Modelled atmospheric and ocean conditions across spatial scales and ice periods associated with Arctic fish isotopic resource use

Understanding the mechanisms by which environmental conditions affect Arctic fish populations is of increasing importance given effects of rapid climate change in the Canadian Arctic. We assessed Arctic fish diet and habitat use indicated by stable isotope values (δ 13 C and δ 15 N) in relation to modelled atmospheric and ocean conditions and climate indices in the Canadian Arctic. Coastal, anadromous, and offshore marine fish were sampled from 12 sub-areas across the Beaufort Sea, Amundsen Gulf, and Frobisher Bay from 2011 to 2020. Generalized additive mixed-effects models were used to investigate relationships between mean-standardized isotope values for fish functional groups and modelled atmospheric, ice, and ocean conditions across multiple spatial scales during the ice-covered, ice break-up, and open-water periods, and linkages between environmental conditions in coastal and offshore marine habitats. Environmental variables in offshore areas were not conclusively linked to resource use of coastal fish, however variables across spatial scales (e.g., local surface downward stress, snow thickness and surface layer temperature, regional cyclone system density, and hemispheric climate indices) were the most frequently selected predictors of fish isotopic resource use. Although environmental variables explained only some of the variability in fish stable isotope values, our results indicate that important environmental conditions have similar relationships with fish resource use across feeding ecologies and habitat domains. During the open-water period, winds, storms, and surface mixed layer temperature were important predictors of fish stable isotope values, and could influence availability of fish prey due to migration and advection. During the ice-covered period, the importance of winds, storms, and snow cover are likely to have been associated with fish stable isotopes via bottom-up influences on the timing of phytoplankton production, potentially leading to lagged food-web shifts. Atmospheric variables were important predictors across spatial scales, suggesting fish resource use across feeding ecologies may be influenced more by region-scale, rather than habitat-specific, associations.