New insights into life–history traits of Mediterranean Electric rays (Torpediniformes: Torpedinidae) as a contribution to their conservation

Andrea Bellodi;Antonello Mulas;Pierluigi Carbonara;Alessandro Cau;Danila Cuccu;Martina Francesca Marongiua;Veronica Mura;Paola Pesci;Walter Zupa;Cristina Porcu;Maria Cristina Follesa

2021-01-01

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Abstract

Despite being commonly recognized by the general public, knowledge about the biology and life-history of electric rays is still scarce. Globally, according to the International Union for Conservation of Nature, more of the 80% of the species belonging to the Torpedinidae family are, indeed, classified as Data Deficient, so as, in most of the cases, no proper management measures are available for the conservation of these species. For this reason, the main goal of this study is to provide new information on life-history traits of three species inhabiting the Mediterranean Sea. Age and growth were estimated through direct annuli count of 146 vertebral centra sections of Torpedo marmorata. Females’ growth pattern was found to be better described by a S-shaped function (Gompertz L∞ = 622 mm TL; k = 0.15; IP = 2.75 years), while males’ by a logarithmic one (von Bertalanffy L∞ = 485 mm TL; k = 0.14; t0 = -2.28). The oldest female and male were aged 17 (560 mm TL) and 11 (432 mm TL), respectively. Females (L50 = 379 mm TL and A50 = 5.5 years) appeared to mature later than males (L50 = 272 mm TL and A50 = 3.8 years), also attaining bigger sizes. Despite the observation of late-pregnant females being found only in autumn and regressing ones in autumn and winter, the presence of uveniles dur- ing the whole year may indicate a longer reproductive period. The stomach content analysis identified T. marmorata as a top predator (TROP = 4.38) with a very narrow trophic niche (Bi = 0.22), etremely specialized in feeding on bony fishes. In addition, this work provides new and updated information on T. torpedo and the rare Tetronarce nobiliana growth, reproductive features and diet. Therefore, offering new essential data to assess the population conditions of all Torpedinidae species that inhabit the Mediterranean Sea, will lead to effective conservation plans.