Abstract Bycatch in pelagic longline fleets remains a considerable source of mortality for threatened seabirds. Despite efforts to implement mitigation measures, the effectiveness of their application across multiple fleets and wide spatio-temporal scales remains poorly understood. We analyse about 15,800 sets and 36.4 million hooks observed during 583 trips aboard 132 vessels from five pelagic longline fleets (Brazil, Portugal, South Africa, Uruguay and foreign charter-vessels) operating in the south Atlantic and southwestern Indian Oceans (2002–2016) to assess the large-scale effect on bycatch rates of the implementation over time of night-setting and Tori (bird-scaring or streamer) lines. There was a highly significant decrease in standardised bycatch rate from 2002 to 2008 to 2009–2011 and a further reduction in 2012–2016, as consequence of an increased use of mitigation measures. This reduction on fleet-wide bycatch rates temporally coincides with the progressive implementation of mitigation measures in the two relevant Regional Fishery Management Organisations. Night-setting significantly reduced bycatch rates under all conditions, particularly for albatrosses. Surprisingly, bycatch rate during daylight was higher when Tori lines were deployed. Inconsistencies in Tori line deployments, entanglements with the fishing gear and the non-use of this measure with low seabird abundance may explain this pattern. At night, relative moon illumination increased bycatch rate, especially of petrels, but Tori lines significantly reduced seabird bycatch. Our results imply that a major reduction in global bycatch of threatened seabirds could be achieved, if night setting and Tori lines are correctly applied and extensively implemented by fleets operating south of 25°S.

中文翻译：

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减少海鸟兼捕：跨多个远洋延绳钓船队的夜间设置和托里线的大规模有效性

摘要 远洋延绳钓船队的兼捕仍然是受威胁海鸟死亡的重要来源。尽管努力实施缓解措施，但其在多个车队和广泛的时空尺度上应用的有效性仍然知之甚少。我们分析了在南大西洋和印度洋西南部运营的五个远洋延绳钓船队（巴西、葡萄牙、南非、乌拉圭和外国包船）的 132 艘船的 583 次航行中观察到的约 15,800 套和 3640 万条鱼钩（2002-2016 年）评估随着时间的推移实施夜间和托里（鸟类惊吓或飘带）线对兼捕率的大规模影响。从 2002 年到 2008 年到 2009-2011 年标准化兼捕率显着下降，2012-2016 年进一步下降，由于更多地使用缓解措施。船队范围内兼捕率的降低在时间上与两个相关区域渔业管理组织逐步实施缓解措施相吻合。在所有条件下，夜间设置都显着降低了兼捕率，特别是对于信天翁。令人惊讶的是，当部署 Tori 线时，白天的误捕率更高。托里线部署的不一致、与渔具的纠缠以及在海鸟丰度低的情况下未使用该措施可能解释了这种模式。夜间，相对月光照度增加了误捕率，尤其是海燕，但托里线显着降低了海鸟的误捕率。我们的结果意味着可以大幅减少全球对受威胁海鸟的兼捕，