Seasonality of skipjack tuna parasites in the Eastern Atlantic provide an insight into its migratory patterns

A sample of 128 skipjack tuna Katsuwonus pelamis from Madeira archipelago was the subject of a parasitological analysis, in order to identify seasonal patterns of parasite infection which can provide information regarding the migratory patterns of skipjack tuna in the Eastern Atlantic. A total of 24 parasite taxa were detected. The nematode Oncophora melanocephala (Nematoda: Camallanidae) was identified as a first record for the genus Katsuwonus and several species were detected for the first time in the Eastern Atlantic, including the didymozoid trematode Pozdnyakovia gibsoni (Trematoda: Didymozoidae), originally described in skipjack tuna from Brazil. Generalized Linear Modelling (GLM) analysis revealed season and host fork length as the main predictors of parasite abundance, uncovering seasonal patterns of infection that indicate that migration to waters around Madeira occurs in at least two separate stages, and suggests a mixing of skipjack tuna sub-populations from both sides of the Atlantic.