The use of parasites as biological tags for stock identification of blue jack mackerel, Trachurus picturatus, in the North-eastern Atlantic

The use of parasites as biological tags for discriminating stocks of blue jack mackerel, Trachurus picturatus (Osteichthyes, Carangidae), in the northeast Atlantic Ocean is assessed herein. In this study the following parasites have been selected as possible biological tags: Anisakis spp. (Nematoda: Anisakidae), Rhadinorhynchus sp. (Acanthocephala: Rhadinorhynchidae), Nybelinia sp. (Cestoda: Tentaculariidae) and Bolbosoma sp. (Acanthocephala: Polymorphidae). Anisakis spp. was the most prevalent parasite taxon found in all localities, attaining higher values in fish from Peniche, mainland Portugal. The occurrence of Rhadinorhynchus sp. in fish from all studied areas was rare (prevalence <10%) but significantly different between localities, with higher values in both archipelagos. Nybelinia sp. specimens were only detected in fish from Madeira and cystacanths of the genus Bolbosoma were never detected. The distinctive pattern of infection of these parasite species points to the existence of three stocks of blue jack mackerel in the northeast Atlantic: one in Portuguese mainland waters, one in Madeira archipelago and another in the Canary archipelago. These results support the management strategy which treats the three populations studied as separate stocks.