Sea ice dynamics structure narwhal presence and seasonal movements in a Northwest Greenland fjord system

The Arctic is experiencing unprecedented environmental change, with diminishing sea ice reshaping marine ecosystems. The narwhal (Monodon monoceros) exhibits strong site fidelity during seasonal movements and continued sea-ice decline has the potential to alter important habitats. This study aimed to understand narwhal presence at different sea-ice stages by combining long-term passive acoustic monitoring (PAM) with satellite-derived sea ice data from Inglefield Bredning, Northwest Greenland (June 2022-September 2025). Generalized linear mixed models (GLMMs) revealed a highly significant effect of sea-ice stage on narwhal acoustic activity (p < 0.001). Activity peaked during partial ice cover (β = 1.73 ± 0.17, p < 0.001) but declined sharply under open-water and freeze-up conditions (β = - 0.98 ± 0.19, p < 0.001). These results demonstrate that narwhal presence is closely synchronized with sea-ice timing and extent, emphasizing the marginal ice zone as a key ecological feature that narwhals exploit, likely because it provides both feeding opportunities and refuge from predators. Continued loss of seasonal sea ice is therefore expected to alter narwhal movement patterns, potentially increasing fjord residency and reducing inter-fjord movements. Such behavioural shifts could have cascading ecological effects, altering prey dynamics and reducing genetic exchange among regional narwhal groups.