Abstract

Sardine Sardinops sagax is an ecologically and economically important Clupeid found off the entire South African coast that includes both coastal upwelling and western boundary current systems. Although the management of the sardine fisheries historically assumed a single, panmictic population, the existence of three, semi-discrete subpopulations has recently been hypothesized. We conducted otolith δ¹⁸O and microstructure analyses to investigate nursery habitat temperatures and early life growth rates, respectively, of sardine collected from three biogeographic regions around South Africa’s coast to test that hypothesis. Analyses indicated that for both summer- and winter-captured adults and summer-captured juveniles, fishes from the west coast grew significantly slower in water that was several degrees cooler than those from the south and east coasts. This suggests that mixing of sardines between regions, particularly the west and other coasts, is relatively limited and supports the hypothesis of semi-discrete subpopulations. However, the west-south differences disappeared in the results for winter-captured juveniles, suggesting that differences in early life conditions between regions may change seasonally, and/or that all or most winter-captured juveniles originated from the west coast. Further elucidating the interactions between South African sardine subpopulations and the mechanisms thereof is important for sustainable harvesting of this species.

中文翻译：

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耳石δ18O和微观结构分析提供了南非周围沙丁鱼Sardinops sagax种群结构的进一步证据

摘要

沙丁鱼Sardinops sagax是在整个南非沿海发现的具有生态和经济意义的科鲁皮德，包括沿海上升流和西部边界洋流系统。尽管从历史上看，沙丁鱼渔业的管理假设是一个单一的大流行种群，但最近有人假设存在三个半离散的亚种群。我们耳石进行δ ¹⁸O和微观结构分析分别调查了从南非沿海三个生物地理区域收集的沙丁鱼的苗圃栖息地温度和早期生命增长率，以检验该假设。分析表明，对于夏季和冬季捕获的成年成年人以及夏季捕获的幼鱼而言，西海岸的鱼类在水中的生长速度明显慢，比南海岸和东海岸的鱼类凉爽几度。这表明沙丁鱼在区域之间，特别是在西部和其他沿海地区之间的混合相对有限，并支持了半离散亚群的假设。但是，冬季捕获的青少年的结果没有南北差异，这表明不同地区之间早期生活条件的差异可能会随季节变化，和/或所有或大多数被冬季捕获的少年都来自西海岸。进一步阐明南非沙丁鱼亚群之间的相互作用及其机制对于该物种的可持续收获很重要。