Table_1_Spatial and Ontogenetic Patterns in the Trophic Ecology of Juvenile Bull Sharks (Carcharhinus leucas) From the Northwest Gulf of Mexico.pdf

A combination of stomach content and stable isotope (δ13C, δ15N, and δ34S) analyses were used to characterize and examine spatiotemporal and ontogenetic trends in the feeding ecology of juvenile bull sharks (Carcharhinus leucas) captured in estuaries throughout the northwest Gulf of Mexico (GoM) between 2013 and 2016. Shark diets were dominated by fish prey taxa [>98% index of relative importance (%IRI)], and of those identified to the family level, two families comprised greater than 50% IRI, Mugilidae (mullets: ∼32%) and Sciaenidae (drums and croakers: 27%). Clupeidae (herrings: 14%) and Ariidae (sea catfishes: 15%) also contributed substantially to the diet of juvenile sharks, though consumption of Ariidae increased as consumption of Clupeidae decreased in juvenile sharks larger than 893 mm Fork Length (FL) (∼1 year old). Values of δ15N increased significantly with shark size, indicating a shift toward larger or higher trophic level prey with increasing shark size. Latitudinal and temporal trends in δ13C and δ34S suggest isotopic variation occurred in correspondence with shifts in primary producer assemblages and environmental drivers of sampled estuaries. These results highlight the importance of teleost prey resources along the freshwater-marine continuum in the diet of juvenile bull sharks, as well as the utility of natural tracers in tracking ontogenetic trends in feeding ecology.

本研究联合胃含物分析与稳定同位素（δ¹³C、δ¹⁵N、δ³⁴S）分析方法，对2013至2016年在墨西哥湾西北部（Gulf of Mexico, GoM）各河口捕获的幼年公牛鲨（Carcharhinus leucas）的摄食生态学时空动态与个体发育趋势展开表征与探究。鲨鱼的食物组成以鱼类类群为主，其相对重要性指数（index of relative importance, %IRI）占比超过98%；在鉴定至科级的猎物类群中，有2个科的IRI占比超过50%，分别为鲻科（Mugilidae，鲻鱼：约32%）与石首鱼科（Sciaenidae，石首鱼和叫姑鱼：27%）。鲱科（Clupeidae，鲱鱼：14%）与海鲶科（Ariidae，海鲶：15%）同样对幼年鲨鱼的食物贡献显著，不过当幼年鲨鱼叉长（Fork Length, FL）超过893mm（约1龄）时，其对海鲶科的摄食占比随鲱科摄食占比的下降而升高。δ¹⁵N值随鲨鱼体型增长显著升高，表明随着鲨鱼体型增大，其摄食对象逐渐转向体型更大或营养层级更高的猎物。δ¹³C与δ³⁴S的纬度与时间变化趋势显示，同位素组成的变异与所采样河口的初级生产者群落结构及环境驱动因子存在对应关系。本研究结果凸显了淡水-海洋连续体中的硬骨鱼猎物资源对幼年公牛鲨摄食的重要性，同时验证了天然同位素示踪剂在追踪摄食生态学个体发育趋势方面的应用价值。