Historical ecology of the Mediterranean population of Great White Shark, Carcharodon carcharias.

The Great White Shark Carcharodon carcharias, as many large sharks, is threatened by human impacts. Presently it is considered as Critically Endangered in the Mediterranean Sea and Endangered in the rest of the World by the IUCN. Its ecological role as top predator is essential in maintaining the coastal and pelagic ecosystem function, therefore strong efforts have been made worldwide towards their conservation, including the implementation of knowledge and empirical data on migratory behaviour and feeding ecology. In this perspective, the present thesis aims to understand the historical ecology of the Mediterranean population of Great White Shark taking advantage from the multi-element analysis of stable isotopes (i.e. carbon, nitrogen, zinc and strontium) of several historical remains archived in civic and academic Italian museums and private collections. Since Great White Shark is a large epipelagic migratory shark, the first point of the research is to provide information about the movements between Mediterranean and adjacent Atlantic Ocean by the estimate of the isotopic composition of carbon (¹³C/¹²C) and nitrogen (¹⁵N/¹⁴N) from the collagen of jaws, teeth, and vertebrae. Additional analyses of the ontogenetic shifts were carried out by a sequential carbon, nitrogen, and zinc analyses of four vertebrae belonging to a single individual archived in the Massimo Sella collection at the University of Bologna; in addition, one fossil tooth from Borgo Tossignano was dated back using 87Sr/86Sr isotope composition. The results indicated that these multidisciplinary analyses need to be improved to assess the correct isotopic footprint and wonder to understand the historical ecology of Great White Shark population in the Mediterranean Sea, but it is a very promising methodology that has already made it possible to understand that white sharks in the Mediterranean Sea are not an isolated population.