The Southern Flounder is a marine flatfish occurring throughout neritic zones of the northwest Atlantic and is the target of important commercial and recreational fisheries throughout its range. Recent work in the Gulf of Mexico demonstrated that the timing of hatch in this species may impact the survival of larvae, with increased survival in individuals that hatch early, ostensibly exposing them to cooler temperatures in early development in warmer years. However, hatch timing is influenced by the timing of spawning, which itself is associated with adult offshore migrations that are driven by fall and winter cold fronts. We assessed whether increasing fall temperatures in estuarine systems where Southern Flounder reside might be impacting the timing of spawning migrations. We used a machine learning approach to elicit the impact of temperature and other factors on estuarine catch in fishery-independent samples during the spawning season. Key findings of this work were as follows: (1) mean fall water temperatures in estuaries of the northwestern Gulf of Mexico have risen steadily since 1980 in accordance with broader oceanic trends, and (2) annual Southern Flounder migratory activity has shifted towards later Julian calendar dates. Temperature was an important seasonal environmental cue and is likely a key driver of spawning migrations, confirming findings from previous studies. A later shift in spawning phenology is at odds with the timing of the “survival window” for larval Southern Flounder, and this uncoupling of ideal spawning versus hatch timing could be a contributing factor to observed population declines across the range of the species.

南方比目鱼是一种分布在西北大西洋浅海区的海洋比目鱼，是其整个范围内重要的商业和休闲渔业的目标。最近在墨西哥湾的研究表明，该物种的孵化时间可能会影响幼虫的生存，早期孵化的个体的存活率会增加，表面上在温暖的年份中，它们在早期发育过程中会暴露在较低的温度下。然而，孵化时间受到产卵时间的影响，产卵时间本身与秋季和冬季冷锋驱动的成虫离岸迁徙有关。我们评估了南方比目鱼居住的河口系统秋季气温升高是否可能影响产卵迁徙的时间。我们使用机器学习方法来得出产卵季节温度和其他因素对与渔业无关的样本中河口渔获量的影响。这项工作的主要发现如下：(1) 自 1980 年以来，墨西哥湾西北部河口的平均秋季水温根据更广泛的海洋趋势稳步上升，(2) 每年的南方比目鱼迁徙活动已转向朱利安后期日历日期。温度是一个重要的季节性环境因素，也可能是产卵迁徙的关键驱动因素，这证实了之前研究的结果。产卵物候的后期变化与南方比目鱼幼体的“生存窗口”时间不一致，这种理想产卵时间与孵化时间的脱钩可能是观察到的整个物种范围内种群数量下降的一个因素。