Broad feeding niches of capelin and sand lance may overlap those of polar cod and other native fish in the eastern Canadian Arctic

As ocean temperatures rise, sub-Arctic capelin ( Mallotus villosus ) and sand lance ( Ammodytes spp.) have become increasingly abundant in regions of the eastern Canadian Arctic. These fish have a similar trophic role to the keystone polar cod ( Boreogadus saida ), potentially competing for food resources when co-occurring. To evaluate this, we calculated feeding niche breadth and overlap based on fatty acids and δ 15 N- and δ 13 C-derived trophic position and carbon source, among sub-Arctic fish and 10 Arctic fish and invertebrates within low, mid, and high latitudes of the Canadian Arctic. Diverse feeding strategies including benthic Myoxocephalus sp., anadromous and pelagic fish, led to limited feeding niche overlap among species (13% average, range 0–96%). Feeding niche overlap between capelin and sand lance from the low Arctic was generally high (36–93%); while fatty acid niches of these fish overlapped 0–21% with polar cod in the mid and high Arctic, and their isotopic niches overlapped up to 96%. Capelin and sand lance showed 3–8 times broader feeding niches than polar cod. Regarding regional variation, polar cod had similar niche breadth between regions and highly overlapping fatty acid niches. Niche variation for Myoxocephalus sp. and Gammarus spp. between low and high Arctic was likely associated with more diverse sources of primary production in the shallower, more brackish low Arctic. Although regional variation in food availability play an important role defining feeding niches, broader niches and isotopic niche overlap with polar cod indicated a potential ecological advantage for capelin and sand lance over polar cod under climate change.