Decadal shifts in Atlantic cod migrations in Icelandic waters (1951–2025)

Abstract Understanding the long-term stability and plasticity of marine migrations is essential for predicting species’ responses to environmental changes. In this study, we analysed 75 years (1951–2025) of tagging data from two spawning areas to characterize the feeding migrations of Atlantic cod in Icelandic waters, evaluating the influence of decadal-scale temperature shifts and prey availability. While overall cod migrations exhibited considerable stability from 1951 to 2025, two distinct periods of alteration emerged in recent decades. During the 1990s and 2000s, the primary migration routes from the southwest spawning regions diverged from the northwest, shifting instead towards the south and southeast. A more recent shift in the 2020s saw cod from both spawning areas moving extensively north of Iceland and towards the Dohrn Bank. Substantial changes were observed in water temperature over the Icelandic shelf, with a 1.6°C warming of near-bottom waters between 1993 and 2003. Cod responses to this warming are primarily indirect, apparently driven by the spatial redistribution of their principal prey, capelin, and the periodic availability of blue whiting. By comparing recent observations with historical records (1950s–2000s), we show that the shift towards the Dohrn Bank represents a recurrent migration pattern that had been absent for several decades. This study highlights the importance of long-term monitoring for understanding species' responses to hydrographic and biological changes and improving predictions of future outcomes.