations in statistical subareas 48.1 and 48.2 was determined on board the Antarctic Endeavour factory ship in 10 fishing trips made between 2017-2018 and 2020-2021 seasons. In each haul, organisms other than the target species were removed from the conveyor belt, identified by species, and weighed, which were later grouped and labeled into Pisces and Other taxa. A total of 2069 fishing hauls
were analyzed, with a total bycatch capture of 2320.58 kg, registering organisms other than krill in 1073 hauls (52.2%). The bycatch estimates by season, subarea, and according to whether they were carried out during light (day) or darkness
hours (night) were carried out using two indices: catch rate (CR), which corresponds to the relationship between the weight of these organisms and the total weight of krill caught, and the catch per hour towed (CPUE). In the four seasons
analyzed, it was determined that the number of species identified in the bycatch increased from 14 to 25. The fish with the highest average frequency of occurrence (>5%) corresponded to Chionodraco rastrospinososus (9.98-26.97%), Champsocephalus gunnari (8.54-12.08%), Pseudochaenichthys georgianus (6.59-9.55%), Chaenocephalus aceratus (1.23-15.58%), Neopagetopsis ionah (2.74-14.00%), Gobionotothen gibberifrons (0.82-9.21%), and Pleurogramma antarcticum (0.48-10.55%). In Other taxa, Salpidae (0.84-25.09%) and Amphipoda (0.50-18.68%) stand out. Additionally, globally, high variability was established in the bycatch indices between the seasons; however, notably higher values of CR and CPUE were determined in Subarea 48.1 and during the day, compared to those established in the other subarea and at night .