Diet and trophic structure of fishes in the Barents Sea: Seasonal and spatial variations

A large-scale stomach sampling program was carried out in 2015 where 27.627 stomachs from 70 fish species (including two genera) were collected and analysed. This provided a baseline for further trophic investigations in the Barents Sea (BS). Here, we focus on spatial and seasonal variations in fish diet and feeding intensity, and how the trophic structure of fish communities varies between seasons. Principal component analysis revealed the position of 34 selected fish species with a pattern reflecting the three groups of piscivores, planktivores, and benthivores. Copepods, krill and hyperiid amphipods were the dominant prey for two groups or clusters of planktivorous fishes. Piscivores generally fed on a wide range of fish species, supplemented by benthic prey such as epibenthic mobile crabs and shrimps, and pelagic prey such as euphausiids and hyperiid amphipods. The benthivores had a more diverse and complex diet. Small benthivorous fishes were feeding on polychaetes, small benthic crustaceans (gammarid amphipods, isopods, and mysids), and hyperiids. These fishes, which feed in the interface between the water column and the seafloor, direct their foraging attention either downwards to eat polychaetes, small molluscs, and echinoderms, or upwards to feed on hyperbenthic amphipods, isopods, and pelagic hyperiids. Our results show the clearest signs of seasonality for the planktivore groups which feed on zooplankton and use the seasonal 'pulse' of the new generations (e.g. of Calanus finmarchicus) developing in spring and summer. Piscivores also utilize seasonally available prey related to feeding and spawning migrations, notably of capelin and polar cod. Despite the seasonality, the overall trophic structure with the main groups of planktivores, piscivores, and benthivores persisted over the seasons. Biogeographical affiliation contributes both to spatial divergence between Arctic and boreal species in the BS, and to spatial integration through migrations and wide distributions of Arctic-boreal and 'mainly boreal' species. Habitat association contributes to spatial divergence and reduced competition between species in the same trophic clusters, e.g. between species distributed in shallow versus deeper waters. This work improves our knowledge about seasonal and spatial variation in the trophic interactions of the Barents Sea fish community and forms the basis for further studies of energy flow in the Barents Sea ecosystem.