Ecology of the Atlantic black skipjack Euthynnus alletteratus (Osteichthyes: Scombridae) in the western Mediterranean Sea inferred by parasitological analysis

Between 2008 and 2011, the head of 150Euthynnus alletteratus(Osteichthyes: Scombridae) caught inshore offthesoutheastern Iberian coast (western Mediterranean Sea) were examined for parasites. Two monogeneans, four didymozoidtrematodes and four copepods were found. Parasite abundance showed a positive relationship with the annual sea surfacetemperature, except forPseudocycnus appendiculatus, but negative with the sea depth (Capsala manteri, Neonematobothriumcf.kawakawaandCaligus bonito). Prevalences and mean abundances differed significantly among sampling areas, exceptforC. manteri, Oesophagocystissp. 2 andCeratocolax euthynni, and sampling years (Melanocystiscf.kawakawa, N.cf.kawa-kawa, P. appendiculatusandUnicolax collateralis). Results indicate that the parasite abundances ofE. alletteratusin thewestern Mediterranean Sea depend mainly on regional environmental variables, which can show interannual variations.The presence of pelagic parasites, i.e. didymozoids andP. appendiculatus, could indicate thatE. alletteratusmigratesbetween inshore and offshore pelagic domains. The different parasite faunas reported inE. alletteratuspopulationsfrom the western Atlantic Ocean and the Mediterranean Sea appear to point out the geographical host isolation. Theseresults suggest thatE. alletteratusinhabiting the western Mediterranean Sea performs inshore-offshore small-scale migra-tions, and not transoceanic migrations between the western Atlantic Ocean and Mediterranean Sea.