Harbor porpoises exhibit early maturation, relatively short gestation/lactation periods and a faster rate of reproduction as compared to other cetacean species. Intrinsic and extrinsic factors can influence both population vital rates and population structure, which ultimately cause changes in dynamics within and between populations. Here, we undertook a retrospective analysis of mortality data collected over a 24-year period for assessing life history traits of the North-east Atlantic harbor porpoise population. We use time-period specific models for key life history relationships that considered cause of death of individuals (as a proxy for health status), sex and management unit (MU). Sexual variation in asymptotic length, asymptotic age, average length at 50% maturity (L50) and average age at 50% maturity (A50) were observed, with females attaining a larger asymptotic length, larger L50, and delaying attainment of both sexual and physical maturity, compared to males. While females are constrained in their minimum body size due to giving birth to proportionally larger offspring, males exhibited more plasticity in size at sexual maturity, enabling re-allocation of available energy resources toward reproduction. Data were then used to compare biological parameters among two porpoise MUs in United Kingdom waters, both of which in the current study exhibited reduced reproductive rates compared to other geographic regions. In both MUs, females significantly increased their A50 and males significantly declined in their L50. An increase in the age at asymptotic length was also observed in both sexes, along with a significant decline in the Gompertz growth rate parameter that was more apparent in the female data. While availability of suitable prey resources may be a limiting factor, a combination of other factors cannot be ruled out. Porpoises in the Celtic and Irish Seas MU were significantly larger in their maximum length, asymptotic length and L50 compared to porpoises in the North Sea MU throughout the study period, suggesting limited gene flow between these two MUs. These results justify the maintenance of these harbor porpoise MUs or assessment units, as two separate units, within the range of the North-east Atlantic population, and for indicator assessments under the EU’s Marine Strategy Framework Directive.

中文翻译：

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东北大西洋港湾鼠海豚生活史参数的时空变异性

与其他鲸类物种相比，港湾鼠海豚成熟早，妊娠/哺乳期相对较短，繁殖速度更快。内在和外在因素都会影响人口生命率和人口结构，最终导致人口内部和人口之间的动态变化。在这里，我们对 24 年期间收集的死亡率数据进行了回顾性分析，以评估东北大西洋港湾鼠海豚种群的生活史特征。我们将特定时间段的模型用于考虑个人死亡原因（作为健康状况的代理）、性别和管理单位 (MU) 的关键生活史关系。观察到渐近长度、渐近年龄、50% 成熟时平均长度 (L50) 和 50% 成熟时平均年龄 (A50) 的性别差异，与男性相比，女性获得更大的渐近长度、更大的 L50 和延迟达到性成熟和身体成熟。虽然雌性由于生育成比例更大的后代而限制了它们的最小体型，但雄性在性成熟时表现出更大的体型可塑性，从而能够将可用的能量资源重新分配给繁殖。然后使用数据来比较英国水域中两只海豚 MU 的生物学参数，在当前的研究中，与其他地理区域相比，这两种鼠海豚的繁殖率都较低。在这两个 MU 中，女性的 A50 显着增加，而男性的 L50 显着下降。在两性中也观察到渐近长度的年龄增加，以及 Gompertz 增长率参数的显着下降，这在女性数据中更为明显。虽然合适的猎物资源的可用性可能是一个限制因素，但不能排除其他因素的组合。在整个研究期间，与北海 MU 中的江豚相比，凯尔特海和爱尔兰海 MU 中的江豚的最大长度、渐近长度和 L50 明显更大，这表明这两个 MU 之间的基因流有限。这些结果证明将这些港湾鼠海豚 MU 或评估单位作为两个独立的单位，在东北大西洋种群范围内进行维护，并根据欧盟海洋战略框架指令进行指标评估是合理的。不能排除其他因素的组合。在整个研究期间，与北海 MU 中的江豚相比，凯尔特海和爱尔兰海 MU 中的江豚的最大长度、渐近长度和 L50 明显更大，这表明这两个 MU 之间的基因流有限。这些结果证明将这些港湾鼠海豚 MU 或评估单位作为两个独立的单位，在东北大西洋种群范围内进行维护，并根据欧盟海洋战略框架指令进行指标评估是合理的。不能排除其他因素的组合。在整个研究期间，与北海 MU 中的江豚相比，凯尔特海和爱尔兰海 MU 中的江豚的最大长度、渐近长度和 L50 明显更大，这表明这两个 MU 之间的基因流有限。这些结果证明将这些港湾鼠海豚 MU 或评估单位作为两个独立的单位，在东北大西洋种群范围内进行维护，并根据欧盟海洋战略框架指令进行指标评估是合理的。