The environmental influence on the long-term variations of fish population structure, mainly that which drives the movements between segregated life stages, is not yet fully understood in estuarine systems. As a case study, we used seasonal (winter, spring) fishery-independent data of whitemouth croaker (Micropogonias furnieri) to determine the influence of environmental drivers (salinity, temperature, depth, freshwater outflow, and wind) on the long-term inter-annual scale (1993–2006) variation in the population structure. We used an approach based on size assemblages to represent and model the length distribution of the population structure. The different size assemblages (four in winter, five in spring) identified and verified by ordination analyses (cluster and nMDS) indicated a demographic structure that resembled juveniles, adolescent, and adult stages. The size assemblage composition showed significant inter-annual differences in both seasons. Additionally, there was significant decrease in the abundance of most size assemblages, except for juveniles which increased in winter. A multivariate regression tree analysis indicated that salinity expressed a greater influence on the size assemblage composition than the temperature. Moreover, the river outflow showed greater localized effects at the upper estuary across the variation in the spatial cover of salinity, which favored juveniles. On short time scales (between consecutive years), demographic variations responded to changes in the availability of environmental conditions preferred by each size assemblage, whereas long-term variations could be attributed to other effects (e.g. fishing mortality, habitat degradation).

河口系统尚未完全了解环境对鱼类种群结构长期变化的影响，主要是驱动分离生命阶段之间运动的环境影响。作为案例研究，我们使用了与季节性（冬季，春季）无关的白嘴鱼（Micropogonias furnieri）数据）以确定环境驱动因素（盐度，温度，深度，淡水流出和风）对人口结构的长期年际尺度（1993-2006）变化的影响。我们使用了一种基于规模组合的方法来表示和建模人口结构的长度分布。通过协调分析（集群和nMDS）确定并验证的不同大小的组合（冬季四个，春季五个）表明，其人口结构类似于少年，青少年和成年阶段。尺码组合的组成在两个季节中均显示出明显的年际差异。另外，除了冬天增加的幼鱼外，大多数大小的鱼群的数量也显着减少。多元回归树分析表明，盐度对尺寸组合物的影响大于温度。此外，在盐度空间覆盖变化的情况下，河口在较高的河口处表现出更大的局部影响，这有利于幼鱼。在较短的时间尺度上（连续几年之间），人口变化对每种规模组合所偏好的环境条件的可用性做出了响应，而长期变化则可能归因于其他影响（例如捕鱼死亡率，栖息地退化）。