Diet of capelin (Mallotus villosus) in the Eastern Canadian Arctic inferred from stomach contents and stable isotopes.

Capelin (Mallotus villosus), a sub-Arctic forage fish, has become abundant in the Canadian Arctic in recent decades, with consistent spawning documented; however, the trophic role of capelin in these systems is unknown. We investigated the diets of small, immature (70–129 mm), medium, mature (130–174 mm), and large, mature (175–219 mm) capelin in Pangnirtung Fjord, Nunavut during and prior to spawning in June–July, 2015–2016 using stomach contents and stable isotopes, respectively. Ontogenetic niche shifts were observed in both cases. Small, immature capelin consumed predominantly small copepods (primarily Clausocalanidae) and had a narrow isotopic niche (SEA_C: 0.11 ‰²). In contrast, medium-sized, mature capelin consumed a mix of Calanus copepods, amphipods, and mysids and had a broad isotopic niche (SEA_C range: 0.23–0.51 ‰²), while large, mature capelin consumed higher proportions of large prey types (primarily Calanus hyperboreus and amphipods) and had a narrower isotopic niche (SEA_C range: 0.09–0.26 ‰²). A higher percentage (by dry biomass) of capelin eggs (73–100%) were consumed by mature capelin in 2016, when ice cover in the fjord delayed the initiation of sampling by ~ 10 days after spawning had begun, relative to 2015 (0–9%). Non-egg prey types primarily consisted of amphipods (77–100% by dry biomass, mostly ice-associated Apherusa glacialis) in 2016 and primarily pelagic Calanus copepods (64–99%) in 2015. As capelin diet was broadly similar to other Arctic forage fishes, such as polar cod (Boreogadus saida), high dietary overlap may occur. Findings provide baseline data to examine future changes in capelin diet as well as their trophic interactions in the Canadian Arctic. [ABSTRACT FROM AUTHOR]