The difference in the number of white-chinned petrels (Procellaria aequinoctialis) and sooty shearwaters (Puffinus griseus) killed by unweighted longlines (UW; mean sink rate to 20 m depth: 0.11 m/s) and longlines containing 50 g lead/m integrated weight (IW; mean sink rate: 0.24 m/s) was examined in the New Zealand ling (Genypterus blacodes) autoline longline fishery. The experiments were conducted in the seabird breeding seasons (October/November) of 2002 and 2003 on F/V’s Janas and Avro Chieftain. White-chinned petrels and sooty shearwaters are more difficult to deter from baited hooks than the seabird species occurring in Divisions and Subareas where night setting exemption currently applies, and are considered a worse-case scenario from a risk assessment perspective. In the experiments the Janas and Avro Chieftain were followed by large number of seabirds, including 200-1,400 white-chinned petrels and up to 400 sooty shearwaters. Lines were set in day-light and at night, and a single streamer line was deployed on all sets. Differences between IW and UW lines in the catch rates of white-chinned petrels, sooty shearwaters and albatrosses, and ling and non-target fish species were determined for each pair of magazines or lines by counting dead birds during line hauling. In 2002 80 white-chinned petrels were caught on UW lines compared to one white-chinned petrel on IW; the reduction in mortality was 98.7% (CL95% = 99.8-90.6%; P<0.001; n = 35 pairs of magazines). One sooty shearwater was caught on UW and none on IW. In 2003 46 white-chinned petrels were caught on UW and three petrels on IW; the reduction in mortality was 93.5% (CL95% = 98.02-78.5%, P<0.001; n = 25 pairs of lines). Sooty shearwater mortality was 38 on UW lines and 15 on IW lines, a reduction of 60.5% (CL95% = 78.6-27.4%, P = 0.002; n = 25 pairs of lines). Catch rates of white-chinned petrels on IW were 0.005/’000 hooks and 0.011/’000 hooks in 2002 and 2003, respectively. Catch rate of sooty shearwaters in 2003 was 0.053/’000 hooks. No albatrosses were caught on either line type in 2002; in 2003 a single Salvin’s albatross was caught on a UW line. Catch rates of ling and non-target fish species were not affected by use of IW longlines. The use of IW longlines by autoline vessels operating in Divisions and Subareas where night setting exemption currently applies would require relaxation of the minimum line sink rate (0.3 m/s; CM 24-02) to permit the slower sink rate of IW (mean: 0.24 m/s; range 0.20-0.29 m/s). It is recommended that CM 24-02 be amended so that autoline vessels operating in high latitude Divisions and Subareas where exemption from night applies be permitted the option of using IW longlines with 50 g lead/m and an average longline sink rate of 0.24m/s.
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