Estuaries are primary habitats that serve as feeding and nursery grounds for most juvenile marine fish. However, estuaries have been used as fishing grounds by the artisanal fishers in Tanzania. The slow-growing predatory fish at juvenile and sub-adult stages are among the most frequently caught species that functionally enhance multiple linkages of energy pathways within the food web. Stomach contents and stable isotopes (δ13C and δ15N) were used to describe the nutritional sources and trophic niches between the co-existing benthic, predatory species, Carangoides chrysophrys and Epinephelus malabaricus in the Pangani estuary, Tanzania. The findings indicated significant inter-specific variations in dietary composition (PERMANOVA, p = 0.001, pseudo-F = 15.81). The prey-specific index of relative importance (%PSIRI) indicated that juvenile shrimps (%PSIRI = 51.4) and Teleostei (%PSIRI = 26.5) were the main diets of C. chrysophrys while brachyura (%PSIRI = 38.8), juvenile shrimps (%PSIRI = 25.6) and Teleostei (%PSIRI = 23.3) were important diets of E. malabaricus. The isotope mixing models indicated that the predatory fish species accumulate nutrients derived from similar autotrophic sources, microphytobenthos, seagrass and macro-algae via consumption of small fish, including clupeids and mugilids. Yet, they significantly showed different isotopic niche width with varying degree of niche overlap across the longitudinal estuary gradient. This situation was justified by the presence of basal food sources among the estuarine zones that isotopically were different. The reliance of both predators on clupeids and mugilid preys that are trophically linked with estuarine and marine basal food sources, is an indication of low estuarine food webs’ connectivity to the fresh water related food web. This situation is most likely threatening the stability of the estuarine food web structure. Management strategies and plans in place should be cautiously implemented to ensure the balanced anthropogenic freshwater use in the catchment and fishing activities, for the maintenance of the Pangani estuarine ecosystem health.

中文翻译：

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坦桑尼亚三个邦加尼河口地区两种捕食性幼鱼的营养资源和生态位差异：胃内容物和稳定同位素方法

河口是主要的栖息地，可作为大多数少年海鱼的觅食和育苗场。但是，坦桑尼亚的手工渔民已将河口用作渔场。幼年和亚成年期生长缓慢的掠食性鱼类是最常捕捞的物种之一，它们在功能上增强了食物网内能量途径的多重联系。坦桑尼亚潘加尼河口的胃底含量和稳定同位素（δ13C和δ15N）被用来描述底栖，掠食性共生食蟹类，食蟹类和斑节对虾之间并存的营养来源和营养位。研究结果表明饮食组成之间存在明显的种间差异（PERMANOVA，p = 0.001，假F = 15.81）。捕食者的相对重要性指数（％PSIRI）表明，幼虾（％PSIRI = 51.4）和Teleostei（％PSIRI = 26.5）是小C虫的主要食物，而短臂梭鱼（％PSIRI = 38.8），幼虾（ ％PSIRI = 25.6）和Teleostei（％PSIRI = 23.3）是马拉巴肠球菌的重要饮食。同位素混合模型表明，掠食性鱼类通过食用小型鱼类（包括鳞甲类和丘比特类）而积累了来自类似自养来源，微底栖动物，海草和大型藻类的营养。然而，它们显着显示出不同的同位素生态位宽度，在整个纵向河口梯度上生态位重叠程度不同。在同位素区域不同的河口区域中存在基础食物源，证明了这种情况的合理性。这两种捕食者都依赖与河口和海洋基础食物源营养相连的丘比和丘比特猎物，这表明低河口食物网与淡水相关食物网的连通性。这种情况最有可能威胁到河口食物网结构的稳定性。应谨慎执行管理策略和计划，以确保流域和捕鱼活动中人为利用淡水的平衡，以维持Pangani河口生态系统健康。