Life-history traits of the marbled electric ray, Torpedo marmorata Risso, 1810, from the Greek Seas, north-eastern Mediterranean Sea

This work presents new information on the morphological aspects, reproductive biology and diet of the marbled electric ray Torpedo marmorata Risso 1810, in the Eastern Ionian and the Aegean Seas, from October 2017 to August 2020. The whole dataset consisted of 135 females and 109 males, ranging between 91–464 mm and 99–313 mm in total length (TL), respectively. The weight–length relationship of the species and the length frequency distribution of the sexes were described, corroborating the sexual dimorphism of the species. Thirty-one measurements were recorded to test the allometric growth of several characters for female and male specimens, whereas additional metrics (four) were used to investigate its reproductive cycle, in the north-eastern Mediterranean Sea. Sex ratio analysis was not significantly different from the 1:1 ratio. The size at which 50% of the species attained sexual maturity (L50) was the lowest recorded within the Mediterranean Sea for both sexes (261 mm for females and 241 mm for males). Mature males occurred throughout the year, whilst mature females (capable to reproduce) were present in spring and early autumn. The number of embryos ranged from five to 13 per brood. Stomach content examination revealed a preference of T. marmorata for fishes, with differences in prey item consumption between the Ionian and the Aegean Sea. This is the first attempt to describe the life-history traits of T. marmorata in the Greek Seas that will contribute to the future conservation status of the species.