Many sharks and other marine taxa use natal areas to maximize survival of young, meaning such areas are often attributed conservation value. The use of natal areas is often linked to predator avoidance or food resources. However, energetic constraints that may influence dispersal of young and their use of natal areas are poorly understood. We combined swim-tunnel respirometry, calorimetry, lipid class analysis and a bioenergetics model to investigate how energy demands influence dispersal of young in a globally distributed shark. The school shark (a.k.a. soupfin, tope), Galeorhinus galeus, is Critically Endangered due to overfishing and is one of many sharks that use protected natal areas in Australia. Energy storage in neonate pups was limited by small livers, low overall lipid content and low levels of energy storage lipids (e.g. triacylglycerols) relative to adults, with energy stores sufficient to sustain routine demands for 1.3–4 days (mean ± SD: 2.4 ± 0.8 days). High levels of growth-associated structural lipids (e.g. phospholipids) and high energetic cost of growth suggested large investment in growth during residency in natal areas. Rapid growth (~40% in length) between birth in summer and dispersal in late autumn–winter likely increased survival by reducing predation and improving foraging ability. Delaying dispersal may allow prioritization of growth and may also provide energy savings through improved swimming efficiency and cooler ambient temperatures (daily ration was predicted to fall by around a third in winter). Neonate school sharks are therefore ill-equipped for large-scale dispersal and neonates recorded in the northwest of their Australian distribution are likely born locally, not at known south-eastern pupping areas. This suggests the existence of previously unrecorded school shark pupping areas. Integrated bioenergetic approaches as applied here may help to understand dispersal from natal areas in other taxa, such as teleost fishes, elasmobranchs and invertebrates.

中文翻译：

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成长还是离开？鲨鱼幼崽从产卵区扩散的能量限制

许多鲨鱼和其他海洋类群使用出生区来最大限度地提高年轻人的生存率，这意味着这些区域通常具有保护价值。出生区域的使用通常与避免捕食者或食物资源有关。然而，可能影响年轻人散布和他们使用出生区域的能量限制却知之甚少。我们结合了游泳隧道呼吸测定法、热量测定法、脂质类别分析和生物能量学模型来研究能量需求如何影响全球分布的鲨鱼中幼体的扩散。学校鲨鱼（又名汤鳍，tope），Galeorhinus galeus，由于过度捕捞而极度濒危，是澳大利亚许多使用受保护出生区的鲨鱼之一。新生幼崽的能量储存受限于肝脏小、总脂质含量低和能量储存脂质水平低（例如 三酰基甘油）相对于成人，其能量储存足以维持 1.3-4 天的日常需求（平均值 ± SD：2.4 ± 0.8 天）。高水平的生长相关结构脂质（例如磷脂）和高能量的生长成本表明在出生区居住期间对生长的大量投资。在夏季出生到深秋冬季扩散之间的快速生长（长度约为 40%）可能通过减少捕食和提高觅食能力来增加存活率。延迟分散可能允许优先考虑生长，也可能通过提高游泳效率和降低环境温度来节省能源（预计冬季日粮量将下降约三分之一）。因此，新生的学校鲨鱼没有能力进行大规模传播，并且在澳大利亚分布的西北部记录的新生儿很可能是在当地出生的，而不是在已知的东南部产卵区。这表明存在以前未记录的学校鲨鱼幼崽区。此处应用的综合生物能方法可能有助于了解其他类群的出生区域的扩散，例如硬骨鱼、软骨鱼类和无脊椎动物。