Diet composition and feeding behavior of capelin (Mallotus villosus) in the changing Iceland–East Greenland–Jan Mayen ecosystem

This study investigates how the diet composition and feeding behavior of capelin (Mallotus villosus), a key forage fish in the Iceland-East Greenland-Jan Mayen (IEGJM) ecosystem, has changed subsequent to a pronounced shift of their feeding areas to East Greenland. Capelin diets were analysed in their new feeding area in autumn (September–October) from 2018 to 2021. Feeding occurred with a high proportion of capelin stomachs containing food (77–98%). Euphausiids (mainly Thysanoessa inermis) and copepods (mainly Calanus hyperboreus and C. finmarchicus) dominated their diets, reflecting the local zooplankton community, and indicating a shift from a previously copepod-dominated diet to a combination of euphausiids and copepods in the new feeding areas. The dominant prey groups varied spatially and among years, suggesting that capelin feed flexibly in response to local prey availability. Stable nitrogen isotope analysis indicated that larger capelin fed at higher trophic levels, with δ15N values suggesting consumption of larger prey over longer timescales. Our study offers valuable insights into the diet and feeding ecology of capelin and highlights its dependence on ocean conditions. This information is essential for predicting the impacts of environmental changes on the IEGJM food web.