ABSTRACT: Natural mortality, M, is a key parameter for the assessment and management of living resources but is difficult to observe directly. Therefore, M is often estimated indirectly from life history traits, and it is typically assumed to be invariant over size, age, and time. Such indirect estimators are particularly relevant for data-poor species, including many elasmobranchs (sharks, skates, and rays). However, as commonly used estimators were developed largely with teleost (bony fish) data, their performance for elasmobranchs is currently unknown. Here, we show that the relationship between observed maximum age, t_max, and mean adult M is not significantly different between teleosts (n = 105) and elasmobranchs (n = 15). Furthermore, data on 16 teleosts and 2 elasmobranchs suggest that juvenile M can be estimated from adult M when juvenile M is inversely proportional to body length and when a reference length can be provided. We introduce this reference length as the length at the age after which M is assumed to be constant and demonstrate how it can be estimated using the von Bertalanffy growth function and the proportion surviving to t_max, which is shown to be approximately 1-2%. The data utilized here also suggest that if t_max is unknown it can be estimated from growth information by assuming that 99% of the asymptotic maximum length is reached at t_max. Based on these life history parameters, the same indirect M estimators can be utilized for teleosts and elasmobranchs, which may contribute to more reliable assessments of data-poor species.

中文翻译：

---

硬骨鱼和硬骨鱼的统一自然死亡率估计

摘要：自然死亡率M是评估和管理生物资源的关键参数，但难以直接观察。因此，M通常是根据生活史特征间接估计的，并且通常假设它在大小、年龄和时间上是不变的。这种间接估计量与数据贫乏的物种特别相关，包括许多弹鳃类动物（鲨鱼、鳐鱼和鳐鱼）。然而，由于常用的估计器主要是根据硬骨鱼（硬骨鱼）数据开发的，因此它们对 elasmobranch 的性能目前未知。在这里，我们展示了观察到的最大年龄、t _max和平均成年M之间的关系硬骨鱼 (n = 105) 和 elasmobranchs (n = 15) 之间没有显着差异。此外，在硬骨鱼16和2个软骨鱼类的数据表明，少年中号可以从成人估计中号时少年中号成反比体长度，并且当可被提供的参考长度。我们引入这个参考长度作为M被假定为常数之后的年龄长度，并演示如何使用 von Bertalanffy 增长函数和存活到t _max的比例来估计它，显示大约为 1-2% . 这里使用的数据还表明，如果t _max未知 可以通过假设在t _max处达到渐近最大长度的 99% 来根据增长信息进行估计。基于这些生活史参数，相同的间接M估计量可用于硬骨鱼和 elasmobranch，这可能有助于对缺乏数据的物种进行更可靠的评估。