ABSTRACT: Entanglement in fishing gear is a significant threat to many cetaceans. For the 2 largest species, the blue whale Balaenoptera musculus and the fin whale B. physalus, reports of entangled individuals are rare, leading to the assumption that entanglements are not common. Studies of interaction with fisheries in other species often rely on the presence of scars from previous entanglements. Here, scar detection rates were first examined in humpback Megaptera novaeangliae, fin and blue whales using standard vessel-based photo-identification photographs collected between 2009 and 2016 in the Gulf of St. Lawrence, Canada. We then examined aerial images of fin whales collected with a drone in 2018 and 2019 and compared both methods. Entanglement rates were 6.5% for fin and 13.1% for blue whales using photo-identification images of individuals. Prominent scarring was observed around the tail and caudal peduncle, visible only when animals lifted those body sections above water when diving. For the small subset of pictures which captured the entire caudal peduncle, entanglement rates ranged between 60% for blue and 80% for fin whales. This result was similar to the 85% entanglement rate estimated in humpback whales. The assessment of aerial-based photography yielded an entanglement rate of 44.1 to 54.7% in fin whales. Scars were always around the peduncle, often the tail, rarely the dorsal fin and never around the pectoral fins, while the mouth cannot be examined from above. Thus, in species that do not regularly expose their tail or peduncle, aerial imagery is the preferred method to quantify entanglement rates by assessment of scars.

中文翻译：

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悬而未决：无人机图像揭示了对大型不规则鲸鱼的纠缠率的低估

摘要：渔具纠缠是对许多鲸类的重大威胁。对于2个最大的物种，蓝鲸Balaenoptera musculus和大须鲸B. physalus，很少有被纠缠的个体的报告，这导致人们认为纠缠并不常见。与其他物种的渔业相互作用的研究通常依赖于先前纠缠造成的疤痕。在这里，首先在座头鲸Megaptera novaeangliae中检查了疤痕检测率，鳍和蓝鲸使用2009年至2016年之间在加拿大圣劳伦斯湾收集的基于船只的标准照片识别照片。然后，我们检查了2018年和2019年用无人机收集的长须鲸的航拍图像，并比较了这两种方法。使用个人的照片识别图像，鳍的缠结率为6.5％，蓝鲸的缠结率为13.1％。在尾巴和尾柄周围观察到明显的疤痕，只有在潜水时动物将这些身体部分举到水面以上时才能看到。对于捕获整个尾柄的小图片子来说，蓝色的纠缠率在60％到鲸鱼的纠缠率在80％之间。这个结果类似于座头鲸估计的85％纠缠率。对空中摄影的评估得出，鲸鱼的纠缠率为44.1％至54.7％。疤痕总是在花梗周围，经常是尾巴，很少在背鳍上，在胸鳍上也没有，而从上方不能检查嘴巴。因此，在不规则暴露尾巴或花梗的物种中，航空影像是通过评估疤痕来量化纠缠率的首选方法。