A molecular approach towards taxonomic identification of elasmobranch species from Maltese fisheries landings

Abstract

The mitochondrial genome, through the application of DNA barcoding, provides a powerful tool for identifying species even when specimens are either incomplete or belong to species that exhibit cryptic diversity. In fisheries management accurate identification of whole or part of the specimens landed is a fundamental requirement for the conservation of species affected directly or indirectly by the fisheries activities. In this study cytochrome c oxidase subunit I (COI) and NADH dehydrogenase subunit 2 (ND2) sequences were used to genetically distinguish 36 elasmobranch species collected from Maltese (Central Mediterranean) commercial fisheries landings. Each species was analysed using these two mtDNA loci where COI (610bp) and ND2 (990bp) efficiently distinguished between the various species studied, leading to the identification of 101 haplotypes, with the intraspecific p-distance ranging between 0 and 0.75% (mean 0.10%, SD ±0.13%). This study enhances the molecular data available on elasmobranchs by providing new ND2 sequences for various species, while providing both COI and ND2 data for poorly studied Mediterranean species including: the large pelagic sharks Alopias vulpinus, A. superciliosus, Carcharhinus altimus, C. plumbeus, Carcharadon carcharias, Isurus oxyrinchus, Prionace glauca and Odontaspis ferox; the smaller demersal sharks Somniosus rostratus, Squatina aculeata, S. oculata and Squalus sp.; and the endemic stingray Dasyatis tortonesei. It also confirmed the landings of species whose identification relies strongly on molecular tools, namely Squalus sp. and D. tortonesei, which are both first confirmed records amongst Maltese fisheries landings. Morphologically, the latter two species, can be easily misidentified with S. blainville and D. pastinaca respectively. Additionally, this study evaluated the genetic differences between different polychromatic forms of Raja clavata, R. radula and Dipturus oxyrinchus. Based on the currently analysed specimens, no significant genetic differences were found between the various forms and thus no further speciation within the species was identified.