Consumption of mesopelagic prey in the Strait of Messina, an upwelling area of the central Mediterranean Sea: feeding behaviour of the blue jack mackerel Trachurus picturatus (Bowdich, 1825)

Abstract

This study describes for the first time the feeding behaviour and mesopelagic food consumption of adult Trachurus picturatus in the Strait of Messina (central Mediterranean Sea), where the distinctive hydrodynamic regime and the lunar cycle influence food availability for this predator. Indeed, the Strait of Messina is characterized by the upwelling of colder, saltier and nutrient-rich Levantine Intermediate Water, supporting the congregation and abundance of the mesopelagic community. Despite the commercial importance of T. picturatus in the Mediterranean and Atlantic fisheries, its trophic ecology is almost unknown. Overall, 262 specimens of T. picturatus were collected from small-scale fisheries of the Strait of Messina (September 2016–August 2017) and their stomach content was examined to investigate dietary composition and feeding strategy. Although the absence of a dominant prey item ruled out specialized predatory behaviour in T. picturatus, mesopelagic prey dominated the diet of this species and a significant fraction of food (more than 80% in terms of Index of Relative Importance) was represented by euphausiids and mesopelagic fish. The predator exploitation of mesopelagic prey resources was analysed, considering the ecological implications of the hydrodynamic regime of the study area, which is strongly influenced by upwelling processes linked to the lunar cycle. For this reason, we tested and confirmed the hypothesis that moon phases could influence the food intake of T. picturatus and seasonal variations in the diet as well as size-related dietary shift were also observed.