The incidental mortality of seabirds in fisheries remains a serious global concern. Obtaining unbiased and accurate estimates of bycatch rates is a priority for seabird bycatch mitigation and demographic research. For measuring the capture risk of seabird interactions in fisheries, the rate of carcass retrieval from hauled gear is commonly used. However, reliability can be limited by a lack of direct capture observations and the substantial pre-haul bycatch losses known to occur, meaning incidence of seabird bycatch is underestimated. To solve this problem, a new measure (bycatch vulnerability) that links an observed interaction directly to the underlying capture event is proposed to represent the capture risk of fishery interactions by seabirds. The new measure is not affected by subsequent bycatch loss. To illustrate how to estimate and analyse bycatch vulnerability, a case study based on a long-term dataset of seabird interactions and capture confirmation is provided. Bayesian modelling and hypothesis testing were conducted to identify important bycatch risk factors. Competition was found to play a central role in determining seabird bycatch vulnerability. More competitive environments were riskier for seabirds, and larger and thus more competitive species were more at risk than smaller sized and less competitive species. Species foraging behaviour also played a role. On the other hand, no additional effect of physical oceanic condition and spatio-temporal factors on bycatch vulnerability was detected. Bycatch vulnerability is recommended as a replacement for the commonly used bycatch rate or carcass retrieval rate to measure the capture risk of an interaction. Combined with a normalized contact rate, bycatch vulnerability offers an unbiased estimate of seabird bycatch rate in pelagic longline fisheries.

渔业中海鸟的偶然死亡仍然是一个严重的全球问题。获得对兼捕率的公正和准确估计是减少海鸟兼捕和人口研究的优先事项。为了衡量渔业中海鸟相互作用的捕获风险，通常使用从牵引装置中取出尸体的速率。然而，可靠性可能受到缺乏直接捕获观察和已知发生的大量运输前兼捕损失的限制，这意味着海鸟兼捕的发生率被低估了。为了解决这个问题，提出了一种将观察到的相互作用直接与潜在捕获事件联系起来的新措施（兼捕脆弱性），以表示海鸟渔业相互作用的捕获风险。新措施不受后续兼捕损失的影响。为了说明如何估计和分析兼捕脆弱性，提供了一个基于海鸟相互作用和捕获确认的长期数据集的案例研究。进行了贝叶斯建模和假设检验，以确定重要的兼捕风险因素。发现竞争在确定海鸟兼捕的脆弱性方面发挥着核心作用。更具竞争性的环境对海鸟来说风险更大，较大且因此更具竞争力的物种比体型较小且竞争力较弱的物种面临的风险更大。物种的觅食行为也起了一定作用。另一方面，没有检测到物理海洋条件和时空因素对兼捕易损性的额外影响。建议将兼捕漏洞作为常用的兼捕率或尸体回收率的替代品，以衡量交互的捕获风险。结合标准化的接触率，兼捕脆弱性提供了中上层延绳渔业中海鸟兼捕率的无偏估计。