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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 δ15N- and δ13C-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. [ABSTRACT FROM AUTHOR]

Shorthorn sculpin (Myoxocephalus scorpius) commonly occur in nearshore areas during open water periods in the Arctic, yet little is known about their feeding strategies or trophic roles. This study used carbon (δ13C) and nitrogen (δ15N) stable isotopes (SIs) and stomach content analysis (SCA) to assess shorthorn sculpin trophic position (TP), carbon sources, dietary specialization and prey selection, and the significance of polar cod (Boreogadus saida) in their diet across body size and multiple years. Sculpin TP increased with body size [range = 4.0 ± 0.1 (< 20 cm) to 4.6 ± 0.2 (> 25 cm)] and was consistent with SCA; smaller individuals fed predominantly on invertebrates while larger fed more on fishes. Shorthorn sculpin had high % reliance on pelagic resources (α) for a benthic fish, from 0.62 ± 0.05 to 0.63 ± 0.06, thus coupling benthic and pelagic sources. Dietary specialization based on SIs in liver and muscle occurred in all size groups, and along with TP and niche width varied between years, generally increasing with fish found in SCA. The presence of polar cod, absent two of the four study years, did not significantly affect any dietary metrics measured in shorthorn sculpin, and cannibalism appears to have had a greater impact on shorthorn sculpin trophic ecology. This study demonstrates that shorthorn sculpin are an important secondary to tertiary consumer in nearshore Arctic marine habitats due to coupling multiple trophic pathways, demonstrating plasticity in diet between years, and exploiting an array of prey across size ranges. [ABSTRACT FROM AUTHOR]

We provide preliminary carbon (δ13C) and nitrogen (δ15N) stable isotope assessment of the Greenland halibut ( Reinhardtius hippoglossoides) diet in Cumberland Sound, with focus on two possible prey sources: pelagic represented by capelin ( Mallotus villosus) and epibenthic represented by shrimp ( Lebbeus polaris). The δ13C for the Greenland halibut stock indicated a pelagic carbon source in Cumberland Sound while stable isotope mixing models, IsoSource and MixSIR, indicated a 99% dietary composition of capelin relative to the shrimp. The δ15N did not vary across Greenland halibut size ranges and placed them at a fourth trophic position relative to a primary herbivore. This study provides the starting point for more elaborate Cumberland Sound research on the local Greenland halibut feeding ecology by confirming pelagic feeding and establishing relative trophic position as well as identifying stable isotopes as a useful tool for the study of diet in cold water fish species. [ABSTRACT FROM AUTHOR]