Trophic ecology of pelagic fish species off the Iberian coast: diet overlap, cannibalism and intraguild predation

This work presents, for the first time, a comparative study of the feeding ecology of the most abundant pelagic fish (PF) species (sardines, anchovies, chub mackerel, horse mackerel, bogue, jack mackerel, Mediterranean horse mackerel) in the Western Iberian Upwelling Ecosystem (WIUE). Special attention is given to understanding how the trophic ecology of PF can affect sardine population dynamics, which have been declining in recent years. Diet composition was estimated for juvenile and adult fish collected off the western and southern Iberian coasts during spring by determining the contribution of different prey types and prey size-classes to total dietary carbon. Results show that PF have highly diversified diets, with mesozooplankton and prey ranging from 1000 to 2000 mu m being the major contributors to total dietary carbon. Calanoid copepods were important prey for all PF. Despite these similarities, there were significant differences in diet composition between areas, species, and maturity stages. Small prey such as phytoplankton, crustacean eggs, nauplii and small copepods were particularly important for the diet of sardines and juvenile chub mackerel. Prey >1500 mu m (including decapod larvae, euphausiids and mysids) were mostly important for anchovies, adult chub mackerel, bogue, horse mackerel, jack mackerel and Mediterranean horse mackerel. Chub mackerel juveniles had the highest diet overlap with sardines. Sardine and chub mackerel juveniles, followed by bogue, were the main predators of fish eggs, particularly those of sardines, suggesting further investigation of their role in egg mortality and recruitment strength. This is particularly relevant given the recent northward expansion of chub mackerel into the main spawning grounds of sardines off the WIUE.