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Research Papers
Introduction
The bullet tuna Auxis rochei (Risso, 1810) (Osteichthyes: Scombridae) is a pelagic fish distributed in tropical and subtropical areas, including the Mediterranean Sea (Uchida, 1981). The limits of its distribution are not well known, mainly because this species is often confused with its congener, the frigate tuna Auxis thazard (Lacepède, 1800), another cosmopolitan fish (Di Natale et al., 2009). In fact, the systematics of the genus Auxis is still controversial: some authors consider the species synonymous (Collignon, 1961; Nair et al., 1970), while others recognize the existence of two distinct species (Yesaki & Arce, 1991; Collette & Aadland, 1996). Although at present the latter hypothesis is the one considered valid (Catanese et al., 2008), recent genetic and morphometric studies showed that A. rochei is the only species distributed in the Mediterranean Sea and in the adjacent areas of the Atlantic Ocean (Orsi Relini et al., 2008), suggesting that some occurrences of this species from this area could have been misidentified as A. thazard, even in scientific papers (Orsi Relini et al., 2009).
Auxis rochei, which is the most abundant tuna in the Mediterranean Sea, represents an important component of the food web (Mostarda et al., 2007) and is exploited by artisanal fisheries, representing 39% of the total tuna landings in the Mediterranean area (9829 t in 2010; FAO, 2011). The migrations of A. rochei in the Atlantic Ocean have rarely been studied; Grudtsev (1992) suggested that it may undertake a trophic migration along the north-west coast of Africa, and Richards & Simmons (1971) suggested that spawning took place south of the Islands of Cape Verde. In addition, little is known about its life cycle and migrations in the Mediterranean Sea. Tortonese (1963) and Reglero et al. (2012) reported that A. rochei performs local migrations around the spawning areas in the neritic habitat of the mainland and islands, whereas Sabatés & Recasens (2001) proposed a spawning migration from the Atlantic Ocean to the western Mediterranean Sea.
Parasites are useful tags to investigate the biology, ecology, migration and population structure of marine organisms (MacKenzie & Abaunza, 2014), and they have also been used successfully to clarify...