Updates on at-Sea trials into different line-weighting options for Korean Tuna Longline Vessels

Kim Y, Kim ZG, Lee SI, et al (2015) Updates on at-Sea trials into different line-weighting options for Korean Tuna Longline Vessels. IOTC, Bali, Indonesia

Introduction: The Korean tuna longline fleet catches bigeye (Thunnus obesus), yellowfin (T. albacores), albacore (T. alalunga) and southern bluefin (T. maccoyii, hereafter SBT) tunas in the southern Indian Ocean south of 25°S, where there is an overlap with several vulnerable seabird species. Since 2013, the longline industries and National Institute of Fisheries Science (NIFS) in the Republic of Korea have investigated effectiveness of seabird bycatch mitigation measures in collaboration with BirdLife International. Data collected from at-sea trials in 2013 could not be statistically analysed due to small sample size, it was surmised that 45 g Lumo leads at placed at 5 cm from the hook could be incorporated into Korean fishing operations safely (Tamini et al. 2013). The positive results encouraged NIFS to conduct additional experiments subsequently. The primary objective of the research was to explore options for adding weight to branchlines, ultimately to reduce seabird bycatch, with key indicators of success being that
1. they could be incorporated into production fishing in a manner that was safe (for crew) and operationally efficient,
2. the impact of weighting regimes on target catch rates be neutral or positive, and
3. catch rates on seabirds and other non-target species be reduced
Four additional experimental tests have been conducted to date onboard Korean vessels with two colours (luminescent and black), two weights (45 g and 60 g) added to branchlines at distances ranging from 5 cm-3 m. Two of these were completed in September and October 2015, so analysis of combined results is not possible. Preliminary indications are mixed but are generally positive, with no safety incidents recorded, and some weighting regimes catching tunas at the same rate as unweighted lines.