Demersal longlines with integrated weight: a preliminary assessment of sink rates, fish catch success and operational effects

Conservation Measure # 216 requires vessels fishing in sub area 88.1 + sink longlines at 0.3 m/s to 15 m depth. Sink rates can be achieved by adding external weights to lines or by using lines with weigh integrated into the rope fibres. The sink rates to 15 m depth of 9 mm demersal longlines with integrated weight (IW) were tested against unweighted longlines and lines with externally attached weights (6 kg/49 m) in the New Zealand ling fishery. Longlines with 0 g/m (unweighted), 25 g/m, 50 g/m 75 g/m and 100 g/m integrated weight averaged 0.11 m/s, 0.227 m/s, 0.272 m/s, 0.317 m/s and 0.353 m/s, respectively. The longline with externally attached weights sank at 0.32 m/s. IW longlines sank instantly, reaching 1 m depth in 6-9 s whereas unweighted lines took >20 s to reach this depth. Catch rates of ling varied with line weight but results are indeterminant due to the small sample sizes. No operational effects of using IW lines were evident during the trial. IW longlines containing 50 g/m added weight are recommended for testing in a subsequent trial to examine the effectiveness of IW longlines in reducing seabird mortality in autoline longline fisheries.