Towards the conservation of vulnerable marine large predators: morphometric, molecular and microchemical variation of historical sawfish rostra from Mediterranean collections

Sawfishes (Chondrichthyes, Pristidae) are considered one of the most endangered families among elasmobranchs. Extensive efforts are required worldwide to gather solid information on historical and recent changes in the composition/range of species. In this study, we have implemented an integrative approach to characterize the species diversity and the abundance of historical rostra of sawfishes from museums and private collections of the Mediterranean area. The identification at the species level of 172 dried rostra was carried out through the integration of both traditional and geometric morphometric techniques with molecular tools, allowing the assessment of a robust methodical approach to discriminate species. In addition, we analysed 35 rostral teeth to clarify the past distribution of sawfish species considering the isotopic composition of oxygen and carbon. The morphometric, molecular, and geographical characterization of samples was accompanied by the preliminary evaluation of growth structures and the inspection of the strontium isotope composition in two teeth to unravel movement patterns of individuals across different salinities of water. Results were integrated with currently available data from public repositories and showed that the historical specimens belonged to four nominal species: Pristis zijsron (81), Anoxypristis cuspidata (39), P. pristis (30), and P. pectinata (22). An identification error of 5.41% emerged in the morphological distinction of rostra between juvenile individuals of P. pectinata and P. zijsron. The new approach of carbon and oxygen isotopes, implemented for the first time in these taxa, permitted the identification of the high-probability habitat preferences of these benthopelagic elasmobranchs in about 50% of the analysed specimens. Using this multidisciplinary approach, we successfully assigned the numerous museum rostra with lacking data to a given species and identified their candidate geographical origin, retrieving novel information and data for understanding the species distribution and ecology of past, sometimes locally/regionally extinct sawfish faunas.