SGER: Nursery areas, natal origin, and natural elemental signatures: implications for connectivity and conservation of shark and ray populations

育儿区的使用在鳍科动物(鲨鱼和银鱼)中很普遍。由于幼体和成体栖息地的不同物理和化学特征，幼体和成体栖息地的分离创造了将独特的元素成分并入生长个体的钙化结构的可能性。元素的独特比例和组合可以作为自然产生的标记，通常被称为元素特征，提供对出生来源、栖息地使用、扩散、连通性和种群混合程度的洞察。然而，这些工具还没有被应用于软骨鱼类。这项研究的目的是确定结合在一年幼鱼的椎骨中的元素标记是否反映了离散的、特定部位的标记。这项调查可能会为研究这类鱼的生活史和种群动态建立一种强有力的替代方法。棘鳍缺乏钙化结构，称为耳石，通常用于根据独特的元素特征研究多骨鱼类的扩散和出生起源。钙化椎体内的潜在代谢活动引发了人们对这些结构的化学稳定性的质疑。这种细胞基质的再吸收或生理性重塑可能会改变一生中脊椎的化学成分，并限制它们作为有机体过去生活的物理化学环境的记录的有效性。在根据软骨椎内化学成分的差异考虑更广泛的生态问题之前，必须解决这些技术应用的关键假设。补充的野外和圈养实验室调查将用于评估脊椎元素特征的时空变异性，水和脊椎化学成分之间的关系，以及这些特征随时间的稳定性。标本将在2008年8月至11月和2009年8月至11月期间从墨西哥(包括加利福尼亚州海湾)和哥斯达黎加太平洋沿岸苗圃地区的渔业上岸获得。采样位置的分布将能够评估元素和同位素特征在10s、100s和1000s尺度上的空间变异性，跨越不同的环境和地质梯度。研究物种将机会性地以代表不同的生活史策略和生态形态类型(例如底栖、中上层)为目标，但重点将集中在常见上岸的环全球分布的扇形锤头鲨(Sphy Rna Lewini)的收集上。脊椎内元素被区别或选择的程度将通过分配系数来描述，从而能够将脊椎的化学成分与环境浓度进行比较。水和脊椎化学与元素特征的时间稳定性之间的关系将通过圈养的幼鲨或射线的操纵实验来评估。实验处理将包括一个对照和三个恒定盐度-温度水平的重复条件。在大约九个月的时间之后，每个水箱中的盐度-温度处理将被改变，以模拟到一个新的、对比鲜明的环境中的变化。在转移时，一辆坦克将被分配减少的口粮。这将提供一种方法来确定生理压力，如不规律的食物供应或不足，是否会促使脊椎基质中的元素重新工作。在9个月后，实验标本将根据机构动物保护和使用委员会的协议被牺牲。对于脊椎样品，将使用激光烧蚀电感耦合等离子体质谱进行元素和同位素分析；对于水样，将结合电感耦合等离子体光发射光谱和高分辨率电感耦合等离子体质谱进行元素和同位素分析。该项目是对软骨脊椎多元素分析在出生起源和种群连通性研究中的潜在应用的首次探索。如果这项技术成功，这项研究将推动和指导未来的研究，并为改善对这一历史上脆弱的鱼类群体的管理和保护提供关键细节。

The use of nursery areas is widespread among elasmobranchs (sharks and rays). The segregation of juvenile and adult habitat creates the potential for distinctive elemental compositions to be incorporated into the calcified structures of growing individuals as a result of the differing physical and chemical characteristics of these nursery areas. Distinctive ratios and combinations of elements may serve as naturally occurring markers, commonly referred to as elemental signatures, providing insight into natal origins, habitat use, dispersal, connectivity, and the extent of population mixing. However, these tools have not yet been applied to cartilaginous fishes. The objective of this investigation is to determine if elemental signatures incorporated into the vertebrae of young-of-the-year elasmobranchs reflect discrete, site-specific markers. This investigation may establish a powerful, alternative approach for research into the life history and population dynamics of this group of fishes. Elasmobranchs lack the calcified structures, known as otoliths, which are typically used for studies of dispersal and natal origin in bony fishes based on distinctive elemental signatures. The potential for metabolic activity within calcified vertebrae has raised questions about the chemical stability of these structures. Resorption or physiological reworking of this cellular matrix may alter vertebral chemical composition during the course of a lifetime and limit their usefulness as records of past physiochemical environments in which the organism lived. Before broader ecological questions may be considered based on differences in the chemical composition within cartilaginous vertebrae, key assumptions underlying the application of these techniques must be addressed.Complementary field and captive laboratory investigations will be applied to assess spatial and temporal variability of vertebral elemental signatures, relationships between water and vertebral chemical composition, and stability of these signatures through time. Specimens will be obtained from fishery landings from nursery areas along the Pacific coast of Mexico (including the Gulf of California) and Costa Rica during August-November 2008 and 2009. The distribution of the sampling locations will enable an assessment of spatial variability in elemental and isotopic signatures on the scale of 10s, 100s, and 1000s of kms across contrasting environmental and geological gradients. Study species will be opportunistically targeted to represent different life history strategies and ecomorphotypes (e.g. benthic, pelagic), but an emphasis will be focused on the collection of the commonly landed, circumglobally distributed scalloped hammerhead shark (Sphyrna lewini). The extent to which elements are discriminated against or selected for within vertebrae will be described by partition coefficients, thus enabling comparisons of vertebral chemical composition with ambient environmental concentrations.Relationships between water and vertebral chemistry and temporal stability of elemental signatures will be assessed through manipulative experiments with captive juvenile sharks or rays. Experimental treatments will include a control, and replicated conditions of three constant salinity-temperature levels. Following a period of approximately nine months, salinity-temperature treatments will be altered in each tank to simulate change into a new, contrasting environment. At the time of transfer, one tank will be assigned reduced food rations. This will provide a means of determining if physiological stress, such as an irregular or insufficient food supply, drives reworking of elements within the vertebral matrix. After nine additional months have passed, experimental specimens will be sacrificed in accordance with Institutional Animal Care and Use Committee protocol. Elemental and isotopic analyses will be conducted using Laser Ablation Inductively Coupled Plasma Mass Spectrometry for vertebral samples and a combination of Inductively Coupled Plasma Optical Emission Spectroscopy and High Resolution Inductively Coupled Plasma Mass Spectrometry for water samples. This project represents the first inquiry into the potential application of multi-elemental analysis of cartilaginous vertebrae to studies of natal origin and population connectivity. If the technique is successful, this study will propel and direct future research and provide critical details for improved management and conservation of this historically vulnerable group of fishes.