Parasites as tags for stock identification of a highly exploited vulnerable skate Dipturus brevicaudatus (Chondrichthyes: Rajidae) in the south-western Atlantic Ocean, a complementary tool for its conservation

Populations of chondrichthyans are particularly sensitive to elevated fishing mortality due to their low reproductive potential and very low population growth. Dipturus brevicaudatus is a common and endemic skate from waters of Argentina and is frequently caught as by-catch and is therefore extremely vulnerable to commercial fishing. There are signs of overfishing in both the northern and southern Argentine Sea and the species has been classified as 'Vulnerable' by the International Union for Conservation of Nature. A parasitological examination of 96 skates revealed 1,913 individual macroparasites belonging to 18 species and one myxozoan. Three parasite species were long-lived and were suitable biological tags, resulting in statistically significant differences between North Patagonic and both Buenos Aires and South Patagonic regions and therefore can be used to identify stocks of D. brevicaudatus. The inclusion of short-lived parasites in the analyses suggested the existence of three stocks. Parasite assemblages from the northern Argentine Sea (Buenos Aires, Argentine biogeographical province) and from Patagonian waters (North and South Patagonic, Magellanic biogeographical province) varied in terms of parasite infracommunity species richness and the relative abundance of parasite guilds. Using parasites to infer the existence of three stocks of D. brevicaudatus provides the basis to help establishing management and recovery strategies to preserve the diversity of this vulnerable skate in the south-west Atlantic Ocean. Due to the low host specificity of the long-lived parasite tags, there is potential to extend this methodology to other skate species that are commercially exploited in the region, whose population structures remain unknown.