Beverton & Holt's (1957) functional definition of maturity in fish (L₅₀), as being the size class in which 50% of individuals begin producing gametes in some proportion to body weight, is widely used in assessment models to estimate spawning stock biomass, and manage the minimum size of capture. Standardized histological techniques for estimating L₅₀ apply physiological definitions that identify cellular or hormonal markers indicating individuals are capable of producing gametes. Few studies have examined how those phases of gonadal development correlate with reproductive behaviour or reproductive output. We compare histological estimates of L₅₀ for 10 species of reef fish from Palau, with the size composition of catches, surveys and spawning aggregations, and interpret those comparisons with simulation modelling. Our study shows that the histological L₅₀ estimates coincide with the size species begin ontogenetically shifting between juvenile and adult habitat, and with the size the smallest individuals join spawning aggregations, but are ~15% smaller than the length at which we infer 50% of individuals begin joining spawning aggregations. This highlights a mismatch between the functional definition of L₅₀ assumed for assessment and management, and the physiological definitions developed for histological studies, which identify the beginning of a sub-adult adolescent phase, rather than the end, when functional adulthood starts. This definitional mismatch could be causing stock assessments to systematically over-estimate the reproductive output of fisheries. By considering fish behaviour, we hope to better align estimates of physiological maturation with the estimation of functional reproductive potential required for assessment and management.

中文翻译：

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标准组织学技术系统地低估了鱼开始产卵的大小

Beverton & Holt (1957) 对鱼类成熟度 ( L ₅₀ ) 的功能定义，作为 50% 的个体开始产生与体重成一定比例的配子的大小等级，广泛用于评估模型以估计产卵种群生物量，并管理捕获的最小大小。用于估计L ₅₀的标准化组织学技术应用生理学定义来识别细胞或激素标志物，表明个体能够产生配子。很少有研究检查性腺发育的这些阶段如何与生殖行为或生殖输出相关联。我们比较L _{50的组织学估计}来自帕劳的 10 种珊瑚鱼，包括渔获量、调查和产卵聚集的大小组成，并通过模拟建模解释这些比较。我们的研究表明，组织学L ₅₀估计值与开始在幼体和成体栖息地之间发生个体发育变化的物种大小一致，并且最小个体的大小加入产卵聚集体，但比我们推断的 50% 的长度小约 15%个体开始加入产卵聚合。这突出了L _{50的功能定义之间的不匹配}假设用于评估和管理，以及为组织学研究制定的生理定义，这些定义确定了亚成年青少年阶段的开始，而不是功能性成年开始时的结束。这种定义不匹配可能导致种群评估系统地高估渔业的繁殖产出。通过考虑鱼类的行为，我们希望更好地将生理成熟度的估计与评估和管理所需的功能生殖潜力的估计相结合。