Diets of sculpins (Myoxocephalus spp.) and Arctic char (Salvelinus alpinus) during a spring resource pulse in the Canadian Arctic.

The Arctic is one of the fastest-warming marine regions in the world, which is changing the timing of seasonal sea-ice dynamics. The annual summer breakup of sea-ice coincides with resource pulses, which provide critical food sources for consumers to exploit. Marine organisms respond behaviourally to exploit these resources, with some migrating to presumably maximize feeding opportunities, whereas others remain resident, providing an ideal model to assess potential variability in fish movements and feeding. To assess variability in how migratory and resident fishes exploit increases in resource availability associated with ice-off, we collected stomach contents from anadromous Arctic char (Salvelinus alpinus; n = 91) and resident sculpins (Myoxocephalus spp.; n = 190) in Tremblay Sound, Nunavut, Canada, during the ice-free seasons of 2017-2019. Despite eating larger prey, Arctic char experienced lower relative consumption [mean ± standard deviation (SD); 1.92% body mass ± 1.38%] than sculpins (2.88% ± 2.93%). Arctic char also had fewer empty stomachs (n = 1; 1.96%) than sculpins (n = 11; 14.7%). Of identified prey categories, 52.6% (n = 10 categories) were shared by both consumers, but notable exceptions occurred. Non-metric multidimensional scaling (NMDS) ordination revealed dietary distinctions primarily driven by Arctic char's higher consumption of fishes and copepods, whereas sculpins fed heavily on amphipods. Our findings are consistent with sedentary and benthic-oriented resident sculpins intermittently consuming small, benthic prey at high levels, whereas mobile, semipelagic, migratory Arctic char consume pelagic prey at consistent levels that likely do not impede aerobic activity. Ultimately, diets are reflective of consumer physiology but are also influenced by migratory versus resident movement strategies and likely interannual variation in prey abundance, providing insight into strategies used by fishes in the extremely seasonal Arctic, which may become increasingly consequential with climate change.