Assessing the link between ontogenetic shifts in gill raker and diet composition of Arctic cod Boreogadus saida in the Canadian Beaufort Sea-Amundsen Gulf

Arctic cod Boreogadus saida represents the most widespread and abundant fish in the Arctic Ocean and is a key trophic link in Arctic marine ecosystems. As the Arctic undergoes further rapid warming, understanding the ecological dynamics of this species is critical for developing effective Arctic marine conservation efforts. In this study, we assessed the relationship between ontogenetic shifts in gill raker density and diet composition of Arctic cod in the Canadian Beaufort Sea-Amundsen Gulf, using diet analyses and dietary tracers. Our results support the hypothesis that ontogenetic changes in gill raker density are associated with age-specific dietary shifts, leading to changes in the species’ habitat preferences, from surface to deeper waters in the Canadian Beaufort Sea-Amundsen Gulf. As Arctic cod mature, their gill raker density decreases, making them less efficient at foraging on small prey found near the surface. Older fish, with sparser gill rakers, likely relocate to deeper areas to forage on larger prey, as reflected in their diet item sizes, proportions, and dietary tracers. These insights improve our understanding of how gill raker density, along with factors such as predation and thermoregulation, likely drive diet and habitat shifts in Arctic cod, contributing to our knowledge of their ecological role in Arctic marine systems.