Abstract
The Norwegian skate Dipturus nidarosiensis (Storm, 1881) has only recently been recorded in the western Mediterranean Sea along the coast of southern Sardinia, off Algeria and the Alboran Sea. The present study confirmed the presence of the species in the Central Mediterranean Sea by identifying morphometric, morphological features and molecular markers. Biological sampling was conducted from 2010 to 2016 on eight specimens collected through commercial landings, offshore observer programmes and scientific surveys in Adriatic and Ionian waters at depths between 320 and 720 m. The total lengths of the specimens (juveniles and adults) ranged from 268 to 1,422 mm, and their body weights ranged from 44.5 to 12,540.0 g. They showed morphometric features that corresponded to those of Norwegian skates in the Northeast Atlantic and the Western Mediterranean. In previous analyses, molecular data were obtained by mitochondrial COI sequences. The haplotype network showed the occurrence of a common haplotype (Hap_1) shared by the individuals from areas in the North Atlantic, Sardinian, Algerian and Spanish Mediterranean Sea areas but not South Africa. The occurrence of individuals in different stages of life (i.e., juveniles, sub-adults and adults) and sexual development (immature and mature) suggested the presence of a species with a permanent reproductive allocation in the deep waters of the Mediterranean, which was exposed to a low level of fishing exploitation. Indeed, the deep depth distribution of the species could be the reason for the absence of information about this species in onshore or offshore fishery data collection programmes and scientific surveys.
Highlights
Species discrimination is a challenging issue mainly because it is based only on morphological diagnoses
The genetic analysis of the mitochondrial gene c oxidase I gene (COI) made it possible to confirm the morphological identification of the Adriatic–Ionian samples as D. nidarosiensis
In this study, the molecular data revealed that the Mediterranean specimens of D. nidarosiensis shared COI mitochondrial haplotypes with the Atlantic specimens
Summary
Species discrimination is a challenging issue mainly because it is based only on morphological diagnoses. The use of molecular markers, the cytochrome c oxidase I gene (COI), has proven to be very helpful on several occasions in the identification of ray and skate species in the Mediterranean, Atlantic and other waters worldwide (Ball et al, 2016; Bineesh et al, 2017; Cannas et al, 2010; Cariani et al, 2017; Cerutti-Pereyra et al, 2012; Coulson et al, 2011; Frodella et al, 2016; Griffiths et al, 2013; Iglesias, Toulhoat & Sellos, 2010; Landi et al, 2014; Lynghammar et al, 2014; Mabragana et al, 2011; Ordines et al, 2017; RamírezAmaro et al, 2017; Serra-Pereira et al, 2011; Spies et al, 2006; Vargas-Caro et al, 2016; Vella, Vella & Schembri, 2017; Ward et al, 2008; Ward et al, 2005; Martin Dia zDe Astarloa et al, 2008)
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