Population genetics of the critically endangered Myliobatis aquila (Linnaeus, 1758) across the Gibraltar Strait

The common eagle ray, Myliobatis aquila (Linnaeus, 1758), is a demersal and semi-pelagic ray with a wide distribution including the eastern Atlantic Ocean and Mediterranean Sea, and the western Indian Ocean. During the last 40 years the populations of this species have declined due to overfishing and habitat loss to the point that it is considered Critically Endangered by the International Union for Conservation of Nature. In this context, it is urgent to increase the biological and ecological knowledge of this species in order to improve its current management and conservation measures. A key trait for management plans is the connectivity among populations. The present study aimed at evaluating the population genetic structure of the eagle ray from six locations across the Mediterranean and the East Atlantic using two mitochondrial markers (COI and ND2). Analyses of molecular variance, based on the concatenated sequences of both markers, showed no significant genetic differentiation among all sampling locations. On the contrary, when measuring pairwise fixation indices, a slight differentiation in individuals from South Africa, Adriatic Sea and Balearic Islands was observed. However, the haplotype network and the Bayesian clustering analyses both indicated the existence of a single population. Future studies, employing more informative markers and combining genetic studies with tagging methods will be needed to understand and further investigate migration dynamics of M. aquila. In this context, the findings of this work offer preliminary information about the high connectivity of this species, whose future conservation and management is strongly recommended.