At-sea experiment to develop the mitigation measures of seabirds for small longline vessels in the western North Pacific

For consideration to develop appropriate mitigation measures for small longline vessels, the effectiveness of 2 designs of tori-lines (A: tori-line without streamer, B: bundled 3 polypropylene bands) and (C) without tori-line was examined using chartered commercial longline vessel (Hanei-Maru No. 188, 19 GRT) in the western North Pacific by the on-board research. In the experiment, attacking rates of seabirds on baited hooks and their by-catch rates were recorded. Through 141 observations, streaked shearwaters, Laysan and black-footed albatrosses were mainly followed the vessel and all those were taking attack on baited hooks during line setting. Attacking rate by those three species (frequency of attacks/ 1000 hooks) in each segment of tori-line A, B and C was 9.5, 15.0 and 70.5, respectively. Number of by-caught birds in each segment of tori-line A, B and C was 1, 2 and 9 birds, respectively. These results indicated that all tori-lines deployed in this experiment substantially reduced bait attack and by-catch. Trial implementation of a light streamer tori-line showed entanglement of fishing gear during line setting. Further improvement and evaluation of tori-lines for small vessels should be necessary.