Preliminary trials to test mitigation measures aimed at reducing Macrourus spp. by-catch on autoliners targeting D. eleginoides with longlines in the CCAMLR Convention Area

Pilot studies were carried out in 48.3 in 2006 and in 88.1 and 88.2 in 2007 by the Argos Helena, testing 14/0 circle hooks and mackerel bait against hooks and bait routinely used by the vessel (14/0 EZ J-type hooks and squid bait respectively). Catch per unit effort (CPUE) of Macrourus spp. (kg 1000 hooks-1) was lowest with J-type hooks and mackerel bait for both regional trials. Variation in catch rates of Macrourus spp due to bait was significant, but not for hook-type. Bait type had similar effects on the catch rates of Dissostchus spp. and of all other by-catch species combined. However, variation in CPUE for target and non-target species due to geographical location, depth and soak time were also significant and when bycatch to catch ratios were analysed, the variation due to bait was not significant. In order for the benefits of mackerel bait in reducing macrourid (and other species) bycatch to be endorsed by the industry, further mitigation research is required to determine a gear configuration for automated longlines which maintains toothfish catch rates when this bait type is being used.