ABSTRACT: Fisheries have impacted seabird populations worldwide, either via bycatch mortality or resource depletion. Understanding the overlap between seabird distributions and fisheries is an important element for bycatch risk assessment, though the drivers of variation in seabird-fishery overlap are not well understood for some seabird populations. Here, we quantified the spatial overlap between foraging Cory’s shearwaters Calonectris borealis during the breeding season and commercial fisheries operating within the Portuguese Exclusive Economic Zone. In addition, we evaluated whether overlap varied as a function of an individual’s boldness, sex or breeding stage. For this, we GPS tracked 361 foraging trips by 72 Cory's shearwaters nesting at Berlenga Island, Portugal, over 5 consecutive breeding seasons (2012-2016). Simultaneously, we used fishing effort data from Global Fishing Watch detailing the distribution of industrial fisheries within the temporal and spatial range of Cory's shearwater tracks. Although fishing vessels were present during 88.1% of foraging trips, Cory's shearwaters spent only on average 13.3% of the time foraging in the same areas as fisheries. Such low spatial overlap is likely driven by high prey availability near the colony and suggests low direct competition for resources. We also found variation in overlap with fisheries across the breeding period, with Cory's shearwaters spending approximately 11% more time foraging in the same areas as fixed gear and purse seine vessels during pre-laying than during chick-rearing. Surprisingly, no sex or boldness-related differences were found in the overlap with any fishing gear. Our findings have implications for understanding within population variation in the overlap between fisheries and seabirds and, in turn, bycatch risk.

中文翻译：

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繁殖季节觅食的剪水与葡萄牙西海岸的工业化渔业之间的空间重叠低

摘要：渔业通过兼捕物死亡率或资源枯竭影响了全世界的海鸟种群。了解海鸟分布与渔业之间的重叠是兼捕风险评估的重要要素，尽管某些海鸟种群对海鸟与渔业重叠变化的驱动因素还不甚了解。在这里，我们量化了觅食Cory的切水Calonectrisborealis之间的空间重叠在繁殖季节和葡萄牙专属经济区内的商业捕鱼活动。此外，我们评估了重叠是否随个体的勇气，性别或繁殖阶段而变化。为此，我们连续5个繁殖季节（2012-2016年）在葡萄牙Berlenga岛上追踪了72条Cory的剪水筑巢的361次觅食行程。同时，我们使用了Global Fishing Watch的捕捞努力数据，详细介绍了Cory shear水径迹的时空范围内工业化渔业的分布。尽管在觅食旅行的88.1％期间有渔船，但Cory的剪枝水平均仅花费13.3％的时间在与渔业相同的地区觅食。如此低的空间重叠很可能是由于殖民地附近的高猎物可利用性造成的，并表明对资源的直接竞争较低。我们还发现，在整个繁殖期间，与渔业的重叠程度各不相同，科里的shear水在预产期间与固定渔具和围网渔船在相同区域的觅食时间相比，在雏鸟饲养期间花费了大约11％以上的时间。令人惊讶的是，在与任何渔具的重叠中都没有发现与性别或大胆相关的差异。我们的发现对于理解渔业和海鸟之间的重叠以及反过来兼捕的风险对种群变异的理解具有启示意义。与在鸡群饲养期间相比，在预产期与固定渔具和围网渔船在相同区域觅食的剪切水花费的时间大约多11％。令人惊讶的是，在与任何渔具的重叠中都没有发现与性别或大胆相关的差异。我们的发现对于理解渔业和海鸟之间的重叠以及反过来兼捕的风险对种群变异的理解具有启示意义。与在鸡群饲养期间相比，在预产期与固定渔具和围网渔船在相同区域觅食的剪切水花费的时间大约多11％。令人惊讶的是，在与任何渔具的重叠中都没有发现与性别或大胆相关的差异。我们的发现对于理解渔业和海鸟之间的重叠以及反过来兼捕的风险对种群变异的理解具有启示意义。