Institut de Recerca de la Biodiversitat (IRBio), Departament de Biologia Evolutiva, Ecologia i Ciències Ambientals, Universitat de Barcelona, Av. Diagonal 643, 08028 Barcelona, Spain.
Centre for Ecology and Conservation, College of Life and Environmental Sciences, University of Exeter, Cornwall Campus TR10 9EZ, UK.
Sci Rep. 2016 Nov 23;6:37373. doi: 10.1038/srep37373.
Fisheries provide an abundant and predictable food source for many pelagic seabirds through discards, but also pose a major threat to them through bycatch, threatening their populations worldwide. The reform of the European Common Fisheries Policy (CFP), which intends to ban discards through the landing obligation of all catches, may force seabirds to seek alternative food sources, such as baited hooks from longlines, increasing bycatch rates. To test this hypothesis we performed a combined analysis of seabird-fishery interactions using as a model Scopoli's shearwaters Calonectris diomedea in the Mediterranean. Tracking data showed that the probability of shearwaters attending longliners increased exponentially with a decreasing density of trawlers. On-board observations and mortality events corroborated this result: the probability of birds attending longliners increased 4% per each trawler leaving the longliner proximity and bird mortality increased tenfold when trawlers were not operating. Therefore, the implementation of the landing obligation in EU waters will likely cause a substantial increase in bycatch rates in longliners, at least in the short-term, due to birds switching from trawlers to longliners. Thus the implementation of the landing obligation must be carefully monitored and counterbalanced with an urgent implementation of bycatch mitigation measures in the longline fleet.
渔业通过抛弃物为许多远洋海鸟提供了丰富且可预测的食物来源，但也通过兼捕对它们构成了重大威胁，威胁着它们在全球的数量。旨在通过所有渔获物的上岸义务禁止抛弃物的欧盟共同渔业政策（CFP）改革，可能迫使海鸟寻找其他食物来源，例如延绳钓上的诱饵，从而增加兼捕率。为了验证这一假设，我们使用地中海的灰鹱（Calonectris diomedea）作为模型，对海鸟与渔业之间的相互作用进行了综合分析。跟踪数据表明，随着拖网渔船密度的降低，灰鹱在延绳钓船附近出现的概率呈指数级增长。船上观察和死亡事件证实了这一结果：每有一艘拖网渔船离开延绳钓船附近，鸟类在延绳钓船上的出现概率就会增加 4%，而当拖网渔船不作业时，鸟类的死亡率会增加十倍。因此，由于鸟类从拖网渔船转向延绳钓船，在欧盟水域实施上岸义务可能会导致延绳钓船的兼捕率大幅上升，至少在短期内会如此。因此，必须仔细监测上岸义务的实施情况，并通过在延绳钓船队中紧急实施兼捕缓解措施来加以平衡。
