Feeding habits of the bullet tuna Auxis rochei in the southern Tyrrhenian Sea

Abstract

A total of 235 bullet tunas (Auxis rochei) was caught off the north-eastern coast of Sicily between March 2003 and March 2004 for the purpose of studying their feeding habits. The fish were caught by means of an experimental surface gill-net during fishing surveys carried out on a monthly basis. The stomach contents were analysed and the prey identified, counted and weighed. The importance of the different prey types was assessed utilizing several feeding indices while possible size-related changes of the diet composition were highlighted by means of hierarchical cluster analysis, nMDS and SIMPER analysis. The results of this study showed that the bullet tuna is an epipelagic off-shore predator feeding on whatever abundant resource is available in the environment with a preference for planktonic crustaceans, small cephalopods and fish larvae. Among crustaceans, hyperiidean amphipods were the most important prey, with Anchylomera blossevillei as the dominant species, followed by the euphausiacean Stylocheiron maximum. Among cephalopods, Heteroteuthis dispar was recorded frequently while fish larvae showed high values of all indices. All prey were pelagic organisms. A size-related change in the diet composition was observed, even if it seemed related to the temporal fluctuations of the zooplanktonic assemblage in the environment. The average prey weight per stomach increased significantly in the larger predators which mostly fed on fish larvae belonging to several commercially important demersal and pelagic species.

Relationships between otolith size and fish size in some mesopelagic and bathypelagic species from the Mediterranean Sea (Strait of Messina, Italy)

“…However, to this day, the lack of data in these area has not always permitted an appropriate quantification of their prey biomass and classification to species level in the diet of Mediterranean pelagic predators. In fact, quite a high percentage of unidentified mesopelagic fishes and otoliths in swordfish and tuna stomach contents have been recorded (Sinopoli et al, 2004;Falautano et al, 2007;Mostarda et al, 2007;Romeo et al, 2009). …”

The use of otolith shape and morphometry for identification and size-estimation of five wrasse species in predator-prey studies

“…Despite high occurrence of wrasses in the entire Mediterranean they are not subject to commercial exploitation, although it is not rare to find them as a part of beach seines by-catch or recreational and spearfishing catches (Gordoa et al, 2000). On the other hand, members of this family are important prey of many marine fishes (Pallaoro and Jardas, 1991;Ren˜ones et al, 2002;Mostarda et al, 2007) and top-predator seabirds (Velando and Freire, 1999).…”

Cephalopods in the diet of young-of-the-year bluefin tuna (Thunnus thynnusL. 1758, Pisces: Scombridae) from the southern Tyrrhenian Sea (central Mediterranean Sea)

“…Predation on the European flying squid T. sagittatus was significant also in the Adriatic Sea, as reported by Piccinetti and Piccinetti Manfrin (1970), whereas in the western Mediterranean only a few specimens of cephalopods, belonging mainly to Sepiola rondeletii and I. coindetii, were identified in YOY bluefin tuna stomachs (Sanz Brau 1990). The predation on H. dispar has already been reported in the southern Tyrrhenian Sea also for the other pelagic predators Thunnus alalunga (Consoli et al 2008), Auxis rochei (Mostarda et al 2007) and Euthynnus alletteratus (Falautano et al 2007). This sepiolid is among the most abundant cephalopods in the area (Romeo et al 2011) and a huge biomass of H. dispar was also recorded in other Mediterranean locations (Bello 1991(Bello , 1999), suggesting that it may be an important key species in the Mediterranean pelagic food web (Romeo et al 2011).…”