Trace elements and isotopes analysis on historical samples of white sharks (Carcharodon carcharias) from central Mediterranean Sea

Both trace elements and isotopes analysis were performed on two samples of vertebrae of White Sharks Carcharodon carcharias from Favignana Island (Sicily, central Mediterranean). For the trace elements analysis, the ICP-MS associated by Laser Ablation allowed us to find 36 trace elements. More samples were taken, on the same vertebrae, along a transect that goes from the most central part of the vertebra to the distal one. Among these 36 trace elements we have been detected high concentrations of Pb, Fe, Zn, Sr, Ba and U. Fluctuations of these elements can be caused by different kind of processes such as variations in temperature, nutrition, uptake of urban pollutants and proximity to industrial areas. The stable isotopes (δ15N and δ13C) analysis has been performed through IRMS (Isotope Ratio Mass Spectrometry) and allowed us to understand the trophic levels of individuals. The two white shark vertebrae showed different isotopic values. The first individual (seven growth layers) presented isotopic ranges from 9.6‰ to 10.8‰ (δ15N) and from -16.5‰ to - 13.0‰ (δ13C); this showed a mean ± SD value of 10.3 ± 0.4‰ for δ15N and -14.6 ± 1.3‰ for δ13C. The second individual (five growth layers) presented isotopic ranges from 9.8‰ to 11.1‰ (δ15N) and from -16.9‰ to -15.0‰ (δ13C), displaying a mean ± SD value of 10.8 ± 0.6‰ for δ15N and -15.8 ± 0.8‰ for δ13C. In terms of δ15N values, there were not significant differences (U = 6, p =0.07346) between the two individuals; however, there were significant differences (t = -1.8, p =0.049256) in δ13C values, both at a significance level of 0.05. The absence of differences between the trophic level of the individuals could be related to the trophic level of their preys at the time of age. The differences observed in the case of δ13C are probably correlated to the fact that the first shark was feeding near the coast, while the other feed more offshore.