This document seeks the approval of CCAMLR for a research plan to improve the seabird by-catch mitigation effectiveness of the Spanish system of longline fishing. The plan also aims to reduce the amount of fishing gear (and ghost fishing) lost in benthic habitats by Spanish system vessels in the Convention area and, potentially, in other fisheries where Spanish system vessels operate. A step-wise approach will be taken using a chartered fishing vessel in Chile to trial various line weighting systems, including replacing with steel sinker weights the bags of rocks that are traditionally used by Spanish system vessels. The objectives are to (a) reduce the degree of lofting in hook lines between line weights that occurs with the CCAMLR line weighting regime to expedite sink rates in surface waters, and (b) reduce the incidence of line weight hook-ups on the seabed. A line weighting system that improves sink profiles (and reduces frequency of line breakage) will then be trialled in normal fishing operations in southern Chile to determine effectiveness (along with use of streamer lines) as deterrent to black-browed albatrosses. The operational effectiveness of the new regime will also be determined. Assuming the new regime is practical to use, the intention will then be to seek permission from CCAMLR to trial the improved mitigation measures against white-chinned petrels in sub Area 48.3 at a high risk time of year.