Stable-isotope analysis (SIA) provides a valuable tool to address complex questions pertaining to elasmobranch ecology. Liver, a metabolically active, high turnover tissue (~166 days for 95% turnover), has potential to reveal novel insights into recent feeding/movement behaviours of this diverse group. To date, limited work has used this tissue, but ecological application of SIA in liver requires consideration of tissue preparation techniques given the potential for high concentrations of urea and lipid that could bias δ13 C and δ15 N values (i.e. result in artificially lower δ13 C and δ15 N values). Here we investigated the effectiveness of: i) deionized water washing (WW) for urea removal from liver tissue and ii) chloroform-methanol for extraction of lipids from this lipid rich tissue. We then; i) established C:N thresholds for deriving ecologically relevant liver isotopic values given complications of removing all lipid and ii) undertook a preliminary comparison of δ13 C values between tissue pairs (muscle and liver) to test if observed isotopic differences correlated with known movement behaviour. Tests were conducted on four large shark species; the dusky (DUS; Carcharhinus obscurus), sand tiger (RAG; Carcharias taurus), scalloped hammerhead (SCA; Sphyrna lewini) and white shark (GRE; Carcharodon carcharias). There was no significant difference in δ15 N values between lipid-extracted (LE) liver and lipid-extracted/water washed (WW) treatments, however, WW resulted in significant increases in %N, δ13 C and %C. Following lipid extraction (repeated three times), some samples were still biased by lipids. Our species-specific 'C:N thresholds' provide a method to derive ecologically viable isotope data given the complexities of this lipid rich tissue (C:N thresholds of 4.0, 3.6, 4.7 and 3.9 for DUS, RAG, SCA and GRE liverLEWW tissue, respectively). The preliminary comparison of C:N threshold corrected liver and muscle δ13 C values corresponded with movement/habitat behaviours for each shark; minor difference in δ13 C values were observed for known regional movements of DUS and RAG (δ13 CDiffs = 0.24 ± 0.99‰ and 0.57 ± 0.38‰, respectively), while SCA and GRE showed greater differences (1.24 ± 0.63‰ and 1.08 ± 0.71‰, respectively) correlated to large scale movements between temperate/tropical and pelagic/coastal environments. These data provide an approach for the successful application of liver δ13 C and δ15 N values to examine elasmobranch ecology.

中文翻译：

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确定适当的预处理程序和肝组织在鲨鱼体内稳定同位素（δ 13 C 和δ 15 N）研究中的应用

稳定同位素分析 (SIA) 提供了一种有价值的工具来解决与弹鳃生态学有关的复杂问题。肝脏是一种代谢活跃的高周转组织（约 166 天，95% 的周转率）有可能揭示对这个不同群体最近的进食/运动行为的新见解。迄今为止，使用这种组织的工作有限，但考虑到高浓度的尿素和脂质可能会使 δ13 C 和 δ15 N 值产生偏差（即导致人为地降低 δ13 C），因此 SIA 在肝脏中的生态应用需要考虑组织制备技术和 δ15 N 值）。在这里，我们研究了以下效果：i) 去离子水洗涤 (WW) 用于从肝组织中去除尿素和 ii) 氯仿-甲醇用于从富含脂质的组织中提取脂质。然后我们; i) 成立 C：考虑到去除所有脂质的并发症，推导出生态相关肝脏同位素值的 N 阈值和 ii) 对组织对（肌肉和肝脏）之间的 δ13 C 值进行了初步比较，以测试观察到的同位素差异是否与已知的运动行为相关。对四种大型鲨鱼进行了测试；昏暗（DUS；Carcharhinus obscurus）、沙虎（RAG；Carcharias taurus）、扇形锤头鲨（SCA；Sphyrna lewini）和白鲨（GRE；Carcharodon carcharias）。脂质提取 (LE) 肝脏和脂质提取/水洗 (WW) 处理之间的 δ15 N 值没有显着差异，但是，WW 导致 %N、δ13 C 和 %C 显着增加。在脂质提取（重复 3 次）之后，一些样品仍然受到脂质的影响。我们特定物种的“C:N 阈值” 鉴于这种富含脂质的组织的复杂性（DUS、RAG、SCA 和 GRE 肝脏LEWW 组织的 C:N 阈值分别为 4.0、3.6、4.7 和 3.9），提供了一种推导出生态上可行的同位素数据的方法。C:N 阈值校正肝脏和肌肉 δ13 C 值的初步比较与每条鲨鱼的运动/栖息地行为相对应；观察到 DUS 和 RAG 已知区域运动的 δ13 C 值存在微小差异（δ13 CDiffs = 0.24 ± 0.99‰ 和 0.57 ± 0.38‰），而 SCA 和 GRE 显示出更大的差异（1.24 ± 0.63‰ 和 1.08 ± 0.71‰） ，分别）与温带/热带和远洋/沿海环境之间的大规模运动相关。这些数据为成功应用肝脏 δ13 C 和 δ15 N 值来检查弹鳃生态学提供了一种方法。